Dragons of the Air: An Account of Extinct Flying Reptiles
by H. G. Seeley · English · Gutenberg #35316 · 373,910 chars · public domain (US)
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Title: Dragons of the Air: An Account of Extinct Flying Reptiles
Author: H. G. Seeley
Release date: February 18, 2011 [eBook #35316]
Language: English
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DRAGONS OF THE AIR
[Illustration: FIG. 47. RHAMPHORHYNCHUS PHYLLUNUS
SHOWING THE PRESERVATION OF THE WING MEMBRANES
_From the Lithographic slate of Eichstaedt, Bavaria_
_Frontispiece_]
DRAGONS OF THE AIR
AN ACCOUNT OF
EXTINCT FLYING REPTILES
BY
H. G. SEELEY, F.R.S.
PROFESSOR OF GEOLOGY IN KING'S COLLEGE, LONDON; LECTURER ON GEOLOGY
AND MINERALOGY IN THE ROYAL INDIAN ENGINEERING COLLEGE
WITH EIGHTY ILLUSTRATIONS
"I AM A BROTHER OF DRAGONS"
_Job_ xxx. 29
NEW YORK: D. APPLETON & CO.
LONDON: METHUEN & CO.
1901
PREFACE
I was a student of law at a time when Sir Richard Owen was lecturing on
Extinct Fossil Reptiles. The skill of the great master, who built bones
together as a child builds with a box of bricks, taught me that the laws
which determine the forms of animals were less understood at that time
than the laws which govern the relations of men in their country. The
laws of Nature promised a better return of new knowledge for reasonable
study. A lecture on Flying Reptiles determined me to attempt to fathom
the mysteries which gave new types of life to the Earth and afterwards
took them away.
Thus I became the very humble servant of the Dragons of the Air. Knowing
but little about them I went to Cambridge, and for ten years worked with
the Professor of Geology, the late Rev. Adam Sedgwick, LL.D., F.R.S., in
gathering their bones from the so-called Cambridge Coprolite bed, the
Cambridge Greensand. The bones came in thousands, battered and broken,
but instructive as better materials might not have been. My rooms
became filled with remains of existing birds, lizards, and mammals,
which threw light on the astonishing collection of old bones which I
assisted in bringing together for the University.
In time I had something to say about Flying Animals which was new. The
story was told in the theatre of the Royal Institution, in a series of
lectures. Some of them were repeated in several English towns. There was
still much to learn of foreign forms of flying animals; but at last,
with the aid of the Government grant administered by the Royal Society,
and the chiefs of the great Continental museums, I saw all the specimens
in Europe.
So I have again written out my lectures, with the aid of the latest
discoveries, and the story of animal structure has lost nothing in
interest as a twice-told tale. It still presents in epitome the story of
life on the Earth. He who understands whence the Flying Reptiles came,
how they endured, and disappeared from the Earth, has solved some of the
greatest mysteries of life. I have only contributed something towards
solving the problems.
In telling my story, chiefly of facts in Nature, an attempt is made to
show how a naturalist does his work, in the hope that perhaps a few
readers will find happiness in following the workings of the laws of
life. Such an illumination has proved to many worth seeking, a solid
return for labour, which is not to be marketed on the Exchange, but may
be taken freely without exhausting the treasury of Nature's truths. Such
outlines of knowledge as here are offered to a larger public, may also,
I believe, be acceptable to students of science and scientific men.
The drawings given in illustration of the text have been made for me by
Miss E. B. Seeley.
H. G. S.
KENSINGTON, _May, 1901_
CONTENTS
PAGE
CHAPTER I.
FLYING REPTILES 1
CHAPTER II.
HOW A REPTILE IS KNOWN 4
CHAPTER III.
A REPTILE IS KNOWN BY ITS BONES 11
CHAPTER IV.
ANIMALS WHICH FLY 15
CHAPTER V.
DISCOVERY OF THE PTERODACTYLE 27
CHAPTER VI.
HOW ANIMALS ARE INTERPRETED BY THEIR BONES 37
CHAPTER VII.
INTERPRETATION OF PTERODACTYLES BY THEIR SOFT PARTS 45
CHAPTER VIII.
THE PLAN OF THE SKELETON 58
CHAPTER IX.
THE BACKBONE, OR VERTEBRAL COLUMN 78
CHAPTER X.
THE HIP-GIRDLE AND HIND LIMB 93
CHAPTER XI.
SHOULDER-GIRDLE AND FORE LIMB 107
CHAPTER XII.
EVIDENCES OF THE ANIMAL'S HABITS FROM ITS REMAINS 134
CHAPTER XIII.
ANCIENT ORNITHOSAURS FROM THE LIAS 143
CHAPTER XIV.
ORNITHOSAURS FROM THE MIDDLE SECONDARY ROCKS 153
CHAPTER XV.
ORNITHOSAURS FROM THE UPPER SECONDARY ROCKS 172
CHAPTER XVI.
CLASSIFICATION OF THE ORNITHOSAURIA 187
CHAPTER XVII.
FAMILY RELATIONS OF PTERODACTYLES TO ANIMALS WHICH LIVED WITH THEM 196
CHAPTER XVIII.
HOW PTERODACTYLES MAY HAVE ORIGINATED 213
APPENDIX 231
INDEX 233
LIST OF ILLUSTRATIONS
FIG. PAGE
47. Wings of Rhamphorhynchus _Frontispiece_
1. Lung of the lung-fish Ceratodus 5
2. Attachment of the lower jaw in a Mammal and in a Pterodactyle 12
3. Chaldaean Dragon 15
4. Winged human figure from the Temple of Ephesus 16
5. Flying fish Exocoetus 18
6. Flying Frog 19
7. Flying Lizard (Draco) 20
8. Birds in flight 22
9. Flying Squirrel (Pteromys) 24
10. Bats, flying and walking 25
11. Skeleton of _Pterodactylus longirostris_ 28
12. The skeleton restored 29
13. The animal form restored 30
14. Fore limbs in four types of mammals 38
15. Pneumatic foramen in Pterodactyle bone 46
16. Lungs of the bird Apteryx 48
17. Air cells in the body of an Ostrich 49
18. Lung of a Chameleon 51
19. Brain in Pterodactyle, Mammal, Bird, and Reptiles 53
20. Skull of Kingfisher and Rhamphorhynchus 63
21. Skull of Heron and Rhamphorhynchus 65
22. Palate of Macrocercus and ? Campylognathus 71
23. Lower jaw of Echidna and Ornithostoma 76
24. First two neck vertebrae of Ornithocheirus 81
25. Middle neck vertebrae of Ornithocheirus 83
26. Back vertebra of Ornithocheirus and Crocodile 86
27. Sacrum, with hip bones, of Rhamphorhynchus 88
28. Extremity of tail of _Rhamphorhynchus phyllurus_ 91
29. Hip-girdle bones in Apteryx and Rhamphorhynchus 95
30. Pelvis with prepubic bone in Pterodactylus 96
31. Pelvis with prepubic bones in Rhamphorhynchus 97
32. Pelvis of an Alligator seen from below 98
33. Femora: Echidna, Ornithocheirus, Ursus 100
34. Tibia and fibula: Dimorphodon and Vulture 102
35. Metatarsus and digits in three Pterodactyles 104
36. Sternum in Cormorant and Rhamphorhynchus 108
37. Sternum in Ornithocheirus 109
38. Shoulder-girdle bones in a bird and three Pterodactyles 113
39. The Notarium from the back of Ornithocheirus 115
40. The shoulder-girdle of Ornithocheirus 115
41. Humerus of Pigeon and Ornithocheirus 119
42. Fore-arm of Golden Eagle and Dimorphodon 120
43. Wrist bones of Ornithocheirus 124
44. Clawed digits of the hand in two Pterodactyles 125
45. Claw from the hand of Ornithocheirus 129
46. The hand in Archaeopteryx and the Ostrich 130
48. Slab of Lias with bones of Dimorphodon _To face page_ 143
49. Dimorphodon (restored form) at rest 144
50. Dimorphodon (restored form of the animal) _To face page_ 145
51. Dimorphodon skeleton, walking as a quadruped " " 146
52. Dimorphodon skeleton as a biped " " 147
53. Lower jaw of Dorygnathus 149
54. Dimorphodon (wing membranes spread for flight) _To face page_ 150
55. Pelvis of Dimorphodon 151
56. Rhamphorhynchus skeleton (restored) 161
57. Scaphognathus (restoration of 1875) 163
58. Six restorations of Ornithosaurs 164
59. Ptenodracon skeleton (restored) 167
60. _Cycnorhamphus suevicus_ slab with bones _To face page_ 168
61. _Cycnorhamphus suevicus_ (form of the animal) _To face page_ 169
62. _Cycnorhamphus suevicus_ skeleton (restored) 170
63. _Cycnorhamphus Fraasi_ (restored skeleton form
of the animal) _To face page_ 170
64. _Cycnorhamphus Fraasi_ (restoration of the form
of the body) _To face page_ 171
65. Neck vertebra of Doratorhynchus from the Purbeck 173
66. Neck bone of Ornithodesmus from the Wealden 173
67. Sternum of Ornithodesmus, seen from the front 175
68. Sternum of Ornithodesmus, side view, showing the keel 175
69. Diagram of known parts of skull of Ornithocheirus 177
70. Neck bone of Ornithocheirus 179
71. Jaws of Ornithocheirus from the Chalk 180
72. Palate of the English Toothless Pterodactyle 181
73. Two views of the skull of Ornithostoma (Pteranodon) 182
74. Skeleton of Ornithostoma 183
75. Comparison of six skulls of Ornithosaurs 192
76. Pelvis of Ornithostoma 195
77. Skull of Anchisaurus and Dimorphodon 199
78. Skull of Ornithosuchus and Dimorphodon 201
79. The pelvis in Ornithosaur and Dinosaur 204
80. The prepubic bones in Dimorphodon and Iguanodon 206
These figures are greatly reduced in size, and when two or more
bones are shown in the same figure all are brought to the same size
to facilitate the comparison.
DRAGONS OF THE AIR
CHAPTER I
FLYING REPTILES
The history of life on the earth during the epochs of geological time
unfolds no more wonderful discovery among types of animals which have
become extinct than the family of fossils known as flying reptiles. Its
coming into existence, its structure, and passing away from the living
world are among the great mysteries of Nature.
The animals are astonishing in their plan of construction. In aspect
they are unlike birds and beasts which, in this age, hover over land and
sea. They gather into themselves in the body of a single individual,
structures which, at the present day, are among the most distinctive
characters of certain mammals, birds, and reptiles.
The name "flying reptile" expresses this anomaly. Its invention is due
to the genius of the great French naturalist Cuvier, who was the first
to realise that this extinct animal, entombed in slabs of stone, is one
of the wonders of the world.
The word "reptile" has impressed the imagination with unpleasant sound,
even when the habits of the animals it indicates are unknown. It is
familiarly associated with life which is reputed venomous, and is
creeping and cold. Its common type, the serpent, in many parts of the
world takes a yearly toll of victims from man and beast, and has become
the representative of silent, active strength, dreaded craft, and
danger.
Science uses the word "reptile" in a more exact way, to define the
assemblage of cold-blooded animals which in familiar description are
separately named serpents, lizards, turtles, hatteria, and crocodiles.
Turtles and the rest of them survive from great geological antiquity.
They present from age to age diversity of aspect and habit, and in
unexpected differences of outward proportion of the body show how the
laws of life have preserved each animal type. For the vital organs which
constitute each animal a reptile, and the distinctive bony structures
with which they are associated, remain unaffected, or but little
modified, by the animal's external change in appearance.
The creeping reptile is commonly imagined as the antithesis of the bird.
For the bird overcomes the forces that hold even man to the earth, and
enjoys exalted aerial conditions of life. Therefore the marvel is shared
equally by learned and unlearned, that the power of flight should have
been an endowment of animals sprung from the breed of serpents, or
crocodiles, enabling them to move through the air as though they too
were of a heaven-born race. The wonder would not be lessened if the
animal were a degraded representative of a nobler type, or if it should
be demonstrated that even beasts have advanced in the battle of life.
The winged reptile, when compared with a bird, is not less astounding
than the poetic conceptions in Milton's _Paradise Lost_ of degradation
which overtakes life that once was amongst the highest. And on the other
hand, from the point of view of the teaching of Darwin in the theories
of modern science, we are led to ask whether a flying reptile may not be
evidence of the physical exaltation which raises animals in the scale of
organisation. The dominance upon the earth of flying reptiles during the
great middle period of geological history will long engage the interest
of those who can realise the complexity of its structure, or care to
unravel the meaning of the procession of animal forms in successive
geological ages which preceded the coming of man.
The outer vesture of an animal counts for little in estimating the value
of ties which bind orders of animals together, which are included in the
larger classes of life. The kindred relationship which makes the snake
of the same class as the tortoise is determined by the soft vital
organs--brain, heart, lungs--which are the essentials of an animal's
existence and control its way of life. The wonder which science weaves
into the meaning of the word "reptile," "bird," or "mammal," is partly
in exhibiting minor changes of character in those organs and other soft
parts, but far more in showing that while they endure unchanged, the
hard parts of the skeleton are modified in many ways. For the bones of
the reptile orders stretch their affinities in one direction towards the
skeletons of salamanders and fishes; and extend them also at the same
time in other directions, towards birds and mammals. This mystery we may
hope to partly unravel.
CHAPTER II
HOW A REPTILE IS KNOWN
DEFINITION OF REPTILES BY THEIR VITAL ORGANS
The relations of reptiles to other animals may be stated so as to make
evident the characters and affinities which bind them together. Early in
the nineteenth century naturalists included with the Reptilia the tribe
of salamanders and frogs which are named Amphibia. The two groups have
been separated from each other because the young of Amphibia pass
through a tadpole stage of development. They then breathe by gills, like
fishes, taking oxygen from the air which is suspended in water, before
lungs are acquired which afterwards enable the animals to take oxygen
directly from the air. The amphibian sometimes sheds the gills, and
leaves the water to live on land. Sometimes gills and lungs are retained
through life in the same individual. This amphibian condition of lung
and gill being present at the same time is paralleled by a few fishes
which still exist, like the Australian _Ceratodus_, the lung-fish, an
ancient type of fish which belongs to early days in geological time.
This metamorphosis has been held to separate the amphibian type from
the reptile because no existing reptile develops gills or undergoes a
metamorphosis. Yet the character may not be more important as a ground
for classification than the community of gills and lungs in the fish and
amphibian is ground for putting them together in one natural group. For
although no gills are found in reptiles, birds, or mammals, the embryo
of each in an early stage of development appears to possess gill-arches,
and gill-clefts between them, through which gills might have been
developed, even in the higher vertebrates, if the conditions of life had
been favourable to such modification of structure. In their bones
Reptiles and Amphibia have much in common. Nearly all true reptiles lay
eggs, which are defined like those of birds by comparatively large size,
and are contained in shells. This condition is not usual in amphibians
or fishes. When hatched the young reptile is completely formed, the
image of its parent, and has no need to grow a covering to its skin like
some birds, or shed its tail like some tadpoles. The reptile is like the
bird in freedom from important changes of form after the egg is hatched;
and the only structure shed by both is the little horn upon the nose,
with which the embryo breaks the shell and emerges a reptile or a bird,
growing to maturity with small subsequent variations in the proportions
of the body.
[Illustration: FIG. 1 LUNG OF THE FISH CERATODUS
Partly laid open to show its chambered structure (After Guenther)]
THE REPTILE SKIN
Between one class of animals and another the differences in the
condition of the skin are more or less distinctive. In a few amphibians
there are some bones in the skin on the under side of the body, though
the skin is usually naked, and in frogs is said to transmit air to the
blood, so as to exercise a respiratory function of a minor kind. This
naked condition, so unlike the armoured skin of the true Reptilia,
appears to have been paralleled by a number of extinct groups of fossils
of the Secondary rocks, such as Ichthyosaurs and Plesiosaurs, which were
aquatic, and probably also by some Dinosauria, which were terrestrial.
Living reptiles are usually defended with some kind of protection to the
skin. Among snakes and lizards the skin has commonly a covering of
overlapping scales, usually of horny or bony texture. The tortoise and
turtle tribe shut up the animal in a true box of bone, which is cased
with an armour of horny plates. Crocodiles have a thick skin embedding a
less continuous coat of mail. Thus the skin of a reptile does not at
first suggest anything which might become an organ of flight; and its
dermal appendages, or scales, may seem further removed from the feathers
which ensure flying powers to the bird than from the naked skin of a
frog.
THE REPTILE BRAIN
Although the mode of development of the young and the covering of the
skin are conspicuous among important characters by which animals are
classified, the brain is an organ of some importance, although of
greater weight in the higher Vertebrata than in its lower groups.
Reptiles have links in the mode of arrangement of the parts of their
brains with fishes and amphibians. The regions of that organ are
commonly arranged in pairs of nervous masses, known as (1) the olfactory
lobes, (2) the cerebrum, behind which is the minute pineal body,
followed by (3) the pair of optic lobes, and hindermost of all (4) the
single mass termed the cerebellum. These parts of the brain are extended
in longitudinal order, one behind the other in all three groups. The
olfactory lobes of the brain in Fishes may be as large as the cerebrum;
but among Reptiles and Amphibians they are relatively smaller, and they
assume more of the condition found in mammals like the Hare or Mole,
being altogether subordinate in size. And the cerebral masses begin to
be wider and higher than the other parts of the brain, though they do
not extend forward above the olfactory lobes, as is often seen in
Mammals. In Crocodiles the cerebral hemispheres have a tendency to a
broad circular form. Among Chelonian reptiles that region of the brain
is more remarkable for height. Lizards and Ophidians both have this part
of the brain somewhat pear-shaped, pointed in front, and elongated. The
amphibian brain only differs from the lizard type in degree; and
differences between lizards' and amphibian brains are less noticeable
than between the other orders of reptiles. The reptilian brain is easily
distinguished from that of all other animals by the position and
proportions of its regions (see Fig. 19, p. 53).
Birds have the parts of the brain formed and arranged in a way that is
equally distinctive. The cerebral lobes are relatively large and convex,
and deserve the descriptive name "hemispheres." They are always smooth,
as among the lower Mammals, and extend backward so as to abut against
the hind brain, termed the cerebellum. This junction is brought about in
a peculiar way. The cerebral hemispheres in a bird do not extend
backward to override the optic lobes, and hide them, as occurs among
adult mammals, but they extend back between the optic lobes, so as to
force them apart and push them aside, downward and backward, till they
extend laterally beyond the junction of the cerebrum with the
cerebellum. The brain of a Bird is never reptilian; but in the young
Mammal the brain has a very reptilian aspect, because both have their
parts primarily arranged in a line. Therefore the brain appears to
determine the boundary between bird and reptile exactly.
REPTILIAN BREATHING ORGANS
The breathing organs of Birds and Reptiles which are associated with
these different types of brain are not quite the same. The Frog has a
cellular lung which, in the details of the minute sacs which branch and
cluster at the terminations of the tubes, is not unlike the condition in
a Mammal. In a mammal respiration is aided by the bellows-like action of
the muscles connected with the ribs, which encase the cavity where the
lungs are placed, and this structure is absent in the Frog and its
allies. The Frog, on the other hand, has to swallow air in much the same
way as man swallows water. The air is similarly grasped by the muscles,
and conveyed by them downward to the lungs. Therefore a Frog keeps its
mouth shut, and the animal dies from want of air if its mouth is open
for a few minutes.
Crocodiles commonly lie in the sun with their mouths widely open. The
lungs in both Crocodiles and Turtles are moderately dense, traversed by
great bronchial tubes, but do not differ essentially in plan from those
of a Frog, though the great branches of the bronchial tubes are
stronger, and the air chambers into which the lung is divided are
somewhat smaller. The New Zealand Hatteria has the lungs of this
cellular type, though rather resembling the amphibian than the
Crocodile. The lungs during life in all these animals attain
considerable size, the maximum dimensions being found in the terrestrial
tortoises, which owe much of their elevated bulk to the dimensions of
the air cells which form the lungs.
The lungs of Serpents and Lizards are formed on a different plan. In
both those groups of reptiles the dense cellular tissue is limited to
the part of the lung which is nearest to the throat. This network of
blood vessels and air cells extends about the principal bronchial tube
much as in other animals, but as it extends backward the blood vessels
become few until the _tubular_ lung appears in its hinder part, as it
extends down the body, almost as simple in structure as the air bladder
of a fish. Among Serpents only one of these tubular lungs is commonly
present, and the structure has a less efficient appearance as a
breathing organ than the single lung of the fish _Ceratodus_ (Fig. 1).
The Chameleons are a group of lizards which differ in many ways from
most of their nearest kindred, and the lungs, while conforming in
general plan to the lizard type in being dense at the throat, and a
tubular bladder in the body, give off on both sides a number of short
lateral branches like the fingers of a glove (Fig. 18, p. 51).
Thus the breathing organs of reptiles present two or three distinct
types which have caused Serpents and Lizards to be associated in one
group by most naturalists who have studied their anatomy; while
Crocodiles and Chelonians represent a type of lung which is quite
different, and in those groups has much in common. These characters of
the breathing organs contribute to separate the cold-blooded armoured
reptiles from the warm-blooded birds clothed with feathers, as well as
from the warm-blooded mammals which suckle their young; for both these
higher groups have denser and more elastic spongy lung tissue.
It will be seen hereafter that many birds in the most active development
of their breathing organs substantially revert to the condition of the
Serpent or Chameleon in a somewhat modified way. Because, instead of
having one great bronchial tube expanded to form a vast reservoir of air
which can be discharged from the lung in which the reptile has
accumulated it, the bird has the lateral branches of the bronchial tubes
prolonged so as to pierce the walls of the lung, when its covering
membrane expands to form many air cells, which fill much of the cavity
of the bird's body (see Fig. 16). Thus the bird appears to combine the
characters of such a lung as that of a Crocodile, with a condition which
has some analogy with the lung of a Chameleon. It is this link of
structure of the breathing organs between reptiles and birds that
constitutes one of the chief interests of flying reptiles, for they
prove to have possessed air cells prolonged from the lungs, which
extended into the bones.
CHAPTER III
A REPTILE IS KNOWN BY ITS BONES
Such are a few illustrations of ways in which reptiles resemble other
animals, and differ from them, in the organs by means of which the
classification of animals is made. But such an idea is incomplete
without noticing that the bony framework of the body associated with
such vital organs also shows in its chief parts that reptiles are easily
recognised by their bones. I will therefore briefly state how reptiles
are defined in some regions of the skeleton, for in tracing the history
of reptile life the bones are the principal remains of animals preserved
in the rocks; and the soft organs which have perished can only be
inferred to have been present from the persistence of durable
characteristic parts of the skeleton, which are associated with those
soft organs in animals which exist at the present day, and are unknown
in other animals in which the skeleton is different.
THE HANG OF THE LOWER JAW
The manner in which the lower jaw is connected with the skull yields one
of the most easily recognised differences between the great groups of
vertebrate animals.
_In Mammals._--In every mammal--such as the Dog or Sheep--the lower jaw,
which is formed of one bone on each side, joins directly on to the head
of the animal, and moves upon a bone of the skull which is named the
temporal bone. This character is sufficient to prove, by the law of
association of soft and hard parts of the body, that such an animal had
warm blood and suckled its young.
[Illustration: FIG. 2 _PTERODACTYLUS KOCHI_ SKULL OF BEAR
Comparison to show the articulation with the lower jaw in a mammal
and _Pterodactylus Kochi_. The quadrate bone is lettered Q in this
Pterodactyle, and comes between the skull and the lower jaw like the
quadrate bone in a bird and in lizards.]
_In Birds._--In birds a great difference is found in this region of the
head. The temporal bone, which it will be more convenient to name the
squamosal bone, from its squamous or scale-like form, is still a part of
the brain case, and assists in covering the brain itself, exactly as
among mammals. But the lower jaw is now made up of five or six bones.
And between the hindermost and the squamosal there is an intervening bar
of bone, unknown among mammalia, which moves upon the skull by a joint,
just as the lower jaw moves upon it. This movable bone unites with parts
of the palate and the face, and is known as the quadrate bone. Its
presence proves that the animal possessing it laid eggs, and if the
face bones join its outer border just above the lower jaw, it proves
that the animal possessed hot blood.
_In Reptiles._--All reptiles are also regarded as possessing the
quadrate bone. But the squamosal bone with which it always unites is in
less close union with the brain case, and never covers the brain itself.
Serpents show an extreme divergence in this condition from birds, for
the squamosal bone appears to be a loose external plate of bone which
rests upon the compact brain case and gives attachment to the quadrate
bone which is as free as in a bird. Among Lizards the quadrate bone is
usually almost as free. In the other division of existing Reptilia,
including Crocodiles, the New Zealand lizard-like reptile Hatteria,
called Tuatera, and Turtles, the squamosal and quadrate bones are firmly
united with the bones of the brain case, face, and palate, so that the
quadrate bone has no movement; and the same condition appears in
amphibians, such as Toads and Frogs. With these conditions of the
quadrate bone are associated cold blood, terrestrial life, and young
developed from eggs.
_In Fishes._--Bony fishes, and all others in which separate bones build
up the skull, differ from Reptiles and Birds much as those animals
differ from Mammals. The union of the lower jaw with the skull becomes
complicated by the presence of additional bones. The quadrate bone still
forms a pulley articulation upon which the lower jaw works, but between
it and the squamosal bone is the characteristic bone of the fish known
as the hyomandibular, commonly connected with opercular bones and
metapterygoid which intervene, and help to unite the quadrate with the
brain case. In the Cartilaginous fishes there is only one bone
connecting the jaws with the skull on each side. This appears to prove
that just as the structure of the arch of bones suspending the jaw may
be complicated by the mysterious process called segmentation, which
separates a bone into portions, so simplification and variation may
result because the primitive divisions of the material cease to be made
which exists before bones are formed.
The principal regions of the skull and skeleton all vary in the chief
groups of animals with backbones; so that the Reptile may be recognised
among fossils, even in extinct groups of animals and occasionally
restored from a fragment, to the aspect which characterised it while it
lived.
CHAPTER IV
ANIMALS WHICH FLY
The nature of a reptile is now sufficiently intelligible for something
to be said concerning flight, and structures by means of which some
animals lift themselves in the air. It is not without interest to
remember that, from the earliest periods in human records,
representations have been made of animals which were furnished with
wings, yet walked upon four feet, and in their typical aspect have the
head shaped like that of a bird. They are commonly named Dragons.
FLYING DRAGONS
[Illustration: FIG. 3 From _The Battle between Bel and the Dragon_]
The effigy of the dragon survives to the present day in the figure over
which St. George triumphs, on the reverse of the British sovereign. In
the luxuriant imaginations of ancient Eastern peoples, dating back to
prehistoric ages, perhaps 5000 B.C., the dragons present an astonishing
constancy of form. In after-times they underwent a curious evolution, as
the conception of Babylon and Egypt is traced through Assyria to Greece.
The Wings, which had been associated at first with the fore limb of the
typical dragon, become characteristic of the Lion, and of the poet's
winged Horse, and finally of the Human figure itself, carved on the
great columns of the Greek temples of Ephesus. These flying animals are
historically descendants of the same common stock with the dragons of
China and Japan, which still preserve the aspect of reptiles. Their
interest is chiefly in evidence of a latent spirit of evolution in days
too remote for its meaning to be now understood, which has carried the
winged forms higher and ever higher in grade of organisation, till their
wings ceased to be associated with feelings of terror. The Hebrew
cherubim are regarded by H. E. Ryle, Bishop of Exeter, as probably
Dragons, and the figure of the conventional angel is the human form of
the Dragon.
[Illustration: FIG. 4. FIGURE FROM THE TEMPLE OF EPHESUS]
ORGANS OF FLIGHT
Turning from this reference to the realm of mythology to existing
nature, the power of flight is popularly associated with all the chief
types of vertebrate animals--fishes, frogs, lizards, birds, and mammals.
Many of the animals ill deserve the name of flyers, and most are
exceptions to different conditions of existence which control their
kindred, but it is convenient to examine for a little the nature of the
structures by which this movement in the air, which is not always
flight, is made possible. Certain fishes, like the lung-fish Ceratodus,
of Queensland, and the mud-fish Lepidosiren, are capable of leaving the
water and living on land, and for a time breathe air. But neither these
fishes nor Periophthalmus, which runs with rapid movement of its fins
and carries the body more or less out of water, or the climbing perch,
Anabas, carried out of water over the country by Indian jugglers, ever
put on the slightest approach to wings.
FLYING FISHES
[Illustration: FIG. 5. THE FLYING FISH EXOCOETUS
With the fins extended moving through the air]
The flight of fishes is a kind of parachute support not unlike that by
which a folded paper is made to travel in the air. It is chiefly seen in
the numerous species of a genus Exocoetus, allied to the gar-pike
(Belone), which is common in tropical seas, and usually from a foot to
eighteen inches long. They emerge from the water, and for a time support
themselves in the air by means of the greatly developed breast fins,
which sometimes extend backward to the tail fin. Although these fins
appear to correspond to the fore limbs of other animals, they may not be
moved at the will of the fish like the wing of a bird. When the flying
fishes are seen in shoals in the vicinity of ships, those fins remain
extended, so that the fish is said sometimes to travel 200 yards at a
speed of fifteen miles an hour, rising twenty feet or more above the
surface of the sea, travelling in a straight line, though sometimes
influenced by the wind. Here the organ, which is at once a fin and a
wing, consists of a number of thin long rods, or rays, which are
connected by membrane, and vary in length to form an outline not unlike
the wing of a bird which tapers to a point. The interest of these
animals is chiefly in the fact that flight is separated from the
condition of having lungs with which it is associated in birds, for
although the flying fish has an air bladder, there is no duct to connect
it with the throat.
FLYING FROGS
[Illustration: FIG. 6. THE FLYING FROG (RHACOPHORUS)
The membranes of the foot and hand extend between the metatarsal and
metacarpal bones, as well as the bones of the digits.]
Among amphibians the organs of flight are also of a parachute kind, but
of a different nature. They are seen in certain frogs which frequent
trees, and are limited to membranes which extend between the diverging
digits of the hand and foot, forming webs as fully developed as in the
foot of a swimming bird. As these frogs leap, the membranes are expanded
and help to support the weight of the body, so that the animal descends
more easily as it moves from branch to branch. There is no evidence that
the bones of the digits ever became elongated like the fin rays of the
flying fish or the wing bones of a Bat; but the web suggests the basis
of such a wing, and the possibilities under which wings may first
originate, by elongation of the bones of a webbed hand like that of a
Flying Frog.
FLYING LIZARDS
[Illustration: FIG. 7. THE FLYING DRAGON, DRACO
Forming a parachute by means of the extended ribs]
The Reptilia in their several orders are remarkable for absence of any
modification of the arms which might suggest a capacity for acquiring
wings, as being latent in their organisation. Crocodiles, Tortoises, and
Serpents are alike of the earth, and not of the air. But among Lizards
there are small groups of animals in which a limited capacity for
movement through the air is developed. It is best known in the family of
small lizards named Dragons, represented typically by the species _Draco
volans_ found in the Oriental region of the East Indies and Malay
Archipelago.
The organ of flight is produced in an unexpected way, by means of the
ribs instead of the limbs. The ribs extend outward as far as the arms
can stretch, and the first five or six are prolonged beyond the body so
as to spread a fold of skin on each side between the arm and the leg.
The membrane admits of some movement with the ribs. This arrangement
forms a parachute, which enables the animal to move rapidly among
branches of trees, extending the structure at will, so that it is used
with rapidity too quick to be followed by the eye, as it leaps through
considerable distances.
A less singular aid to movement in the air is found in some of the
lizards termed Geckos. The so-called Flying Gecko (_Platydactylus
homalocephalus_) has a fringe unconnected with ribs, which extends
laterally on the sides of the body and tail, as well as at the back and
front of the fore and hind limbs, and between the digits, where the web
is sometimes almost as well developed as among Tree Frogs. This is
essentially a lateral horizontal frill, extending round the body. Its
chief interest is in the circumstance that it includes a membrane which
extends between the wrist bones and the shoulder on the front of the
arm. That is the only part of the fringe which represents the wing
membrane of a bird. The fossil flying reptiles have not only that
membrane, but the lateral membranes at the sides of the body and behind
the arms.
Other lizards have the skin developed in the direction of the
circumference of the body. In the Australian Chlamydosaurus it forms an
immense frill round the neck like a mediaeval collar. But though such an
adornment might break a fall, it could not be regarded as an organ of
flight.
FLYING BIRDS
[Illustration: FIG. 8. POSITION OF BIRDS IN FLIGHT]
The wings of birds, when they are developed so as to minister to flight,
are all made upon one plan; but as examples of the variation which the
organs contributing to make the fore limb manifest, I may instance the
short swimming limb of the Penguin, the practically useless rudiment of
a wing found in the Ostrich or Kiwi, and the fully developed wing of the
Pigeon. The wings of birds obtain an extensive surface to support the
animal by muscular movements of three modifications of structure. First,
the bones of the fore limb are so shaped that they cannot, in existing
birds, be applied to the ground for support and be used like the limbs
of quadrupeds, and are therefore folded up at the sides of the body,
and carried in an unused or useless state so long as the animal hops on
the ground or walks, balancing its weight on the hind legs. Secondly,
there are two small folds of skin, less conspicuous than those on the
arms of Geckos; one is between the wrist bones and the shoulder, and the
smaller hinder membrane is between the upper arm and the body. These
membranous expansions are insignificant, and would in themselves be
inadequate to support the body or materially assist its movements.
Thirdly, the bird develops appendages to the skin which are familiarly
known as feathers, and the large feathers which make the wing are
attached to the skin covering the lower arm bone named the ulna, and the
other bones which represent the wrist and hand. The area and form of the
bird's wing are due to individual appendages to the skin, which are
unknown in any other group of animals. Between the extended wing of the
Albatross, measuring eleven feet in spread, and the condition in the
Kiwi of New Zealand, in which the wing is vanishing, there is every
possible variation in size and form. As a rule, the larger the animal
the smaller is the wing area. The problem of the origin of the bird's
wing is not to be explained by study of existing animals; for the rowing
organ of the Penguin, which in itself would never suggest flight,
becomes an organ of flight in other birds by the growth upon it of
suitable feathers. Anyone who has seen the birds named Divers feeding
under water, swimming rapidly with their wings, might never suspect that
they were also organs of aerial flight. The Ostrich is even more
interesting, for it has not developed flight, and still retains at the
extremities of two of the digits the slender claws of a limb which was
originally no wing at all, but the support of a four-footed animal (Fig.
46, p. 130).
FLYING MAMMALS
Flight is also developed among mammals. The Insectivora include several
interesting examples of animals which are capable of a certain motion
through the air. In the tropical forests of the Malay Archipelago are
animals known as Flying Squirrels, Flying Opossums, Flying Lemurs,
Flying Foxes, in which the skin extends outward laterally from the sides
of the body so as to connect the fore limbs with the hind limbs, and is
also prolonged backward from the hind limbs to the tail. The four digits
are never elongated; the bones of the fore limb are neither longer nor
larger than those of the hind limb, and the foot terminates in five
little claws as in other four-footed animals. This condition is adapted
for the arboreal life which those animals live, leaping from branch to
branch, feeding on fruits and leaves, and in some cases upon insects.
These mammals may be compared with the Flying Geckos among reptiles in
their parachute-like support by extension of the skin, which gives them
one of the conditions of support which contribute to constitute flight.
[Illustration: FIG. 9. FLYING SQUIRREL (PTEROMYS)]
_Bats._--One entire order of mammals--the Bats--not only possess true
wings, but are capable of flight which is sustained, and in some cases
powerful. The wings are clothed with short hair like the rest of the
body, and thus the instrument of flight is unlike that of a bird. The
flight of a Bat differs from that of all other animals in being
dependent upon a modification of the bones of the fore limb, which,
without interfering with the animal's movements as a quadruped, secures
an extension of the wing which is not inferior in area to that which the
bird obtains by elongation of the bones of the arm and fore-arm and its
feathers. The distinctive peculiarity of the Bat's wing is in the
circumstance that four of the digits of the hand have their bones
prolonged to a length which is often equal to the combined length of the
arm and fore-arm. The bones of the digits diverge like the ribs of an
umbrella, and between them is the wing membrane, which extends from the
sides of the body outward, unites the fore limb with the hind limb, and
is prolonged down the tail as in the Flying Foxes. Bats have a small
membrane in front of the bones of the arm and fore-arm stretching
between the shoulder and the wrist, which corresponds with the wing
membrane of a bird; but the remainder of the membranes in Bats' wings
are absent in birds, because their function is performed by feathers
which give the wing its area. The elongated digits of the Bat's wing are
folded together and carried at the sides of the body as though they were
a few quill pens attached to its wrist, where the one digit, which is
applied to the ground in walking, terminates in a claw.
[Illustration: FIG. 10 NEW ZEALAND BAT FLYING. BARBASTELLE WALKING]
The organs which support animals in the air are thus seen to be more or
less dissimilar in each of the great groups of animals. They fall into
three chief types: first, the parachute; secondly, the wing due to the
feathers appended to the skin; and thirdly, the wing formed of membrane,
supported by enormous elongation of the small bones of the back of the
hand and fingers. The two types of true wings are limited to birds and
bats; and no living reptile approximates to developing such an organ of
flight as a wing. Judged, therefore, by the method of comparing the
anatomical structures of one animal with another, which is termed
"comparative anatomy," the existence of flying reptiles might be
pronounced impossible. But in the light which the revelations of geology
afford, our convictions become tempered with modesty; and we learn that
with Nature nothing is impossible in development of animal structure.
CHAPTER V
DISCOVERY OF THE PTERODACTYLE
Late in the eighteenth century, in 1784, a small fossil animal with
wings began to be known through the writings of Collini, as found in the
white lithographic limestone of Solenhofen in Bavaria, and was regarded
by him as a former inhabitant of the sea. The foremost naturalist of the
time, the citizen Cuvier--for it was in the days of the French
Republic--in 1801, in lucid language, interpreted the animal as a genus
of Saurians. That word, so familiar at the present day, was used in the
first half of the century to include Lizards and Crocodiles; and
described animals akin to reptiles which were manifestly related neither
to Serpents nor Turtles. But the term saurian is no longer in favour,
and has faded from science, and is interesting only in ancient history
of progress. The lizards soon became classed in close alliance with
snakes. And the crocodiles, with the Hatteria, were united with
chelonians. Most modern naturalists who use the term saurian still make
it an equivalent of lizard, or an animal of the lizard kind.
CUVIER
[Illustration: FIG. 11. _PTERODACTYLUS LONGIROSTRIS_ (Cuvier)
The remains are preserved with the neck arched over the back, and the
jaws opened upward]
Cuvier defined this fossil from Solenhofen as distinguished by the
extreme elongation of the fourth digit of the hand, and from that
character invented for the animal the name Pterodactyle. He tells us
that its flight was not due to prolongation of the ribs, as among the
living lizards named Dragons; or to a wing formed without the digits
being distinguishable from each other, as among Birds; nor with only one
digit free from the wing, as among Bats; but by having the wing
supported mainly by a single greatly elongated digit, while all the
others are short and terminate in claws. Cuvier described the amazing
animal in detail, part by part; and such has been the influence of his
clear words and fame as a great anatomist that nearly every writer in
after-years, in French and in English, repeated Cuvier's conclusion,
maintained to the end, that the animal is a saurian.
[Illustration: FIG. 12. THE SKELETON OF _PTERODACTYLUS LONGIROSTRIS_
Reconstructed from the scattered bones in Fig. 14, showing the limbs
on the left side]
Long before fashion determined, as an article of educated belief, that
fossil animals exist chiefly to bridge over the gaps between those which
still survive, the scientific men of Germany were inclined to see in the
Pterodactyle such an intermediate type of life. At first Soemmerring and
Wagler would have placed the Pterodactyle between mammals and birds.
GOLDFUSS
[Illustration: FIG. 13. THE _PTERODACTYLUS LONGIROSTRIS_ RESTORED
FROM THE REMAINS IN FIG. 11
Showing positions of the wing membranes with the animal at rest]
But the accomplished naturalist Goldfuss, who described another fine
skeleton of a Pterodactyle in 1831, saw in this flying animal an
indication of the course taken by Nature in changing the reptilian
organisation to that of birds and mammals. It is the first flash of
light on a dark problem, and its brilliance of inference has never been
equalled. Its effects were seen when Prince Charles Bonaparte, the
eminent ornithologist, in Italy, suggested for the group the name
Ornithosauria; when the profound anatomist de Blainville, in France,
placed the short-tailed animal in a class between Reptiles and Birds
named Pterodactylia; and Andreas Wagner, of Munich, who had more
Pterodactyles to judge from than his predecessors, saw in the fossil
animal a saurian in transition to a bird.
VON MEYER
But the German interpretation is not uniform, and Hermann von Meyer, the
banker-naturalist of Frankfurt a./M., who made himself conversant with
all that his predecessors knew, and enlarged knowledge of the
Pterodactyles on the most critical facts of structure, continued to
regard them as true reptiles, but flying reptiles. Such is the influence
of von Meyer that all parts of the world have shown a disposition to
reflect his opinions, especially as they practically coincide with the
earlier teaching of Cuvier. Owen and Huxley in England, Cope and Marsh
in America, Gaudry in France, and Zittel in Germany have all placed the
Pterodactyles as flying reptiles. Their judgment is emphatic. But there
is weight of competent opinion to endorse the evolutionary teaching of
Goldfuss that they rise above reptiles. To form an independent opinion
the modern student must examine the animals, weigh their characters bone
by bone, familiarise himself, if possible, with some of the rocks in
which they are found; to comprehend the conditions under which the
fossils are preserved, which have added not a little to the interest in
Pterodactyles, and to the difficulty of interpretation.
GEOLOGICAL HISTORY OF PTERODACTYLES IN GERMANY
We may briefly recapitulate the geological history. Those remains of
Ornithosaurs which have been mentioned, with a multitude of others which
are the glory of the museums of Munich, Stuttgart, Tuebingen,
Heidelberg, Bonn, Haarlem, and London, have all been found in working
the lithographic stone of Bavaria. The whitish yellow limestone forms
low, flat-topped hills, now isolated from each other by natural
denudation, which has removed the intervening rock. The stone is found
at some distance north of the Danube, in a line due north of Augsburg,
in the country about Pappenheim, and especially at the villages of
Solenhofen, Eichstaedt, Kelheim, and Nusplingen. These beds belong to the
rocks which are named White Jura limestone in Germany, which is of about
the same geological age as the Kimeridge clay in England. Much of it
divides into very thin layers, and in these planes of separation the
fossils are found. They include the _Ammonites lithographicus_ and a
multitude of marine shells, king crabs and other Crustacea, sea-urchins,
and other fossils, showing that the deposit was formed in the sea. The
preservation of jelly-fish, which so soon disappear when left dry on the
beach, shows that the ancient calcareous mud had unusual power of
preserving fossils. Into this sea, with its fishes great and small, came
land plants from off the land, dragonflies and other insects, tortoises
and lizards, Pterodactyles with their flying organs, and birds still
clothed with feathers. Sometimes the wing membranes of the flying
reptiles are found fully stretched by the wing finger, as in examples to
be seen at Munich and in the Yale Museum in Newhaven, in America. At
Haarlem there is an example in which the wing membrane appears to be
folded much as in the wing of a Bat, when the animal hangs suspended,
with the flying membrane bent into a few wide undulations.
The Solenhofen Slate belongs to about the middle period of the history
of flying reptiles, for they range through the Secondary epochs of
geological time. Remains are recorded in Germany from the Keuper beds at
the top of the Trias, which is the bottom division of the Secondary
strata; and I believe I have seen fragments of their bones from the
somewhat older Muschelkalk of Germany.
THEIR HISTORY IN ENGLAND
In England the remains are found for the first time in the Lower Lias of
Lyme Regis, in Dorset, and the Upper Lias of Whitby, in Yorkshire. In
Wuertemberg they occur on the same horizons. They reappear in England, in
every subsequent age, when the conditions of the strata and their
fossils give evidence of near proximity to land. In the Stonesfield
Slate of Stonesfield, in Oxfordshire, the bones are found isolated, but
indicate animals of some size, though not so large as the rare bones of
reputed true birds which appear to have left their remains in the same
deposit.
At least two Pterodactyles are found in the Oxford clay, known from more
or less fragmentary remains or isolated bones; just as they occur in the
Kimeridge Clay, Purbeck Limestone, Wealden sandstones, and especially in
newer Secondary rocks, named Gault, Upper Greensand, and Chalk, in the
south-east of England.
Owing to exceptional facilities for collecting, in consequence of the
Cambridge Greensand being excavated for the valuable mineral phosphate
of lime it contains, more than a thousand bones are preserved, more or
less broken and battered, in the Woodwardian Museum of the University
of Cambridge alone. To give some idea of their abundance, it may be
stated that they were mostly gathered during two or three years, as a
matter of business, by an intelligent foreman of washers of the nodules
of phosphate of lime, which, in commerce, are named coprolites. He soon
learned to distinguish Pterodactyle bones from other fossils by their
texture, and learned the anatomical names of bones from specimens in the
University Museum. This workman, Mr. Pond, employed by Mr. William
Farren, brought together not only the best of the remains at Cambridge,
but most of those in the museums at York and in London, and the
thousands of less perfect specimens in public and private collections
which passed through the present writer's hands in endeavours to secure
for the University useful illustrations of the animal's structure. These
fragments, among which there are few entire bones, are valuable, for
they have afforded opportunities of examining the articular ends of
bones in every aspect, which is not possible when similar organic
remains are embedded in rock in their natural connexions.
In England Flying Reptiles disappear with the Chalk. In that period they
were widely distributed, being found in Bohemia, in Brazil, and Kansas
in the United States, as well as in Kent and other parts of England.
They attained their largest dimensions in this period of geological
time. One imperfect fragment of a bone from the Laramie rocks of Canada
was described, I believe, by Cope, though not identified by him as
Ornithosaurian, and is probably newer than other remains.
ASPECT OF PTERODACTYLES
If this series of animals could all be brought together they would vary
greatly in aspect and stature, as well as in structure. Some have the
head enormously long, in others it is large and deep, characters which
are shared by extinct reptiles which do not fly, and to which some birds
may approximate; while in a few the head is small and compact, no more
conspicuous, relatively, than the head of a Sparrow. The neck may be
slender like that of a Heron, or strong like that of an Eagle; the back
is always short, and the tail may be inconspicuous, or as long as the
back and neck together. These flying reptiles frequently have the
proportions of the limbs similar to those of a Bat, with fore legs
strong and hind legs relatively small; while in some the limbs are as
long, proportionately, and graceful as those of a Deer. With these
differences in proportions of the body are associated great differences
in the relative length of the wing and spread of the wing membranes.
DIMENSIONS OF THE ANIMALS
The dimensions of the animals have probably varied in all periods of
geological time. The smallest, in the Lithographic Slate, are smaller
than Sparrows, while associated with them are others in which the
drumstick bone of the leg is eight inches long. In the Cambridge
Greensand and Chalk imperfect specimens occur, showing that the upper
arm bones are larger than those of an Ox. The shaft is one and a half
inches in diameter and the ends three inches wide. Such remains may
indicate Pterodactyles not inferior in size to the extinct Moas of New
Zealand, but with immensely larger heads, animals far larger than birds
of flight.
The late Sir Richard Owen, on first seeing these fragmentary remains,
said "the flying reptile with outstretched pinions must have appeared
like the soaring Roc of Arabian romance, but with the features of
leathern wings with crooked claws superinduced, and gaping mouth with
threatening teeth." Eventually we shall obtain more exact ideas of their
aspect, when the structures of the several regions of the body have been
examined. The great dimensions of the stretch of wing, often computed at
twenty feet in the larger examples, might lead to expectations of great
weight of body, if it were not known that an albatross, with wings
spreading eleven feet, only weighs about seventeen pounds.
CHAPTER VI
HOW ANIMALS ARE INTERPRETED BY THEIR BONES
There is only one safe path which the naturalist may follow who would
tell the story of the meaning and nature of an extinct type of animal
life, and that is to compare it as fully as possible in its several
bones, and as a whole, with other animals, especially with those which
survive. It is easy to fix the place in nature of living animals and
determine their mutual relations to each other, because all the
organs--vital as well as locomotive--are available for comparison. On
such evidence they are grouped together into the large divisions of
Beasts, Birds, and Reptiles; as well as placed in smaller divisions
termed Orders, which are based upon less important modifications of
fundamental structures. All these characteristic organs have usually
disappeared in the fossil. Hence a new method of study of the hard parts
of the skeleton, which alone are preserved, is used in the endeavour to
discover how the Flying Reptile or other extinct animal is to be
classified, and how it acquired its characters or came into existence.
VARIATIONS OF BONES AMONG MAMMALIA
[Illustration: FIG. 14. THE FORE LIMB IN FOUR TYPES OF MAMMALS
Comparison of the fore limb in mammals, showing variation of form
of the bones with function]
Resemblances and differences in the bones are easily over-estimated in
importance as evidence of pedigree relationship. The Mammalia show, by
means of such skeletons as are exhibited in any Natural History Museum,
how small is the importance to be attached to even the existence of any
group of bones in determining its grade of organisation. The whole Whale
tribe suckle their young and conform to the distinctive characters in
brain and lungs which mark them as being mammals. But if there is one
part of the skeleton more than another which distinguishes the Mammalia,
it is the girdle of bones at the hips which supports the hind limbs. It
is characterised by the bone named the ilium being uniformly directed
forward. Yet in the Whale tribe the hip-girdle and the hind limb which
it usually supports are so faintly indicated as to be practically lost;
while the fore limb becomes a paddle without distinction of digits, and
is therefore devoid of hoofs or claws, which are usual terminations of
the extremities in mammals. Yet this swimming paddle, with its
ill-defined bones--sometimes astonishing in number, as well as in
fewness of the finger bones--is represented by the burrowing fore limb
of the Mole, which lives underground; by the elongated hoofed legs of
the Giraffe, which lives on plains; and the extended arm and finger
bones of the Bat, which are equally mammals with the Whale. From such
comparison it is seen that no proportion, or form, or length, or use of
the bones of the limbs, or even the presence of limbs, is necessarily
characteristic of a mammal. No limitation can be placed upon the
possible diversity of form or development of bones in unknown animals,
when they are considered in the light of such experience of varied
structural conditions in living members of a single class.
What is true for the limbs and the bony arches which support them is
true for the backbone also, for the ribs, and to some extent for the
skull. The neck in the Whale is shortened almost beyond recognition. In
the Giraffe the same seven vertebrae are elongated into a marvellous
neck; so that in the technical definition of a mammal both are said to
have seven neck vertebrae. Yet exceptions show a capacity for variation.
One of the Sloths reduces the number to six, while another has nine
vertebrae in the neck; proving that there is no necessary difference
between a mammal and a reptile when judged by a character which is
typically so distinctive of mammals as the number of the neck bones.
The skull varies too, though to a less extent. The Great Ant-eater of
South America is a mammal absolutely without teeth. The Porpoises have a
simple unvarying row of conical teeth with single roots extending along
the jaw. And the dental armature of the jaws, and relative dimensions of
the skull bones, exhibit such diversity, in evidence of what may be
parted with or acquired, that recognition of the many reptilian
structures and bones in the skull of Ornithorhynchus, the Australian
Duckbill, demonstrates that the difficulties in recognising an animal by
its bones are real, unless we can discover the Animal Type to which the
bones belong; and that there is very little in osteology which may not
be lost without affecting an animal's grade of organisation.
VARIATION IN SKIN COVERING OF MAMMALS
Even the covering of the body varies in the same class, or even order of
animals, so that the familiar growth on the skin is never its only
possible covering. The Indian ant-eater, named Manis, which looks like a
gigantic fir-cone, the Armadillo, which sheathes the body in rings of
bone, bearing only a scanty development of hair, are examples of
mammalian hair, as singular as the quills of a Porcupine, the horn of a
Rhinoceros, or the growth of hair of varying length and stoutness on
different parts of the body in various animals, or the imperfect
development of hair in the marine Cetacea. Among living animals it is
enough for practical purposes to say that a mammal is clothed with hair,
but in a fossil state the hair must usually be lost beyond recognition
from its fineness and shortness of growth.
VARIATION IN SKIN COVERING OF BIRDS
No Class of living animals is more homogeneous than Birds; and
well-preserved remains prove that, at least as far back in time as the
Upper Oolites, birds were clothed with feathers of essentially the same
mode of growth and appearance as the feathers of living birds. There
may, therefore, be no ground for assuming that the covering was ever
different, though some regions of the skin are free from feathers. Yet
the variations from fine under-down to the scale-like feathers on the
wings of a Penguin, or the great feathers in the wings of birds of
flight, or the double quill of the Ostrich group, are calculated to
yield dissimilar impressions in a fossil state, even if the fine down
would be preserved in any stratum.
VARIATION IN THE BONES OF BIRDS
Osteologically there is less variety in the skeleton of birds than in
other great groups of animals. The existing representatives do not
exhaust its capability for modification. The few specimens of birds
hitherto found in the Secondary strata have rudely removed many
differences in the bones which separated living birds from reptiles; so
that if only the older fossil birds were known, and the Tertiary and
living birds had not existed, a bird might have been defined as an
animal having its jaw armed with teeth, instead of devoid of teeth; with
vertebrae cupped at both ends, instead of with a saddle-shaped
articulation which in front is concave from side from side, and convex
from above downwards; in which the bones of the hand are separate, so
that three digits terminating in claws can be applied to the ground,
instead of the metacarpal bones being united in a solid mass with
clawless digits; and in which the tail is elongated like the tail of a
lizard. Yet the limits to variation are not to be formulated till Nature
has exhausted all her resources in efforts to preserve organic types by
adapting them to changed circumstances. Birds may be regarded
theoretically as equally capable with mammals of parting with almost
every distinctive structure in the skeleton by which it is best known.
Even the living frigate bird blends the early joints of the backbone
into a compact mass like a sacrum. The Penguin has a cup-and-ball
articulation in the early dorsal vertebrae, with the ball in front. And
the genus Cypselus has the upper arm bone almost as broad as long,
unlike the bird type. Such examples prove that we are apt to accept the
predominant structures in an animal type as though they were universal,
and forget that inferences based, like those of early investigators, on
limited materials may be re-examined with advantage.
VARIATION IN THE BONES OF REPTILES
The true Reptilia, notwithstanding some strong resemblances to Birds in
technical characters of the skeleton, display among their surviving
representatives an astonishing diversity in the bony framework of the
body, exceeding that of the mammalia. This unlooked-for capacity for
varying the plan of construction of the skeleton is in harmony with the
diversity of structure in groups of extinct animals to which the name
reptiles has also been given. The interval in form is so vast between
Serpent and Tortoise, and so considerable in structure of the skeleton
between these and the several groups of Lizards, Crocodiles, and
Hatteria, that any other diversity could not be more surprising. And the
inference is reasonable that just as mammals live in the air, in the
sea, on the earth, and burrow under the earth, similar modes of
existence might be expected for birds and reptiles, though no bird is
yet known to have put on the aspect of a fish, and no reptiles have been
discovered which roamed in herds like antelopes, or lived in the air
like birds or bats, unless these fossil flying animals prove on
examination to justify the name by which they are known.
Comparative study of structure in this way demolishes the prejudice,
born of experience of the life which now remains on earth, that the
ideas of Reptile and of Flight are incongruous, and not to be combined
in one animal. The comparative study of the parts of animals does not
leave the student in a chaos of possibilities, but teaches us that
organic structures, which mark the grades of life, have only a limited
scope of change; while Nature flings away every part of the skeleton
which is not vital, or changes its form with altering circumstances of
existence, enforced by revolutions of the Earth's surface in geological
time, in her efforts to save organisms from extinction and pass the
grade of life onward to a later age.
The bones are only of value to the naturalist as symbols, inherited or
acquired, and vary in value as evidence of the nature and association of
those vital organs which differentiate the great groups of the
vertebrata.
These distinctive structures, which separate Mammals, Birds, and
Reptiles, are sometimes demonstrated by the impress of their existence
left on the bones; or sometimes they may be inferred from the characters
of the skeleton as a whole.
CHAPTER VII
INTERPRETATION OF PTERODACTYLES BY THEIR SOFT PARTS
THE ORGANS WHICH FIX AN ANIMAL'S PLACE IN NATURE
We shall endeavour to ascertain what marks of its grade of organisation
the Pterodactyle has to show. The organs which are capable of modifying
the bones are probably limited to the kidneys, the brain, and the organs
of respiration. It may be sufficient to examine the latter two.
PNEUMATIC FORAMINA IN PTERODACTYLES
[Illustration: FIG. 15. HEAD OF THE HUMERUS OF THE PTERODACTYLE
ORNITHOCHEIRUS
Showing position of the pneumatic foramen on the ulnar side of the
bone as in a bird]
Hermann von Meyer, the historian of the Ornithosaurs of the Lithographic
Slate, as early as 1837 described some Pterodactyle bones from the Lias
of Franconia, which showed that air was admitted into the interior of
the bones by apertures near their extremities, which, from this
circumstance, are known as pneumatic foramina. He drew the inference,
naturally enough, that such a structure is absolute proof that the
Pterodactyle was a flying animal. It was not quite the right form in
which the conclusion should have been stated, because the Ostrich and
other birds which do not fly have the principal bones pneumatic.
Afterwards, in 1859, the larger bones which Professor Sedgwick, of
Cambridge, transmitted to Sir Richard Owen established this condition as
characteristic of the Flying Reptiles of the Cambridge Greensand. It was
thus found as a distinctive structure of the bones both at the beginning
and the close of the geological history of these animals. Von Meyer
remarks that the supposition readily follows that in the respiratory
process there was some similarity between Pterodactyles and Birds. This
cautious statement may perhaps be due to the circumstance that in many
animals air cavities are developed in the skull without being connected
with organs of respiration. It is well known that the bulk of the
Elephant's head is due to the brain cavity being protected with an
envelope formed of large air cells. Small air cells are seen in the
skulls of oxen, pigs, and many other mammals, as well as in the human
forehead. The head of a bird like the Owl owes something of its imposing
appearance to the way in which its mass is enlarged by the dense
covering of air cells in the bones above the brain, like that seen in
some Cretaceous Pterodactyles. Nor are the skulls of Crocodiles or
Tortoises exceptions to the general rule that an animal's head bones may
be pneumatic without implying a pneumatic prolongation of air from the
lungs. The mere presence of air cells without specification of the
region of the skeleton in which they occur is not remarkable. The holes
by which air enters the bones are usually much larger in Pterodactyles
than in Birds, but the entrance to the air cell prolonged into the bones
is the same in form and position in both groups. So far as can be judged
by this character, there is no difference between them. The importance
of the comparison can only be appreciated by examining the bones side by
side. In the upper arm bone of a bird, on what is known as the ulnar
border, near to the shoulder joint, and on the side nearest to it, is
the entrance to the air cell in the humerus. In the Pterodactyle the
corresponding foramen has the same position, form, and size, and is not
one large hole, but a reticulation of small perforations, one beyond
another, exactly such as are seen in the entrance to the air cell in the
bone of a bird, in which the pneumatic character is found. For it is not
every bird of flight which has this pneumatic condition of the bones;
and Dr. Crisp stated that quite a number of birds--the Swallow, Martin,
Snipe, Canary, Wood-wren and Willow-wren, Whinchat, Glossy-starling,
Spotted-fly-catcher, and Black-headed Bunting--have no air in their
bones. And it is well known that in many birds, especially water birds,
it is only the upper bones of the limbs which are pneumatic, while the
smaller bones retain the marrow.
LUNGS AND AIR CELLS
[Illustration: FIG. 16. LUNGS OF THE BIRD APTERYX PARTLY OPENED ON
THE RIGHT-HAND SIDE
The circles are openings of the bronchial tubes on the surface of the
lung. The notches on the inner edges of the lungs are impressions of
the ribs (After R. Owen)]
[Illustration: FIG. 17. THE BODY OF AN OSTRICH LAID OPEN TO SHOW THE
AIR CELLS WHICH EXTEND THROUGH ITS LENGTH (After Georges Roche)]
It may be well to remember that the lungs of a bird are differently
conditioned from those of any other animal. Instead of hanging freely
suspended in the cone-shaped chamber of the thorax formed by the ribs
and sternum, they are firmly fixed on each side, so that the ribs deeply
indent them and hold them in place. The lungs have the usual internal
structure, being made up of branching cells. The chief peculiarity
consists in the way in which the air passes not only into them, but
through them. The air tube of the throat of a bird, unlike that of a
man, has the organ of voice, not at the upper end in the form of a
larynx, but at the lower end, forming what is termed a syrinx. There is
no evidence of this in a fossil state, although in a few birds the rings
of the trachaea become ossified, and are preserved. But below the syrinx
the trachaea divides into two bronchi, tubes which carry the ringed
character into the lungs for some distance, and these give off branches
termed bronchial tubes, the finer subdivisions from which, in their
clustered minute branching sacs, make up the substance of the lung.
There is nothing exceptional in that. But towards the outer or middle
part of the ventral or under surface of the lungs, four or five rounded
openings are seen on each side. Each of these openings resembles the
entrance of the air cell into a bone, since it displays several smaller
openings which lead to it. Each opening from the lung leads to an air
cell. Those cells may be regarded as the blowing out of the membrane
which covers the lungs into a film which holds air like a mass of soap
bubbles, until the whole cavity of the body of a bird from neck to tail
is occupied by sacculated air cells, commonly ten in number, five on
each side, though two frequently blend at the base of the neck in the
region of the #V#-shaped bone named the clavicle or furculum, popularly
known as the merry-thought. Most people have seen some at least of
these semi-transparent bladder-like air cells beneath the skin in the
abdominal region of a fowl. The cells have names from their positions,
and on each side one is abdominal, two are thoracic, one clavicular, and
one cervical, which last is at the base of the neck. The clavicular and
abdominal air cells are perhaps the most interesting. The air cell
termed clavicular sends a process outward towards the arm, along with
the blood vessels which supply the arm. Thus this air cell, entering the
region of the axilla or arm-pit, enters the upper arm bone usually on
its under side, close to the articular head of the humerus, and in the
same way the air may pass from bone to bone through every bone in the
fore limb. The hind limbs similarly receive air from the abdominal air
cell, which supplies the femur and other bones of the leg, the sacrum,
and the tail. But the joints of the backbone in front of the sacrum
receive their air from the cervical air sac. The air cells are not
limited to the bones, but ramify through the body, and in some cases
extend among the muscles. A bird may be said to breathe not only with
its lungs, but with its whole body. And it is even affirmed that
respiration has been carried on through a broken arm bone when the
throat was closed, and the bird under water.
Birds differ greatly in the extent to which the aircell system prolonged
from the lungs is developed, some having the air absent from every bone,
while others, like the Swift, are reputed to have air in every bone of
the body.
Comparison shows that in so far as the bones are the same in Bird and
Ornithosaur, the evidence of the air cells entering them extends to
resemblance, if not coincidence, in every detail. No living group of
animals except birds has pneumatic limb bones, in relation to the lungs;
so that it is reasonable to conclude that the identical structures in
the bones were due to the same cause in both the living and extinct
groups of animals. It is impossible to say that the lungs were identical
in Birds and Pterodactyles, but so far as evidence goes, there is no
ground for supposing them to have been different.
THE LUNGS OF REPTILES
[Illustration: FIG. 18. THE SIDE OF THE BODY OF A CHAMELEON
Ribs removed to show the sacculate branched form of the lung]
There is nothing comparable to birds, either in the lungs of living
reptiles or in their relation to the bones. The Chameleon is remarkable
in that the lung is not a simple bladder prolonged through the whole
length of the body cavity, as in a serpent, but it develops a number of
large lateral branches visible when the body is laid open. Except near
the trachaea, where the tissue has the usual density of a lizard lung,
the air cell is scarcely more complicated than the air bladder of a
fish, and does not enter into any bone of the skeleton. And although
many fishes like the Loach have the swim bladder surrounded by bone
connected with the head, it offers no analogy to the pneumatic condition
of the bones in the Pterodactyle.
THE FORM OF THE BRAIN CAVITY
[Illustration: FIG. 19. THE FORM OF THE BRAIN]
But the identity of the pneumatic foramina in Birds and Flying Reptiles
is not a character which stands by itself as evidence of organisation,
for a mould of the form of the brain case contributes evidence of
another structural condition which throws some light on the nature of
Ornithosaurs. Among many of the lower animals, such as turtles, the
brain does not fill the chamber in the dry skull, in which the same
bones are found as are moulded upon the brain in higher animals. For the
brain case in such reptiles is commonly an envelope of cartilage, as
among certain fishes; and except among serpents, the Ophidia, the bones
do not completely close the reptilian brain case in front. The brain
fills the brain case completely among birds. A mould from its interior
is almost as definite in displaying the several parts of which it is
formed as the actual brain would be. And the chief regions of the brain
in a bird--cerebrum, optic lobes, cerebellum--show singularly little
variation in proportion or position. The essential fact in a bird's
brain, which separates it absolutely from all other animals, is that the
pair of nerve masses known as the optic lobes are thrust out at the
sides, so that the large cerebral hemispheres extend partly over them as
they extend between them to abut against the cerebellum. This remarkable
condition has no parallel among other vertebrate animals. In Fishes,
Amphibians, Reptiles, and Mammals the linear succession of the several
parts of the brain is never departed from; and any appearance of
variation from it among mammals is more apparent than real, for the
linear succession may be seen in the young calf till the cerebral
hemispheres grow upward and lop backward, so as to hide the relatively
small brain masses which correspond to the optic lobes of reptiles,
extending over these corpora-quadrigemina, as they are named, so as to
cover more or less of the mass of the cerebellum. From these conditions
of the brain and skull, it would not be possible to mistake a mould
from the brain case of a bird for that of a reptile, though in some
conditions of preservation it is conceivable that the mould of the brain
of a bird might be distinguished with difficulty from that of the brain
in the lowest mammals. Taken by itself, the avian form of brain in an
animal would be as good evidence that its grade of organisation was that
of a bird as could be offered.
THE BRAIN IN SOLENHOFEN PTERODACTYLES
It happens that moulds of the brain of Pterodactyles, more or less
complete, are met with of all geological ages--Liassic, Oolitic, and
Cretaceous. The Solenhofen Slate is the only deposit in Europe in which
Pterodactyle skulls can be said to be fairly numerous. They commonly
have the bones so thin as to show the form of the upper surface of the
mould of the brain, or the bones have scaled off the mould, or remain in
the counterpart slab of stone, so as to lay bare the shape of the brain
mass.
In the Museum at Heidelberg a skull of this kind is seen in the
long-tailed genus of Pterodactyles named Rhamphorhynchus. It shows the
large rounded cerebral hemispheres, which extend in front of cerebral
masses of smaller size a little below them in position, which perhaps
are as like the brain of a monotreme mammal as a bird.
The short-tailed Pterodactylus described by Cuvier has the cerebral
hemispheres very similar to those of a bird, but the relations of the
hinder parts of the brain to each other are less clear.
The first specimen to show the back of the brain was found by Mr. John
Francis Walker, M.A., in the Cambridge Greensand. I was able to remove
the thick covering of cellular bone which originally extended above it,
and thus expose evidence that in the mutual relations of the fore and
hind parts of the brain bird and ornithosaur were practically identical.
Another Cambridge Greensand skull showed that in the genus
Ornithocheirus the optic lobes of the brain are developed laterally, as
in birds. That skull was isolated and imperfect. But about the same time
the late Rev. W. Fox, of Brixton, in the Isle of Wight, obtained from
Wealden beds another skull, with jaws, teeth, and the principal bones of
the skeleton, which showed that the Wealden Pterodactyle Ornithodesmus
had a similar and bird-like brain. In 1888 Mr. E. T. Newton, F.R.S.,
obtained a skull from the Upper Lias, uncrushed and free from
distortion. This made known the natural mould of the brain, which shows
the cerebral hemispheres, optic lobes, and cerebellum more distinctly
than in the specimens previously known. In some respects it recalls the
Heidelberg brain of Rhamphorhynchus in the apparently transverse
subdivision of the optic lobes, but it is unmistakably bird-like, and
quite unlike any reptile.
IMPORTANCE OF THE BRAIN AND BREATHING ORGANS
So far as the evidence goes, it appears that these fossil flying animals
show no substantial differences from birds, either in the mould of the
brain or the impress of the breathing organs upon the bones. These
approximations to birds of the nervous and respiratory systems, which
are beyond question two of the most important of the vital organs of an
animal, and distinctive beyond all others of birds, place the
naturalist in a singular dilemma. He must elect whether he will trust
his interpretation to the soft organs, which among existing animals
never vary their type in the great classes of vertebrate animals, and on
which the animal is defined as something distinct from its envelope the
skeleton and its appendages the limbs, or whether he will ignore them.
The answer must choose substantially between belief that the existing
order of Nature gives warrant for believing that these vital
characteristics which have been discussed might equally coexist with the
skeleton of a mammal or a reptile, as with that of a bird, for which
there is no particle of evidence in existing life. Or, as an
alternative, the fact must be accepted that birds only have such vital
organs as are here found, and therefore the skeleton, that may be
associated with them, cannot affect the reference of the type to the
same division of the animal kingdom as birds. The decision need not be
made without further consideration. But brain and breathing organs of
the avian type are structures of a different order of stability in most
animals from the bones, which vary to a remarkable extent in almost
every ordinal group of animals.
TEMPERATURE OF THE BLOOD
The organs of circulation and digestion are necessarily unknown. There
are reasons why the blood may have been hot, such as the evidences from
the wings of exceptional activity; though the temperature depends more
upon the amount of blood in the body than upon the apparatus by which it
is distributed. We speak of a Crocodile as cold-blooded, yet it is an
animal with a four-chambered heart not incomparable with that of a
bird. On the other hand, the Tunny, a sort of giant Mackerel, is a fish
with a three-chambered heart, only breathing the air dissolved in water,
which has blood as warm as a mammal, its temperature being compared to
that of a pig. Several fishes have blood as warm as that of Manis, the
scaly ant-eater; and many birds have hotter blood than mammals. The term
"hot-blooded," as distinct from "cold-blooded," applied to animals, is
relative to the arbitrary human standard of experience, and expresses no
more than the circumstance that mammals and birds are warmer animals
than reptiles and fishes.
The exceptional temperature of the Flying Fish has led to a vague
impression that physical activity and its effect upon the amount of
blood which vigour of movement circulates, are more important in raising
an animal's temperature than possession of the circulatory organs
commonly associated with hot blood, which drive the blood in distinct
courses through the body and breathing organs. Yet the kind of heart
which is always associated with vital structures such as Pterodactyles
are inferred to have possessed from the brain mould and the pneumatic
foramina in the bones, is the four-chambered heart of the bird and the
mammal. Considering these organs alone--of which the fossil bones yield
evidence--we might anticipate, by the law of known association of
structures, that nothing distinctly reptilian existed in the other soft
part of the vital organisation, because there is no evidence in favour
of or against such a possibility.
CHAPTER VIII
THE PLAN OF THE SKELETON
While these animals are incontestably nearer to birds than to any other
animals in their plan of organisation, thus far no proof has been found
that they are birds, or can be included in the same division of
vertebrate life with feathered animals. It is one of the oldest and
soundest teachings of Linnaeus that a bird is known by its feathers; and
the record is a blank as to any covering to the skin in Pterodactyles.
There is the strongest probability against feathers having existed such
as are known in the Archaeopteryx, because every Solenhofen Ornithosaur
appears to have the body devoid of visible or preservable covering,
while the two birds known from the Solenhofen Slate deposit are well
clothed with feathers in perfect preservation. We turn from the skin to
the skeleton.
The plan on which the skeleton is constructed remains as evidence of the
animal's place in nature, which is capable of affording demonstration on
which absolute reliance would have been placed, if the brain and
pneumatic foramina had remained undiscovered. With the entire skeleton
before us, it is inconceivable that anatomical science should fail to
discover the true nature of the animal to which it belonged, by the
method of comparing one animal with another. There is no lack of this
kind of evidence of Pterodactyles in the three or four scores of
skeletons, and thousands of isolated or associated bones, preserved in
the public museums of Europe and America.
I may recall the circumstance that the discovery of skeletons of fossil
animals has occasionally followed upon the interpretation of a single
fragment, from which the animal has been well defined, and sometimes
accurately drawn, before it was ever seen. So I propose, before drawing
any conclusions from the skeletons in the entirety of their
construction, to examine them bone by bone, and region by region, for
evidence that will manifest the nature of this brood of Dragons. Their
living kindred, and perhaps their extinct allies, assembled as a jury,
may be able to determine whether resemblances exist between them, and
whether such similarity between the bones as exists is a common
inheritance, or is a common acquisition due to similar ways of life, and
no evidence of the grade of the organism among vertebrate animals.
The bones of these Ornithosaurs, when found isolated, first have to be
separated from the organisms with which they are associated and mixed in
the geological strata. This discrimination is accomplished in the first
instance by means of the texture of the surface. The density and polish
of the bones is even more marked than in the bones of birds, and is
usually associated with a peculiar thinness of substance of the bone,
which is comparable to the condition in a bird, though usually a little
stouter, so that the bones resist crushing better. Pterodactyle bones
in many instances are recognised by their straightness and comparatively
uniform dimensions, due to the exceptional number of long bones which
enter into the structure of the wing as compared with birds. When the
bones are unerringly determined as Ornithosaurian, they are placed side
by side with all the bones which are most like them, till, judged by the
standard of the structures of living animals, the fossil is found to
show a composite construction as though it were not one animal but many,
while its individual bones often show equally composite characters, as
though parts of the corresponding bone in several animals had been
cunningly fitted together and moulded into shape.
THE PLAN OF THE HEAD IN ORNITHOSAURS
The head is always the most instructive part of an animal. It is less
than an inch long in the small Solenhofen skeleton named _Pterodactylus
brevirostris_, and is said to be three feet nine inches long in the
toothless Pterodactyle Ornithostoma from the Chalk of Kansas. Most of
these animals have a long, slender, conical form of head, tapering to
the point like the beak of a Heron, forming a long triangle when seen
from above or from the side. Sometimes the head is depressed in front,
with the beak flattened or rounded as in a Duck or Goose, and
occasionally in some Wealden and Greensand species the jaws are
truncated in front in a massive snout quite unlike any bird. The back of
the head is sometimes rounded as among birds, showing a smooth
pear-shaped posterior convexity in the region of the brain. Sometimes
the back of the head is square and vertical or oblique. Occasionally a
great crest of cellular tissue is extended backward from above the
brain case over the spines of the neck bones.
There are always from two to four lateral openings in the skull. First,
the nostril is nearest to the extremity of the beak. Secondly, the
orbits of the eyes are placed far backward. These two openings are
always present. The nostril may incline upward. The orbits of the eyes
are usually lateral, though their upper borders sometimes closely
approximate, as in the woodpecker-like types from the Solenhofen Slate
named _Pterodactylus Kochi_, now separated as another genus. In most
genera there is an opening in the side of the head, between the eye hole
and the nostril, known as the antorbital vacuity; and another opening,
which is variable in size and known as the temporal vacuity, is placed
behind the eye. The former is common in the skulls of birds, the latter
is absent from all birds and found in many reptiles.
The palate is usually imperfectly seen, but English and American
specimens have shown that it has much in common with the palate in
birds, though it varies greatly in form of the bones in representatives
from the Lias, Oolites, and Cretaceous rocks.
From the scientific aspect the relative size of the head, its form, and
the positions and dimensions of its apertures and processes, are of
little importance in comparison with its plan of construction, as
evidenced by the positions and relations to each other of the bones of
which it is formed. There usually is some difficulty in stating the
limits of the bones of the skull, because in Pterodactyles, as among
birds, they usually blend together, so that in the adult animal the
sutures between the bones are commonly obliterated.
Bones have relations to each other and places in the head which can only
change as the organs with which they are associated change their
positions. No matter what the position of a nostril may be--at the
extremity of a long snout, as in an ant-eater, or far back at the top of
the head in a porpoise, or at the side of the head in a bird--it is
always bordered by substantially the same bones, which vary in length
and size with the changing place of the nostril and the form of the
head. Every region of the head is defined by this method of
construction; so that eye holes and nose holes, brain case and jaw
bones, palate and teeth, beak, and back of the skull are all instructive
to those who seek out the life-history of these animals. We may briefly
examine the head of an Ornithosaurian.
BONES ABOUT THE NOSTRIL
No matter what its form may be, the head of an Ornithosaur always
terminates in front in a single bone called the intermaxillary. It sends
a bar of bone backward above the visible nostrils, between them; and a
bar on each side forms the margin of the jaw in which teeth are
implanted. The bone varies in depth, length, sharpness, bluntness,
slenderness, and massiveness. As the bone becomes long the jaw is
compressed from side to side, and the openings of the nostrils are
removed backward to an increasing distance from the extremity of the
beak.
The outer and hinder border of the nostril is made by another bone named
the maxillary bone, which is usually much shorter than the premaxillary.
It contains the hindermost teeth, which rarely differ from those in
front, except in sometimes being smaller.
The nasal bones, which always make the upper and hinder border of the
nostrils, meet each other above them, in the middle line of the beak.
[Illustration: FIG. 20
Showing that the extremity of the jaws in Rhamphorhynchus was
sheathed in horn as in the giant Kingfisher, since the jaws
similarly gape in front.
The hyoid bones are below the lower jaw in the Pterodactyle.]
The nostrils are unusually large in the Lias genus named Dimorphodon,
and small in species of the genus Rhamphorhynchus from Solenhofen. Such
differences result from the relative dimensions and proportions of these
three bones which margin the nasal vacuity, and by varying growth of
their front margins or of their hinder margins govern the form of the
snout.
The jaws are most massive in the genera known from the Wealden beds to
the Chalk. The palatal surface is commonly flat or convex, and often
marked by an elevated median ridge which corresponds to a groove in the
lower jaw, though the median ridge sometimes divides the palate into two
parallel concave channels. The jaw is margined with teeth which are
rarely fewer than ten or more than twenty on each side. They are sharp,
compressed from side to side, curved inward, and never have a saw-like
edge on the back and front margins. No teeth occur upon the bones of the
palate.
In most birds there is a large vacuity in the side of the head between
the nostril and the orbit of the eye, partly separated from it by the
bone which carries the duct for tears named the lachrymal bone. The same
preorbital vacuity is present in all long-tailed Pterodactyles, though
it is either less completely defined or absent in the group with short
tails. It affords excellent distinctive characters for defining the
genera. In the long-tailed genus Scaphognathus from Solenhofen this
preorbital opening is much larger than the nostril, while in Dimorphodon
these vacuities are of about equal size. Rhamphorhynchus is
distinguished by the small size of the antorbital vacuity, which is
placed lower than the nostril on the side of the face. The aperture is
always imperfectly defined in Pterodactylus, and is a relatively small
vacuity compared with the long nostril. In Ptenodracon the antorbital
vacuity appears to have no existence separate from the nostril which
adjoins the eye hole. And so far as is known at present there is no
lateral opening in advance of the eye in the skull in any Ornithosaur
from Cretaceous rocks, though the toothless Ornithostoma is the only
genus with the skull complete. When a separate antorbital vacuity
exists, it is bordered by the maxillary bone in front, and by the malar
bone behind. The prefrontal bone is at its upper angle. That bone is
known in a separate state in reptiles and, I think, in monotreme
mammals. Its identity is soon lost in the mammal, and its function in
the skull is different from the corresponding bone in Pterodactyles.
BONES ABOUT THE EYES
[Illustration: FIG. 21. UPPER SURFACE OF SKULL OF THE HERON
Compared with the same aspect of the skull of Rhamphorhynchus]
The third opening in the side of the head, counting from before
backward, is the orbit of the eye. In this vacuity is often seen the
sclerotic circle of overlapping bones formed in the external membrane of
the eye, like those in nocturnal birds and some reptiles. The eye hole
varies in form from an inverted pear-shape to an oblique or transverse
oval, or a nearly circular outline. It is margined by the frontal bone
above; the tear bone or lachrymal, and the malar or cheek bone in front;
while the bones behind appear to be the quadrato-jugal and post-frontal
bones, though the bones about the eye are somewhat differently arranged
in different genera.
The eyes were frequently, if not always, in contact with the anterior
walls of the brain case, as in many birds, and are always far back in
the side of the head. In Dimorphodon they are in front of the
articulation of the lower jaw; in Rhamphorhynchus, above that
articulation; while in Ornithostoma they are behind the articulation for
the jaw. This change is governed by the position of the quadrate bone,
which is vertical in the Lias genus, inclined obliquely forward in the
fossils from the Oolites, and so much inclined in the Chalk fossil that
the small orbit is thrown relatively further back.
Thus far the chief difference in the Pterodactyle skull from that of a
bird is in the way in which the malar arch is prolonged backward on each
side. It is a slender bar of bone in birds, without contributing
ascending processes to border vacuities in the side of the face, while
in these fossil animals the lateral openings are partly separated by the
ascending processes of these bones. This divergence from birds, in the
malar bone entering the orbit of the eye is approximated to among
reptiles and mammals, though the conditions, and perhaps the presence of
a bone like the post-orbital bone, are paralleled only among Reptiles.
The Pterodactyles differ among themselves enough for the head to make a
near approach to Reptiles in Dimorphodon, and to Birds in
Pterodactylus. In the Ground Hornbill and the Shoebill the lachrymal
bones in front of the orbits of the eyes grow down to meet the malar
bars without uniting with them. The post-frontal region also is
prolonged downward almost as far as the malar bar, as though to show
that a bird might have its orbital circle formed in the same way and by
the same bones as in Pterodactylus. Cretaceous Ornithosaurs sometimes
differ from birds apparently in admitting the quadrato-jugal bone into
the orbit. It then becomes an expanded plate, instead of a slender bar
as in all birds.
THE TEMPORAL FOSSA
A fourth vacuity is known as the temporal fossa. When the skull of such
a mammal as a Rabbit, or Sheep, is seen from above, there is a vacuity
behind the orbits for the eyes, which in life is occupied by the muscles
which work the lower jaw. It is made by the malar bone extending from
the back of the orbit and the process of bone, called the zygomatic
process, extending forward from the articulation of the jaw, which
arches out to meet the malar bone.
In birds there is no conspicuous temporal fossa, because the malar bar
is a slender rod of bone in a line with the lower end of the quadrate
bone.
Reptile skulls have sometimes one temporal vacuity on each side, as
among tortoises, formed by a single lateral bar. These vacuities, which
correspond to those of mammals in position, are seen from the top of the
head, as lateral vacuities behind the orbits of the eyes, and are termed
superior temporal vacuities. In addition to these there is often in
other reptiles a lateral opening behind the eye, termed the inferior
temporal vacuity, seen in Crocodiles, in Hatteria, and in Lizards; and
in such skulls there are two temporal bars seen in side view,
distinguished as superior and inferior. The superior arch always
includes the squamosal bone, which is at the back of the single bar in
mammals. The lower arch includes the malar bone, which is in front in
the single arch of mammals. The circumstance that both these arches are
connected with the quadrate bone makes the double temporal arch
eminently reptilian.
In Ornithosaurs the lateral temporal vacuity varies from a typically
reptilian condition to one which, without becoming avian, approaches the
bird type. In skulls from the Lias, Dimorphodon and Campylognathus,
there is a close parallel to the living New Zealand reptile Hatteria, in
the vertical position of the quadrate bone and in the large size of the
vacuity behind and below the eye, which extends nearly the height of the
skull. In the species of the genus Pterodactylus, the forward
inclination of the quadrate bone recalls the Curlew, Snipe, and other
birds. The back of the head is rounded, and the squamosal bone, which
appears to enter into the wall of the brain case as in birds and
mammals, is produced more outward than in birds, but less than in
mammals, so as to contribute a little to the arch which is in the
position of the post-frontal bone of reptiles. It is triangular, and
stretches from the outer angle of the frontal bone at the back of the
orbit to the squamosal behind, where it also meets the quadrate bone.
Its third lower branch meets the quadratojugal, which rests upon the
front of the quadrate bone, as in Iguanodon, and is unlike Dimorphodon
in its connexions. In that genus the supra-temporal bone, or
post-orbital bone, appears to rest upon the post-frontal and connect it
with the quadrato-jugal. In Dimorphodon the malar bone is entirely
removed from the quadrate, but in Pterodactylus it meets its articular
end. Between the post-frontal bone above and the quadrato-jugal bone
below is a small lunate opening, which represents the lateral temporal
vacuity; and so far, this is a reptilian character. But if the thin
post-frontal bone were absorbed, Pterodactylus would resemble birds.
There is no evidence that the quadrate bone is free in any Ornithosaurs,
as it is in all birds, while in Dimorphodon it unites by suture with the
squamosal bone. In Ornithostoma the lateral temporal vacuity is little
more than a slit between the quadrate bone below, the quadrato-jugal in
front, and what may be the post-frontal bone behind (see Fig. 2, p. 12).
BONES ABOUT THE BRAIN
The bones containing the brain appear to be the same as form the brain
case in birds. The form of the back of the skull varies in two ways.
First it may be flat above and flat at the back, when the back of the
head appears to be square. This condition is seen in all the long-tailed
genera, such as Campylognathus from the Lias and Rhamphorhynchus, and is
associated with a high position for the upper temporal bar. Secondly,
the back of the head may be rounded convexly, both above and behind.
That condition is seen in the short-tailed genera, such as
Pterodactylus. But in the large Cretaceous types, such as Ornithocheirus
and Ornithostoma, the superior longitudinal ridge which runs back in
the middle line of the face becomes elevated and compressed from side to
side at the back of the head as a narrow deep crest, prolonged backward
over the neck vertebrae for some inches of length. All these three types
are paralleled more or less in birds which have the back of the head
square like the Heron, or rounded like the Woodpecker; or crested,
though the crest of the Cormorant is not quite identical with
Ornithocheirus, being a distinct bone at the back of the head in the
bird which never blends with the skull. In so far as the crest is
reptilian it suggests the remarkable crest of the Chameleon. In the
structure of the back of the skull the bones are a modification of the
reptilian type of Hatteria in the Lias genus Campylognathus, but the
reptilian characters appear to be lost in the less perfectly preserved
skulls of Cretaceous genera.
The palate is well known in the chief groups of Ornithosaurs, such as
Campylognathus, Scaphognathus, and Cycnorhamphus.
Mr. E. T. Newton, F.R.S., has shown that in the English skull from the
Lias of Whitby, the forms of the bones are similar to the palate in
birds and unlike the conditions in reptiles. There is one feature,
however, which may indicate a resemblance to Dicynodon and other fossil
reptiles from South Africa. A slender bone extends from the base of the
brain case, named the basi-sphenoid bone, outward and forward to the
inner margin of the quadrate bone (Fig. 22). A bone is found thus placed
in those South African Reptiles, which show many resemblances to the
Monotreme and Marsupial Mammals. It is not an ordinary element of the
skeleton and is unknown in living animals of any kind in that position.
It has been thought possible that it may represent one of the bones
which among mammals are diminutive and are included in the internal ear.
The resemblance may have some interest hereafter, as helping to show
that certain affinities of the Ornithosaurs may lie outside the groups
of existing reptiles. Instead of being directed transversely outward, as
in the palatal region of _Dicynodon lacerticeps_, they diverge outward
and forward to the inner border of the articulation for the lower jaw
which is upon the quadrate bone.
[Illustration: FIG. 22]
BONES OF THE PALATE
There is a pair of bones which extend forward from these inner articular
borders of the quadrate bones, and converge in a long #V#-shape till
they merge in the hard palate formed by the bones of the front of the
beak, named intermaxillary and maxillary bones. The limits of the bones
of the palate are not distinct, but there can be no doubt that the
front of the #V# is the bone named vomer, that the palatine bones are at
its sides, and that its hinder parts are the pterygoid bones as in
birds. There is a long, wide, four-sided, open space in the middle of
the palate, between the vomer and the basi-sphenoid bone, unlike
anything in birds or other animals.
Professor Marsh, in a figure of the palate in the great skull of the
toothless Pterodactyle named Ornithostoma (Pteranodon), from the Chalk
of Kansas, found a large oval vacuity in this region of the palate. In
that genus the pterygoid bones meet each other between the quadrate
bones as in Dicynodon (Fig. 73, p. 182). Hence the great palatal vacuity
here seen in the Ornithosaur is paralleled by the small vacuity in the
South African reptile, which is sometimes distinct and sometimes partly
separated from the anterior part of the vacuity which forms the openings
of the nostrils on the palate.
The Solenhofen skulls which give any evidence of the palate are exposed
in side view only, and the bones, imperfectly seen through the lateral
vacuities, are displaced by crushing. They include long strips like the
vomerine bones in the Lias fossil, and they diverge in the same way as
they extend back to the quadrate bones. The oblique division into vomer
in front and pterygoid bone behind is shown by Goldfuss in his original
figure of Scaphognathus. Thus there is some reason for believing that
all Ornithosaurs have the palate formed upon the same general plan,
which is on the whole peculiar to the group, especially in not having
the palatal openings of the nares divided in the middle line. It would
appear probable that the short-tailed animals have the pterygoid bones
meeting in the middle line and triangular; and that they are slender
rods entirely separate from each other in the long-tailed genera.
THE TEETH
The teeth are all of pointed, elongated shape, without distinction into
the kinds seen in most mammals and named incisors, canines, and
grinders. They are organs for grasping, like the teeth of the
fish-eating Crocodile of India, and are not unlike the simple teeth of
some Porpoises. They are often implanted in oblique oval sockets with
raised borders, usually at some distance apart from each other, and have
the crown pointed, flattened more on the outer side than on the inner
side, usually directed forward and curved inward. As in many extinct
animals allied to existing reptiles, the teeth are reproduced by germs,
which originate on the inner side of the root and grow till they
gradually absorb the substance of the old tooth, forming a new one in
its place. Frequently in Solenhofen genera, like Scaphognathus and
Pterodactylus, the successional tooth is seen in the jaw on the hinder
border of the tooth in use. There is some variation in the character of
bluntness or sharpness of the crowns in the different genera, and in
their size.
The name Dimorphodon, given to the animal from the Lias of Lyme Regis,
expresses the fact that the teeth are of two kinds. In the front of the
jaw three or four large long teeth are found in the intermaxillary bone
on each side, as in some Plesiosaurs, while the teeth found further back
in the maxillary bone are smaller, and directed more vertically
downward. This difference is more marked in the lower jaw than in the
upper jaw. In Rhamphorhynchus the teeth are all relatively long and
large, and directed obliquely forward, but absent from the extremities
of the beak, as in the German genus from the Lias named Dorygnathus, in
which the bone of the lower jaw (which alone is known) terminates in a
compressed spear. In Scaphognathus the teeth are few, more vertical, and
do not extend backward so far as in Rhamphorhynchus, but are carried
forward to the extremity of the blunt, deep jaw.
In the short-tailed Pterodactyles the teeth are smaller, shorter, wider
at the base of the crown, closer together, and do not extend so far
backward in the jaw. In Ornithocheirus two teeth always project forward
from the front of the jaw. Ornithostoma is toothless.
SUPPOSED HORNY BEAK
Sometimes a horny covering has been suggested for the beak, like that
seen in birds or turtles, but no such structure has been preserved, even
in the Solenhofen Slate, in which such a structure would seem as likely
to be preserved as a wing membrane, though there is one doubtful
exception. There are marks of fine blood vessels on some of the jaws,
indicating a tough covering to the bone. In Rhamphorhynchus the jaws
appear to gape towards their extremities as though the interspace had
originally been occupied by organic substance like a horny beak.
LOWER JAW
The lower jaw varies in relative length with the vertical or horizontal
position of the quadrate bone in the skull. In Dimorphodon the jaw is as
long as the skull; but in the genera from the Oolitic rocks the
mandible is somewhat shorter, and in Ornithostoma the discrepancy
reaches its maximum. The hinder part of the jaw is never prolonged
backward much beyond the articulation, differing in this respect from
Crocodiles and Plesiosaurs.
The depth of the jaw varies. It is slender in Pterodactylus, and is
probably stronger relatively to the skull in Scaphognathus than in any
other form. It fits between the teeth and bones of the alveolar border
in the skull, in all the genera. In Dimorphodon its hinder border is
partly covered by the descending edge of the malar process which these
animals develop in common with some Dinosaurs, and some Anomodont
reptiles, and many of the lower mammals. In this hinder region the lower
jaw is sometimes perforated, in the same way as in Crocodiles. That
condition is observed in Dimorphodon, but is not found in Pterodactylus.
The lower jaw is always composite, being formed by several bones, as
among reptiles and birds. The teeth are in the dentary bone or bones,
and these bones are almost always blended as in most birds and Turtles,
and not separate from each other as among Crocodiles, Lizards, and
Serpents.
An interesting contour for the lower border of the jaw is seen in
Ornithostoma, as made known in figures of American examples by
Professors Marsh and Williston. It deepens as it extends backwards for
two-thirds its length, stops at an angle, and then the depth diminishes
to the articulation with the skull. This angle of the lower jaw is a
characteristic feature of the jaws of Mammals. It is seen in the
monotreme Echidna, and is characteristic of some Theriodont Reptiles
from South Africa, which in many ways resemble Mammals. The character
is not seen in the jaws of specimens from the Oolitic rocks, but is
developed in the toothed Ornithocheirus from the Cambridge Greensand,
and is absent from the jaws of existing reptiles and birds.
[Illustration: FIG. 23 COMPARISON OF THE LOWER JAW IN ECHIDNA AND
ORNITHOSTOMA]
SUMMARY OF CHARACTERS OF THE HEAD
Taken as a whole, the head differs from other types of animals in a
blending of characters which at the present day are found among Birds
and Reptiles, with some structures which occur in extinct groups of
animals with similar affinities, and perhaps a slight indication of
features common to the lowest mammals. It is chiefly upon the head that
the diverse views of earlier writers have been based. Cuvier was
impressed with the reptilian aspect of the teeth; but in later times
discoveries were made of Birds with teeth--Archaeopteryx, Ichthyornis,
Hesperornis. The teeth are quite reptilian, being not unlike miniature
teeth of Mosasaurus. If those birds had been found prior to the
discovery of Pterodactyles, the teeth might have been regarded as a link
with the more ancient birds, rather than a crucial difference between
birds and reptiles.
All the specimens show a lateral temporal hole in the bones behind the
eye, and this is found in no bird or mammal, and is typical of such
reptiles as Hatteria. The quadrate bone may not be so decisive as Cuvier
thought it to be, for its form is not unlike the quadrate of a bird, and
different, so far as I have seen, from that of living reptiles. This
region of the head is reptilian, and if it occurred in a bird the
character would be as astonishing as was the discovery of teeth in
extinct birds. These characters of the head are also found in fossil
animals named Dinosaurs, in association with many resemblances to birds
in their bones.
The palate might conceivably be derived from that of Hatteria by
enlarging the small opening in the middle line in that reptile till it
extended forward between the vomera; but it is more easily compared with
a bird, which the animal resembles in its beak, and in the position of
the nares. Excepting certain Lizards, all true existing Reptiles have
the nostrils far forward and bordered by two premaxillary bones instead
of one intermaxillary, as in Birds and Ornithosaurs. If nothing were
known of the animal but its head bones, it would be placed between
Reptiles and Birds.
CHAPTER IX
THE BACKBONE, OR VERTEBRAL COLUMN
The backbone is a more deep-seated part of the skeleton than the head.
It is more protected by its position, and has less varied functions to
perform. Therefore it varies less in distinctive character within the
limits of each of the classes of vertebrate animals than either the head
or limbs. It is divided into neck bones, the cervical vertebrae; back
bones, the dorsal vertebrae; loin bones, the lumbar vertebrae; the sacrum,
or sacral vertebrae, which support the hind limbs; and the tail. Of these
parts the tail is the least important, though it reaches a length in
existing reptiles which sometimes exceeds the whole of the remainder of
the body, and includes hundreds of vertebrae. It attains its maximum
among serpents and lizards. In frogs it is practically absent. In some
of the higher mammals it is a rudiment, which does not extend beyond the
soft parts of the body.
THE NECK
The neck is more liable to vary than the back, with the habit of life of
the animal. And although mammals almost always preserve the same number
of seven bones in the neck, the bones vary in length between the short
condition of the porpoise, in which the neck is almost lost, and the
long bones which form the neck of the Llama, though even these may be
exceeded by some fossil reptiles like Tanystrophoeus. In many mammals
the neck bones do not differ in length or size from those of the back.
In others, like the Horse and Ox, they are much broader and larger.
There is the same sort of variation in the bones of the neck among
birds, some being slender like the Heron, others broad like the Swan.
But there is also a singular variation in number of vertebral bones in a
bird's neck. At fewest there are nine, which equals the exceptionally
large number found among mammals in the neck of one of the Sloths.
Usually birds have ten to fifteen cervical vertebrae, and in the Swan
there are twenty-three. Most of the neck bones of birds are relatively
long, and the length of the neck is often greater than the remainder of
the vertebral column.
Reptiles usually have short necks. The common Turtle has eight bones in
the neck, ten in the back. The two regions are sharply defined by the
dorsal shield. Their articular ends are sometimes cupped in front, in
the neck, sometimes cupped behind, or convex at both ends, or even
flattened, or the articulation may be made exceptionally by the neural
arch alone. Nine is the largest number of neck bones in existing
Lizards, and there are usually nine in Crocodiles; so that reptiles
closely approach mammals in number of the neck bones. It is remarkable
that the maximum number in a mammal and in living reptiles should
coincide with the minimum number in birds. Therefore the number of
cervical vertebrae as an attribute of Mammal, Bird, or Reptile, can only
be important from its constancy.
German naturalists affirm on clear evidence that the Solenhofen
Pterodactyles have seven cervical vertebrae. In many specimens there can
be no doubt about the number, because the neck bones are easily
distinguished from those of the back by their size; but the number is
not always easy to count.
As in Birds, the first vertebra, or atlas, in Pterodactyles is extremely
short, and is generally--if not always--blended with the much longer
second vertebra, named the axis. The front of the atlas forms a small
rounded cup to articulate with the rounded ball of the basioccipital
bone at the back of the skull. The third and fourth vertebrae are longer,
but the length visibly shortens in the sixth and seventh.
Sometimes the vertebrae are slender and devoid of strong spinous
processes. This is the condition in the little _Pterodactylus
longirostris_ and in the comparatively large _Cycnorhamphus Fraasii_, in
which there is a slight median ridge along the upper surface of the arch
of the vertebra. This condition is paralleled in birds with long necks,
especially wading birds such as the Heron. Other Ornithosaurs, such as
Ornithocheirus from the Cretaceous rocks, have the neck much more
massive. The vertebrae are flattened on the under side. The arch above
the nervous matter of the spinal cord has a more or less considerable
transverse expansion, and may even be as wide as long. These vertebrae
have proportions and form such as may be seen in Vultures or in the
Swan. In either case the form of the neck bones is more or less
bird-like, and the neural spine may be elevated, especially in
Pterodactyles with long tails.
One of the most distinctive features of the neck bones of a bird is the
way in which the cervical ribs are blended with the vertebrae. They are
small, and each is often prolonged in a needle-like rod at the side of
the neck bone.
In Ornithocheirus the cervical rib similarly blends with the vertebra by
two articulations, as in mammals, so that it might escape notice but for
the channel of a blood vessel which is thus inclosed. In several of the
older Pterodactyles from Solenhofen the ribs of the neck vertebrae remain
separated, as in a Crocodile, though still bird-like in their form,
anterior position, and mode of attachment. In Terrapins and Tortoises
the long neck vertebrae have no cervical ribs.
[Illustration: FIG. 24 UNITED ATLAS AND AXIS OF ORNITHOCHEIRUS
(Cambridge Greensand)]
The articular surfaces between the bodies of the vertebrae, in the neck,
are transversely oval. The middle part of this articular joint is made
by the body of the vertebra; its outer parts are in the neural arch. In
front this surface is a hollow channel, often more depressed than in any
other animals. The corresponding surface behind is convex, with a
process on each side at its lower outer angles (Fig. 25). It is a
modification of the cup-and-ball form of vertebral articulation, which
at the present day is eminently reptilian. Serpents and Crocodiles have
the articulations similarly vertical, but in both the form of the
articulation is a circle. In Lizards the articular cup is usually rather
wider than deep, when the cup and ball are developed in the vertebrae; it
differs from the vertical condition in pterodactyles in being oblique
and much narrower from side to side. Only among Crocodiles and Hatteria
is there a double articulation for the cervical rib, though in neither
order have rib or vertebra in the neck the bird-like proportions which
are usual in these animals. Pterodactyles show no resemblance to birds
in this vertebral articulation. A Bird has the corresponding surface
concave from side to side in front, but it is also convex from above
downward, producing what is known as the saddle-shaped form which is
peculiarly avian, being found in existing birds except in part of the
back in Penguins. It is faintly approximated to in one or two neck
vertebrae in man. Professor Williston remarks that in the toothless
Pterodactyles of Kansas the hinder ball of the vertebral articulation is
continued downward and outward as a concave articulation upon the
processes at its outer corners. There are no mammals with a cup-and-ball
articulation between the vertebrae, so that for what it is worth the
character now described in Ornithosaurs is reptilian, when judged by
comparison with existing animals.
[Illustration: FIG. 25. CERVICAL VERTEBRA OF ORNITHOCHEIRUS
From the Cambridge Greensand]
Low down on each side of the vertebra, at the junction of its body with
the neural arch, is a large ovate foramen, transversely elongated, and
often a little impressed at the border, which is the entrance of the
air cell into the bone. These foramina are often one-third of the length
of the neck vertebrae in specimens from the Cambridge Greensand, where
the neck bones vary from three-quarters of an inch to about two and a
half inches in length, and in extreme forms are as wide as long. The
width of the interspace between the foramina is one-half the width of
the vertebrae, though this character varies with different genera and
species. Several species from the Solenhofen Slate have the neck long
and slender, on the type of the Flamingo. In others the neck is thick
and short--in the _Scaphognathus crassirostris_ and _Pterodactylus
spectabilis_. Some genera with slender necks have the bones preserved
with a curved contour, such as might suggest a neck carried like that of
a Llama or a Camel. The neck is occasionally preserved in a curve like a
capital #S#, as though about to be darted forward like that of a bird in
the act of striking its prey. The genera of Pterodactyles with short
necks may have had as great mobility of neck as is found among birds
named Ducks and Divers; but those Pterodactyles with stout necks, such
as Dimorphodon and Ornithocheirus, in which the vertebrae are large,
appear to have been built more for strength than activity, and the neck
bones have been chiefly concerned in the muscular effort to use the
fighting power of the jaws in the best way.
THE BACK
The region of the back in a Pterodactyle is short as compared with the
neck, and relatively is never longer than the corresponding region in a
bird. The shortness results partly from the short length of the
vertebrae, each of which is about as long as wide. There is also a
moderate number of bones in the back. In most skeletons from Solenhofen
these vertebrae between the neck and girdle of hip bones number from
twelve to sixteen. They have a general resemblance in form to the dorsal
vertebrae in birds. The greatest number of such vertebrae in birds is
eleven. The number is small because some of the later vertebrae in birds
are overlapped by the bones of the hip girdle, which extend forward and
cover them at the sides, so that they become blended with the sacrum.
This region of the skeleton in the Dimorphodon from the Lias is
remarkable for the length of the median process, named the neural spine,
which is prolonged upward like the spines of the early dorsal vertebrae
of Horses, Deer, and other mammals. In this character they differ from
living reptiles, and parallel some Dinosaurs from the Weald. The bones
of the back in Ornithocheirus from the Cambridge Greensand show the
under side to be well rounded, so that the articular surfaces between
the vertebrae, though still rather wider than deep, are much less
depressed than in the region of the neck. The neural canal for the
spinal cord has become larger and higher, and the sides of the bone are
somewhat compressed. Strong transverse processes for the support of the
ribs are elevated above the level of the neural canal, at the sides of
vertebrae compressed on the under sides, and directed outward. Between
these lateral horizontal platforms is the compressed median neural
spine, which varies in vertical height. The articulation of the ribs is
not seen clearly. Isolated ribs from the Stonesfield Slate have
double-headed dorsal ribs, like those of birds. In some specimens from
the Solenhofen Slate like the Scaphognathus, in the University Museum at
Bonn, dorsal ribs appear to be attached by a notch in the transverse
process of the dorsal vertebra, which resembles the condition in
Crocodiles. Variations in the mode of attachment of ribs among mammals
may show that character to be of subordinate importance. Von Meyer has
described the first pair of ribs as frequently larger than the others,
and there appear in Rhamphorhynchus to be examples preserved of the
sternal ribs, which connect the dorsal ribs with the sternum. Six pairs
have been counted. A more interesting feature in the ribs consists in
the presence behind the sternum, which is shorter than the corresponding
bone in most birds, of median sternal ribs. They are slender #V#-shaped
bones in the middle line of the abdomen, which overlapped the ends of
the dorsal ribs like the similar sternal bones of reptiles. Such
structures are unknown among Birds and Mammals. There is no trace in the
dorsal ribs of the claw-like process, which extends laterally from rib
to rib as a marked feature in many birds. Its presence or absence may
not be important, because it is represented by fibro-cartilage in the
ribs of crocodiles, and may be a small cartilage near the head of the
rib in serpents, and is only ossified in some ribs of the New Zealand
reptile Hatteria. So that it might have been present in a fossil animal
without being ossified and preserved. Although the structure is
associated with birds, it is possibly also represented by the great bony
plates which cover the ribs in Chelonians, and combine to form the
shield which covers the turtle's back. The structure is as
characteristic of reptiles as of birds, but is not necessarily
associated with either.
[Illustration: FIG. 26
The upper figures show the side and back of a dorsal vertebra of
Ornithocheirus compared with corresponding views of the side and
back of a dorsal vertebra of a Crocodile]
There are two remarkable modifications of the early dorsal vertebrae in
some of the Cretaceous Pterodactyles. First, in the genus Ornithodesmus
from the Weald the early dorsal vertebrae are blended together into a
continuous mass, like that which is found in the corresponding region of
the living Frigate-bird, only more consolidated, and similar to that
consolidated structure found behind the dorsal vertebrae, known as the
sacrum, made by the blending of the vertebrae into a solid mass which
supports the hip bones. Secondly, in some of the Cretaceous genera of
Pterodactyles of Europe and America the vertebrae in the front part of
the back are similarly blended, but their union is less complete; and in
genera Ornithocheirus and Ornithostoma--the former chiefly English, the
latter chiefly American--the sides of the neural spines are flattened to
form an oval articular surface on each side, which gives attachment to
the flattened ends of their shoulder-blade bones named the scapulae. This
condition is found in no other animals. Three vertebrae appear to have
their neural arches thus united together. The structure so formed may be
named the notarium to distinguish it from the sacrum.
SACRUM
For some mysterious reason the part of the backbone which lies between
the bones of the hips and supports them is termed the sacrum. Among
living reptiles the number of vertebrae in this region is usually two, as
in lizards and crocodiles. There are other groups of fossil reptiles in
which the number of sacral vertebrae is in some cases less and in other
cases more. There is, perhaps, no group in which the sacrum makes a
nearer approach to that of birds than is found among these
Pterodactyles, although there are more sacral vertebrae in some
Dinosaurs. In birds the sacral vertebrae number from five to twenty-two.
In bats the number is from five to six. In some Solenhofen species, such
as _Pterodactylus dubius_ and _P. Kochi_ and _P. grandipelvis_, the
number is usually five or six. The vertebrae are completely blended. The
pneumatic foramina in the sacrum, so far as they have been observed, are
on the under sides of the transverse processes; while in the
corresponding notarial structure in the shoulder girdle the foramina are
in front of the transverse processes. Almost any placental mammal in
which the vertebrae of the sacral region are anchylosed together has a
similar sacrum, which differs from that of birds in the more complete
individuality of the constituent bones remaining evident. The transverse
processes in front of the sacrum are wider than in its hinder part; so
that the pelvic bones which are attached to it converge as they extend
backward, as among mammals. The bodies of the vertebrae forming the
sacrum are similar in length to those of the back. Each transverse
process is given off opposite the body of its own vertebra, but from a
lower lateral position than in the region of the back, in which the
vertebrae are free.
[Illustration: FIG. 27. SACRUM OF RHAMPHORHYNCHUS
Showing the complete blending of the vertebrae and ribs as in a bird,
with the well-defined Iliac bones, produced chiefly in front of the
acetabulum for the head of the femur.]
The hip bones are closely united with the sacrum by bony union, and
rarely appear to come away from the sacral vertebrae, as among mammals
and reptiles, though this happens with the Lias Pterodactyles. In the
Stonesfield Slate and Solenhofen Slate the slender transverse processes
from the vertebrae blend with the ilium of the hip girdle, and form a
series of transverse foramina on each side of the bodies of the
vertebrae. In the Cambridge Greensand genera the part of the ilium above
the acetabulum for the articular head of the femur appears to be always
broken away, so that the relation of the sacrum to the pelvis has not
been observed. This character is no mark of affinity, but only shows
that ossification obliterated sutures among these animals in the same
way as among birds.
The great difference between the sacrum of a Pterodactyle and that of a
bird has been rendered intelligible by the excellent discussion of the
sacral region in birds made by Professor Huxley. He showed that it is
only the middle part of the sacrum of a chicken which corresponds to the
true sacrum of a reptile, and comprises the five shortest of the
vertebrae; while the four in front correspond to those of the lower part
of the back, which either bear no ribs or very short ribs, and are known
as the lumbar region in mammals, so that the lower part of the back
becomes blended with the sacrum, and thus reduces the number of dorsal
vertebrae. Similarly the five vertebrae which follow the true sacral
vertebrae are originally part of the tail, and have been blended with the
other vertebrae in front, in consequence of the extension along them of
the bird's hip bones. This interpretation helps to account for the great
length of the sacrum in many birds, and also explains in part the
singular shortness of the tail in existing birds. The Ornithosaur sacrum
has neither the lumbar nor the caudal portions of the sacrum of a bird.
THE TAIL
The tail is perhaps the least important part of the skeleton, since it
varies in character and length in different genera. The short tails seen
in typical pterodactyles include as few as ten vertebrae in
_Pterodactylus grandipelvis_ and _P. Kochi_, and as many as fifteen
vertebrae in _Pterodactylus longirostris_. The tails are more like those
of mammals than existing birds, in which there are usually from six to
ten vertebrae terminating in the ploughshare bone. But just as some
fossil birds, like the Archaeopteryx, have about twenty long and slender
vertebrae in the tail, so in the pterodactyle Rhamphorhynchus this region
becomes greatly extended, and includes from thirty-eight to forty
vertebrae. In Dimorphodon the tail vertebrae are slightly fewer. The
earliest are very short, and then they become elongated to two or three
times the length of the early tail vertebrae, and finally shorten again
towards the extremity of the tail, where the bones are very slender. In
all long-tailed Ornithosaurians the vertebrae are supported and bordered
by slender ossified ligaments, which extend like threads down the tail,
just as they do in Rats and many other mammals and in some lizards.
Professor Marsh was able to show that the extremity of the tail in
Rhamphorhynchus sometimes expands into a strong terminal caudal membrane
of four-sided somewhat rhomboidal shape. He regards this membrane as
having been placed vertically. It is supported by delicate processes
which represent the neural spines of the vertebrae prolonged upward. They
are about fifteen in number. A corresponding series of spines on the
lower border, termed chevron bones, equally long, were given off from
the junctions of the vertebrae on their under sides, and produced
downward. This vertical appendage is of some interest because its
expansion is like the tail of a fish. It suggests the possibility of
having been used in a similar way to the caudal fin as an organ for
locomotion in water, though it is possible that it may have also formed
an organ used in flight for steering in the air.
[Illustration: FIG. 28. EXTREMITY OF THE TAIL OF _RHAMPHORHYNCHUS
PHYLLURUS_ (MARSH)
Showing the processes on the upper and under sides of the vertebrae
which make the terminal leaf-like expansion]
The tail vertebrae from the Cambridge Greensand are mostly found isolated
or with not more than four joints in association. They are very like the
slender type of neck vertebrae seen in long-necked pterodactyles, but are
depressed, and though somewhat wider are not unlike the tail vertebrae of
the Rhamphorhynchus. The pneumatic foramen in them is a mere puncture.
They have no transverse processes or neural spines, nor indications of
ribs, or chevron bones.
The hindermost specimens of tail vertebrae observed have the neural arch
preserved to the end, as among reptiles; whereas in mammals this arch
becomes lost towards the end of the tail. The processes by which the
vertebrae are yoked together are small. There is nothing to suggest that
the tail was long, except the circumstance that the slender caudal
vertebrae are almost as long as the stout cervical vertebrae in the same
animal. No small caudal vertebrae have ever been found in the Cambridge
Greensand. The tail is very short, according to Professor Williston, in
the toothless Ornithostoma in the Chalk of Kansas.
CHAPTER X
THE HIP-GIRDLE AND HIND LIMB
The bones of the hip-girdle form a basin which incloses and protects the
abdominal vital organs. It consists on each side of a composite bone,
the unnamed bones--_ossa innominata_ of the older anatomists--which are
each attached to the sacrum on their inner side, and on the outer side
give attachment to the hind limbs. As a rule three bones enter into the
borders of this cup, termed the acetabulum, in which the head of the
thigh bone, named the Femur, moves with a more or less rotary motion.
There are a few exceptions in this division of the cup between three
bones, chiefly among Salamanders and certain Frogs. In Crocodiles the
bone below the acetabular cup is not divided into two parts. And in
certain Plesiosaurs from the Oxford Clay--Muraenosaurus--the actual
articulation appears to be made by two bones--the ilium and ischium. The
three bones which form each side of the pelvis are known as the ilium,
or hip bone, sometimes termed the aitch bone; secondly, the ischium, or
sitz bone, being the bone by which the body is supported in a sitting
position; and thirdly the pubis, which is the bone in front of the
acetabulum. The pubic bones meet in the middle line of the body on the
under side of the pelvis in man, and on each side are partly separated
from the ischia by a foramen, spoken of as the obturator foramen, which
in Pterodactyles is minute and almost invisible, when it exists.
There is often a fourth bony element in the pelvis. In some Salamanders
a single cartilage is directed forward, and forked in front. According
to Professor Huxley something of this kind is seen in the Dog. The pair
of bones which extend forward in front of the pelvis in Crocodiles may
be of the same kind, in which case they should be called prepubic bones.
But among the lower mammals named marsupials a pouch is developed for
the protection of the young and supported by two slender bones attached
to the pubes, and these bones have long been known as marsupial bones.
In a still lower group of mammalia named monotremata, which lay eggs,
and in many ways approximate to reptiles and birds, stronger bones are
developed on the front edge of the pubes, and termed prepubic bones.
They do not support a marsupium.
Naturalists have been uncertain as to the number of bones in the pelvis
of Pterodactyles, because the bones blend together early in life, as in
birds. Some follow the Amphibian nomenclature, and unite the ischium and
pubis into one bone, which is then termed ischium, when the prepubis is
termed the pubis, and regarded as removed from the acetabulum. There is
no ground for this interpretation, for the sutures are clear between the
three pelvic bones in the acetabulum in some specimens, like
_Cycnorhamphus Fraasii_, from Solenhofen, and some examples of
Ornithocheirus from the Cambridge Greensand. Pterodactyles all have
prepubic bones, which are only known in Ornithorhynchus and Echidna
among mammals, and are absent from the higher mammals and birds. They
are unknown in any other existing animals, unless present in Crocodiles,
in which ischium and pubis are always undivided. Therefore it is
interesting to examine the characters of the Ornithosaurian pelvis.
The acetabulum for the head of the femur is imperforate, being a simple
oval basin, as in Chelonian reptiles and the higher Mammals. It never
shows the mark of the ligamentous attachment to the head of the femur,
which is seen in Mammals. In Birds the acetabulum is perforated, as in
many of the fossils named Dinosaurs, and in Monotremata.
[Illustration: FIG. 29. COMPARISON OF THE LEFT SIDE OF THE PELVIS IN
A BIRD AND A PTERODACTYLE]
Secondly, the ilium is elongated, and extends quite as much in front of
the acetabulum as behind it. The bone is not very deep in this front
process. Among existing animals this relation of the bone is nearer to
birds than to any other type, since birds alone have the ilium extended
from the acetabulum in both directions. The form of the Pterodactyle
ilium is usually that of the embryo bird, and its slender processes
compare in relative length better with those of the unhatched fowl and
Apteryx of New Zealand than with the plate-like form in adult birds.
In mammals the ilium is directed forward, and even in the Cape ant-eater
Orycteropus there is only an inappreciable production of the bone
backward behind the acetabulum. Among reptiles the general position of
the acetabulum is at the forward termination of the ilium, though the
Crocodile has some extension of the bone in both directions, without
forming distinct anterior and posterior processes. This anterior and
posterior extension of the ilium is seen in the Theriodont reptiles of
Russia and of South Africa, as well as in Dinosaurs.
[Illustration: FIG. 30. LEFT PELVIC BONES WITH PREPUBIC BONE IN
_PTERODACTYLUS LONGIROSTRIS_]
Thirdly, in all pterodactyles the ischium and pubis are more or less
completely blended into a sheet of bone, unbroken by perforation, though
there is usually a minute vascular foramen; or the lower border may be
notched between the ischium and the pubis, as in some of the Solenhofen
species, and the pubis does not reach the median line of the body. But
in Dimorphodon the pelvic sheet of bone is unbroken by any notch or
perforation. The notch between the ischium and pubis is well marked in
_Pterodactylus longirostris_, and better marked in _Pterodactylus
dubius_, _Cycnorhamphus Fraasii_, and Rhamphorhynchus. The fossil
animals which appear to come nearest to the Pterodactyles in the
structure of the pelvis are Theriodonts from the Permian rocks of
Russia. The type known as Rhopalodon has the ilium less prolonged front
and back, and is much deeper than in any Pterodactyle; but the
acetabulum is imperforate, and the ischium and pubis are not always
completely separated from each other by suture. In the pelvis referred
to the Theriodont Deuterosaurus there is some approximation to the
pelvis of Rhamphorhynchus and of _Pterodactylus dubius_ in the depth of
the division between the pubis and ischium.
[Illustration: FIG. 31 PELVIS AND PREPUBIC BONES OF RHAMPHORHYNCHUS
On the left-hand side the two prepubic bones are separate. On the
right-hand they are united into a transverse bar which overlaps the
front of pelvis seen from the under side]
There are three modifications of the Ornithosaurian pelvis. First, the
type of Rhamphorhynchus, in which the pubis and ischium are inclined
somewhat backward, and in which the two prepubic bones are triangular,
and are often united together to form a transverse bow in front of the
pubic region.
Secondly, there is the ordinary form of pelvis in which the pubis and
ischium usually unite with each other down their length, as in
Dimorphodon, but sometimes, as in _Pterodactylus dubius_, divide
immediately below the acetabulum. All these types possess the
paddle-shaped prepubic bones, which are never united in the median line.
Thirdly, there is the cretaceous form indicated by Ornithocheirus and
Ornithostoma, in which the posterior half of the ilium is modified in a
singular way, since it is more elevated towards the sacrum than the
anterior half, suggesting the contour of the upper border of the ilium
in a lizard. Without being reptilian--the anterior prolongation of the
bone makes that impossible--it suggests the lizards. This type also
possesses prepubic bones. They appear, according to Professor Williston,
to be more like the paddle-shaped bones of Pterodactylus than like the
angular bones in Rhamphorhynchus. The prepubic bones are united in the
median line as in Rhamphorhynchus. But their median union in that genus
favours the conclusion that the bones were united in the median line in
all species, though they are only co-ossified in these two families.
[Illustration: FIG. 32. THE PELVIC BONES OF AN ALLIGATOR SEEN FROM
BELOW
The bones in front are here regarded as prepubic, but are commonly
named pubic]
This median union of the prepubic bones is a difference from those
mammals like the Ornithorhynchus and Echidna, which approach nearest to
the Reptilia. In them the prepubic bones have a long attachment to the
front margin of the pubis, and extend their points forward without any
tendency for the anterior extremities to approximate or unite. The
marsupial mammals have the same character, keeping the marsupial bones
completely distinct from each other at their free extremities. The only
existing animals in which an approximation is found to the prepubic
bones in Pterodactyles are Crocodiles, in bones which most writers term
the pubic bones. This resemblance, without showing any strong affinity
with the Crocodilia, indicates that Crocodiles have more in common with
the fossil flying animals than any other group of existing reptiles; for
other reptiles all want prepubic bones, or bones in front of the pubic
region.
THE HIND LIMB
The hind limb is exceptionally long in proportion to the back. This is
conspicuous in the skeletons of the short-tailed Pterodactyles, and is
also seen in Dimorphodon. In Rhamphorhynchus the hind limb is relatively
much shorter, so that the animal, when on all fours, may have had an
appearance not unlike a Bat in similar position. The limb is
exceptionally short in the little _Ptenodracon brevirostris_. The bones
of the hind limb are exceptionally interesting. One remarkable feature
common to all the specimens is the great elongation of the shin bones
relatively to the thigh bones. The femur is sometimes little more than
half the length of the tibia, and always shorter than that bone. The
proportions are those of mammals and birds. Some mammals have the leg
shorter than the thigh, but mammals and birds alone, among existing
animals, have the proportions which characterise Pterodactyles. The
foot appears to have been applied to the ground not always as in a bird,
but more often in the manner of reptiles, or mammals in which the digits
terminate in claws.
THE FEMUR
[Illustration: FIG. 33. THE FEMUR
On the right is a front view of femur of a bear. In the middle are
front and side views of the femur of Ornithocheirus. On the left is
the femur of Echidna. These comparisons illustrate the mammalian
characters of the Pterodactyle thigh bone]
The thigh bone, on account of the small size of many of the specimens,
is not always quite clear evidence as an indication of technical
resemblance to other animals. The bone is always a little curved, has
always a rounded, articular head, and rounded distal condyles. Its most
remarkable features are shown in the large, well-preserved specimens
from the Cambridge Greensand. The rounded, articular head is associated
with a constricted neck to the bone, followed by a comparatively
straight shaft with distal condyles, less thickened than in mammals. No
bird is known, much less any reptile, with a femur like Ornithocheirus.
Only among Mammals is a similar bone known with a distinct neck; and
only a few mammals have the exceptional characters of the rounded head
and constricted neck at all similar to the Cretaceous Pterodactyles. A
few types, such as the higher apes, the Hyrax, and animals especially
active in the hind limb, have a femur at all resembling the Pterodactyle
in the pit for the obturator externus muscle, behind the trochanter
major, such as is seen in a small femur from Ashwell. The femur varies
in different genera, so as to suggest a number of mammalia rather than
any particular animal for comparison. These approximations may be
consequences of the ways in which the bones are used. When functional
modifications of the skeleton are developed, so as to produce similar
forms of bones, the muscles to which they give attachment, which act
upon the bones, and determine their growth, are substantially the same.
In the _Pterodactylus longirostris_ the femur corresponds in length to
about eleven dorsal vertebrae. The end next the shin bone is less
expanded than is usual among Mammals, and rather suggests an approach to
the condition in Crocodiles, in the moderate thickness and breadth of
the articular end, and the slight development of the terminal
pulley-joint. One striking feature of the femur is the circumstance that
the articular head, as compared with the distal end, is directed forward
and very slightly inward and upward. So that allowing for the outward
divergence of the pelvic bones, as they extend forward, there must have
been a tendency to a knock-kneed approximation of the lower ends of the
thigh bones, as in Mammals and Birds, rather than the outward divergence
seen in Reptiles.
Apparently the swing of the leg and foot, as it hung on the distal end
of the femur, must have tended rather to an inward than to an outward
direction, so that the feet might be put down upon the same straight
line; this arrangement suggests rapid movement.
[Illustration: FIG. 34. COMPARISON OF THE TIBIA AND FIBULA IN
ORNITHOSAUR AND VULTURE]
TIBIA AND FIBULA
In _Pterodactylus longirostris_ the tibia is slender, more than a fifth
longer than the femur. A crest is never developed at the proximal end,
like that seen in the Guillemot and Diver and other water birds. The
bone is of comparatively uniform thickness down the shaft in most of the
Solenhofen specimens, as in most birds. At the distal end the shin bone
commonly has a rounded, articular termination, like that seen in birds.
This is conspicuous in the _Pterodactylus grandis_. In other specimens
the tarsal bones, which form this pulley, remain distinct from the
tibia; and the upper row of these bones appears to consist of two
bones, like those which in many Dinosaurs combine to form the
pulley-like end of the tibia which represents the bird's drum-stick
bone. They correspond with the ankle bones in man named astragalus and
os calcis.
Complete English specimens of tibia and fibula are found in the genus
Dimorphodon from the Lias, in which the terminal pulley of the distal
end has some expansion, and is placed forward towards the front of the
tibia, as in some birds. The rounded surface of the pulley is rather
better marked than in birds. The proximal end of the shaft is relatively
stout, and is modified by the well-developed fibula, which is a short
external splint bone limited to the upper half of the tibia, as in
birds; but contributing with it to form the articular surface for the
support of the lower end of the femur, taking a larger share in that
work than in birds. Frequently there is no trace of the fibula visible
in Solenhofen specimens as preserved; or it is extremely slender and
bird-like, as in _Pterodactylus longirostris_. In Rhamphorhynchus it
appears to extend the entire length of the tibia, as in Dinosaurs. In
the specimens from the Cambridge Greensand there is indication of a
small proximal crest to the tibia with a slight ridge, but no evidence
that this is due to a separate ossification. The patella, or knee-cap,
is not recognised in any fossil of the group. There is no indication of
a fibula in the specimens thus far known from the Chalk rocks either of
Kansas in America, or in England.
The region of the tarsus varies from the circumstance that in many
specimens the tibia terminates downward in a rounded pulley, like the
drum-stick of a bird; while in other specimens this union of the
proximal row of the tarsal bones with the tibia does not take place, and
then there are two rows of separate tarsal bones, usually with two bones
in each row. When the upper row is united with the tibia the lower row
remains distinct from the metatarsus, though no one has examined these
separate tarsal bones so as to define them.
THE FOOT
[Illustration: FIG. 35. METATARSUS AND DIGITS IN THREE TYPES OF
ORNITHOSAURS]
The foot sometimes has four toes, and sometimes five. There are four
somewhat elongated, slender metatarsal bones, which are separate from
each other and never blended together, as in birds. There has been a
suspicion that the metatarsal bones were separate in the young
Archaeopteryx. In the young of many birds the row of tarsal bones at the
proximal end of the metatarsus comes away, and there is a partial
division between the metatarsal bones, though they remain united in the
middle. And among Penguins, in which the foot bones are applied to the
ground instead of being carried in the erect position of ordinary birds,
there is always a partial separation between the metatarsal bones,
though they become blended together. The Pterodactyle is therefore
different from birds in preserving the bones distinct through life, and
this character is more like Reptiles than Mammals. The individual bones
are not like those of Dinosaurs, and diverge in Rhamphorhynchus as
though the animals were web-footed. There is commonly a rudimentary
fifth metatarsal. It is sometimes only a claw-shaped appendage, like
that seen in the Crocodile. It is sometimes a short bone, completely
formed, and carrying two phalanges in Solenhofen specimens: though no
trace of these phalanges is seen in the large toothless Pterodactyles
from the Cretaceous rocks of North America. In the _Pterodactylus
longirostris_ the number of foot bones on the ordinary digits is two,
three, four, five, as in lizards; but the short fifth metatarsal has
only two toe bones. In Dimorphodon the fifth digit was bent upward, and
supported a membrane for flight. There are slight variations in the
number of foot bones. In the species _Pterodactylus scolopaciceps_ the
number of bones in the toes follows the formula two, three, three, four.
In _Pterodactylus micronyx_ the number is two, three, three, three. The
terminal claws are much less developed than is usual with Birds; and
there is a difference from Bats in the unequal length of the digits.
Taken as a whole, the foot is perhaps more reptilian than avian, and in
some genera is crocodilian.
The foot is the light foot of an active animal. Von Meyer thought that
the hind legs were too slender to enable the animal to walk on land; and
Professor Williston, of the University of Kansas, remarks that the
rudimentary claws and weak toes indicate that the animal could not have
used the feet effectively for grasping, while the exceedingly free
movement of the femur indicates great freedom of movement of the hind
legs; and he concludes that the function of the legs was chiefly for
guidance in flight through their control over the movements, and
expresses his belief that the animal could not have stood upon the
ground with its feet. There may be evidence to sustain other views. If
the limb bones are reconstructed, they form limbs not wanting in
elegance or length. If it is true, as Professor Williston suggests, that
the weight of his largest animals with the head three feet long, and a
stretch of wing of eighteen or nineteen feet, did not exceed twenty
pounds, there can be no objection to regarding these animals as
quadrupeds, or even as bipeds, on the ground of the limbs lacking the
strength necessary to support the body. The slender toes of many birds,
and even the two toes of the ostrich, may be thought to give less
adequate support for those animals than the metatarsals and digits of
Pterodactyles.
CHAPTER XI
SHOULDER-GIRDLE AND FORE LIMB
STERNUM
The sternum is always a distinguishing part of the bony structure of the
breast. In Crocodiles it is a cartilage to which the sternal ribs unite;
and upon its front portion a flat knife-like bone called the
interclavicle is placed. In lizards like the Chameleon, it is a
lozenge-shaped structure of thin bony texture, also bearing a long
interclavicle, which supports the clavicular bones, named collar bones
in man, which extend outward to the shoulder blades. Among mammals the
sternum is usually narrow and flat, and often consists of many
successive pieces in the middle line, on the under side of the body.
Among Bats the anterior part is somewhat widened from side to side, to
give attachment to the collar bones, but the sternum still remains a
narrow bone, much narrower than in Dolphins, and not differing in
character from many other Mammals, notwithstanding the Bat's power of
flight. The bone develops a median keel for the attachment of the
muscles of the breast, but something similar is seen in burrowing
Insectivorous mammals like the Moles. So that, as Von Meyer remarked,
the presence of a keel on the sternum is not in itself sufficient
evidence to prove flight.
Among birds the sternum is greatly developed. Broad and short in the
Ostrich tribe, it is devoid of a keel; and therefore the keel, if
present in a bird, is suggestive of flight. The keel is differently
developed according to the mode of attachment of the several pectoral
muscles which cover a bird's breast. In several water birds the keel is
strongly developed in front, and dies away towards the hinder part of
the sternum, as in the Cormorant and its allies. The sternum in German
Pterodactyles is most nearly comparable to these birds.
[Illustration: FIG. 36. COMPARISON OF THE STERNUM]
In the Solenhofen Slate the sternum is fairly well preserved in many
Ornithosaurs. It is relatively shorter than in birds, and is broader
than long; but not very like the sternum of reptile or mammal in form.
The keel is limited to the anterior part of the shield of the sternum,
as in Merganser and the Cormorant, and is prolonged forward for some
distance in advance of it. Von Meyer noticed the resemblance of this
anterior process to the interclavicle of the Crocodile in position; but
it is more like the keel of a bird's sternum, and is not a separate bone
as in Reptiles. In Pterodactyles from the Cretaceous rocks, the side
bones, called coracoids, are articulated to saddle-shaped surfaces at
the hinder part of the base of this keel, which are parallel in
Ornithocheirus, as in most birds, but overlap in Ornithodesmus, as in
Herons and wading birds.
[Illustration: FIG. 37. STERNUM IN ORNITHOCHEIRUS FROM THE CAMBRIDGE
GREENSAND
Showing the strong keel and the facets for the coracoid bones on its
hinder border above the lateral constrictions]
The keel was pneumatic, and when broken is seen to be hollow, and
appears to have been exceptionally high in Rhamphorhynchus, a genus in
which the wing bones are greatly elongated. Von Meyer found in
Rhamphorhynchus on each side of the sternum a separate lateral plate
with six pairs of sternal ribs, which unite the sternum with the dorsal
ribs, as in the young of some birds. The hinder surface of the sternum
is imperfectly preserved in the toothless Pterodactyles of Kansas.
Professor Williston states that the bone is extremely thin and
pentagonal in outline, projecting in front of the coracoids, in a stout,
blunt, keel-like process, similar to that seen in the Pterodactyles of
the Cambridge Greensand. American specimens have not the same notch
behind the articulation for the coracoid to separate it from the
transverse lateral expansion of the sternal shield. The lateral margin
in the Cambridge Greensand specimens figured by Professor Owen and
myself is broken; but Professor Williston had the good fortune to find
on the margin of the sternum the articular surfaces which gave
attachment to the sternal ribs. The margin of the sternal bone thickens
at these facets, four of which are preserved. The sternum in
Ornithostoma was about four and a half inches long by less than five and
a half inches wide. The median keel extends forward for rather less than
two inches, while in the smaller Cambridge species of Ornithocheirus it
extends forward for less than an inch and a half.
A sternum of this kind is unlike that of any other animal, but has most
in common with a bird; and may be regarded as indicating considerable
power of flight. The bone cannot be entirely attributed to the effect of
flight, since there is no such expanded sternal shield in Bats. The
small number of sternal ribs is even more characteristic of birds than
mammals or reptiles.
THE SHOULDER-GIRDLE
The bones which support the fore limb are one of the distinctive regions
of the skeleton defining the animal's place in nature. Among most of the
lower vertebrata, such as Amphibians and Reptiles, the girdle is a
double arch--the arch of the collar bone or clavicles in front, and the
arch of the shoulder-blade or scapula behind. The clavicular arch, when
it exists, is formed of three or five parts--a medium bar named the
interclavicle, external to which is a pair of bones called clavicles,
reaching to the front of the scapulae when they are present; and
occasionally there is a second pair of bones called supraclavicles,
extending from the clavicles up the front margins of the scapulae. Thus
the clavicular arch is placed in front of the scapular arch. The
supraclavicles are absent from all living Reptiles, and the clavicles
are absent from Crocodiles. The interclavicle is absent from all mammals
except Echidna and Ornithorhynchus. Clavicles also may be absent in some
orders of mammals. Hence the clavicular arch may be lost, though the
collar bones are retained in man.
The scapular arch also is more complicated and more important in the
lower than in the higher vertebrata. It may include three bones on each
side named coracoid, precoracoid, and scapula. But in most vertebrates
the coracoid and precoracoid appear never to have been segmented so as
to be separated from each other; and it is only among extinct types of
reptiles, which appear to approximate to the Monotreme mammals, that
separate precoracoid bones are found; though among most mammals,
probably, there are stages of early development in which precoracoids
are represented by small cartilages, though few mammals except Edentata
like the Sloths and Ant-eaters, retain even the coracoids as distinct
bones. Therefore, excepting the Edentata and the Monotremes, the
distinctive feature of the mammalian shoulder-girdle appears to be that
the limbs are supported by the shoulder-blades, termed the scapulae.
Among reptiles there are several distinct types of shoulder-girdle.
Chelonians possess a pair of bones termed coracoids which have no
connexion with a sternum; and their scapulae are formed of two widely
divergent bars, divided by a deeper notch than is found in any fossil
reptiles. Among Lizards both scapula and coracoid are widely expanded,
and the coracoid is always attached to the sternum. Chameleons have the
blade of the scapula long and slender, but the coracoid is always as
broad as it is long. Crocodiles have the bone more elongated, so that it
has somewhat the aspect of a very strong first sternal rib when seen on
the ventral face of the animal. The bone is perforated by a foramen,
which would probably lie in the line of separation from the precoracoid
if any such separation had ever taken place. The scapula, or
shoulder-blade, of Crocodiles is a similar flat bone, very much shorter
than the scapula of a Chameleon, and more like that of the New Zealand
Hatteria. Thus there is very little in common between the several
reptilian types of shoulder-girdle.
[Illustration: FIG. 38. COMPARISON OF SCAPULA AND CORACOID IN THREE
PTERODACTYLES AND A BIRD]
In birds the apparatus for the support of the wings has a far-off
resemblance to the Crocodilian type. The coracoid bones, instead of
being directed laterally outward and upward from the sternum, as among
Crocodiles, are directed forward, so as to prolong the line of the
breast bone, named the sternum. The bird's coracoid is sometimes
flattened towards the breast bone among Swans and other birds; yet as a
rule the coracoid is a slender bar, which combines with the still more
slender and delicate blade of the scapula, which rests on the ribs, to
make the articulation for the upper arm bone. Among reptiles the scapula
and coracoid are more or less in the same straight line, as in the
Ostrich, but in birds of flight they meet at an angle which is less than
a right angle, and where they come in contact the external surface is
thickened and excavated to make the articulation for the head of the
humerus. There is nothing like this shoulder-girdle outside the class of
birds, until it is compared with the corresponding structure in these
extinct animals called Pterodactyles. The resemblance between the two is
surprising. It is not merely the identity of form in the coracoid bone
and the scapula, but the similar angle at which they meet and the
similar position of the articulation for the humerus. Everything in the
Pterodactyle's shoulder-girdle is bird-like, except the absence of the
representative of the clavicles, that forked #V#-shaped bone of the bird
which in scientific language is known as the furculum, and is popularly
termed the "merry-thought." This kind of shoulder-girdle is found in the
genera from the Lias and the Oolitic rocks, both of this country and
Germany.
In the Cretaceous rocks the scapula presents, in most cases, a different
appearance. The coracoid is an elongated, somewhat triangular bone,
compressed on the outer margin as in birds, but differing alike from
birds and other Pterodactyles in not being prolonged forward beyond the
articulation for the humerus. In these Cretaceous genera, toothed and
toothless alike, the articulation for the upper arm bone truncates the
extremity of the coracoid, so that the bone is less like that of a bird
in this feature. Perhaps it shows a modification towards the crocodilian
direction. The scapula, which unites with the coracoid at about a right
angle, is similarly truncated by the articular surface for the humerus;
but the bone is somewhat expanded immediately beyond the articulation,
and compressed; and instead of being directed backward, it is directed
inward over the ribs to articulate with the neural arches of the early
dorsal vertebrae in the genera found in strata associated with the Chalk.
As the bone approaches this articulation, it thickens and widens a
little, becoming suddenly truncated by an ovate facet, which exactly
corresponds to the transversely ovate impression, concave from front to
back, which is seen in the neural arches of the dorsal vertebrae on which
it fits. This condition is not present in all Cretaceous Pterodactyles.
It does not occur in the Kansas fossil, named by Professor Marsh,
Nyctodactylus. And it appears to be absent from the Pterodactyles of the
English Weald, named Ornithodesmus.
[Illustration: FIG. 39. THE NOTARIUM
An ossification which gives attachment to the scapulae seen in the
early dorsal vertebra of Ornithocheirus
(From the Cambridge Greensand)]
[Illustration: FIG. 40. RESTORATION OF THE SHOULDER-GIRDLE IN THE
CRETACEOUS ORNITHOCHEIRUS
Showing how the scapulae articulate with a vertebra and the
articulation of the coracoids with the sternum. The humeral
articulation with the coracoid is unlike the condition shown
in other Ornithosaurs]
There is no approach to this transverse position of the scapulae among
birds. And while the form of the bones in the older genera of
Ornithosaurs is singularly bird-like, the angular arrangement in this
Cretaceous genus is obtained by closely approximating the articulations
on the sternum, so that the coracoids extend outward as in reptiles,
instead of forward as in birds; and the extremities of the scapulae
similarly approximate towards each other. This rather recalls the
relative positions of scapula and coracoid among crocodiles. If
crocodile and bird had been primitive types of animals instead of
surviving types, it might almost seem as though there had been a cunning
and harmonious blending of one with the other in evolving this form of
shoulder-girdle.
THE FORE LIMB
The bones of the fore limb, generally, correspond in length with the
similar parts of the hind limb. The upper arm bone corresponds with the
upper leg bone, and the fore-arm bone is as long as the fore-leg bone;
then differences begin. The bones which correspond to the back of the
hand in man, termed the metacarpus, are variable in length in
Pterodactyles--sometimes very long and sometimes short. The wing
metacarpal bone is always stout, and the others are slender. The
extremity of the metacarpus was applied to the ground. Three small
digits of the hand are developed from the three small metacarpal bones,
and terminate in large claws.
The great wing finger was bent backward, and only touched the ground
where it fitted upon the wing metacarpal bone. It appears sometimes to
have been as long as the entire vertebral column.
Owing to the circumstance that the joint in the arm in Pterodactyles was
not at the wrist as among birds, but between the metacarpus and the
phalanges, it follows that the fore limb was longer than the hind limb
when the metacarpus was long; but the difference would not interfere
with the movements of the animal, either upon four feet or on two feet,
for in bats and birds the disproportion in length is greater.
HUMERUS OR UPPER ARM BONE
The first bone in the fore-arm, the humerus, is remarkable chiefly for
the compressed crescent form of its upper articular end, which is never
rounded like the head of the upper arm bone in man, and secondly for the
great development of the external process of bone near that end, termed
the radial crest. Sir Richard Owen compared the bone to the humerus of
both birds and crocodiles, but in its upper articular end the crocodile
bone may be said to be more like a bird than it is like the
Pterodactyle. In flying reptiles the articular surface next to the
shoulder-girdle is somewhat saddle-shaped, being concave from side to
side above and convex vertically, while most animals with which it can
be compared have the articular head of the bone convex in both
directions. A remarkable exception to this general rule is found in some
fossil animals from South Africa, which, from resemblance to mammals in
their teeth, have been termed Theriodonts. They sometimes have the head
of the bone concave from side to side and convex in the vertical
direction. To this condition Ornithorhynchus makes a slight
approximation. The singular expansion of the structure called the radial
crest finds no close parallel in reptiles, though Crocodiles have a
moderate crest on the humerus in the same position; and in Theriodonts
the radial crest extends much further down the shaft of the humerus. No
bird has a radial crest of a similar kind, though it is prolonged some
way down the shaft in Archaeopteryx. In Pterodactyles it sometimes
terminates outward in a smooth, rounded surface, which might have been
articular if any structure could have articulated with it. There is also
a moderate expansion of the bone on the ulnar side in some
Pterodactyles, so that the proximal end often incloses nearly
three-fourths of an ovate outline. The termination of the radial crest
is at the opposite end of this oval to the wider articular part of the
head of the bone, in some specimens from the Cambridge Greensand. The
radial crest is more extended in Rhamphorhynchus. All specimens of the
humerus show a twist in the length of the bone, so that the end towards
the fore-arm, which is wider than the shaft, makes a right angle with
the radial crest on the proximal end, which is not seen in birds. The
shaft of the humerus is always stouter than that of the femur, though
different genera differ in this respect.
The humerus in genera from rocks associated with the Chalk presents two
modifications, chiefly seen in the characters of the distal end of the
bone. One of these is a stout bone with a curiously truncated end where
it joins the two bones of the fore-arm; and the other is more or less
remarkable for the rounded form of the distal condyles. Both types show
distinct articular surfaces. The inner one is somewhat oblique and
concave, the outer one rounded; the two being separated by a concave
channel, so that the ulna makes an oblique articulation with the bone as
in birds, and the radius articulates by a more or less truncated or
concave surface.
[Illustration: FIG. 41. COMPARISON OF THE HUMERUS IN PTERODACTYLE AND
BIRD]
ULNA AND RADIUS
[Illustration: FIG. 42. COMPARISON OF THE BONES OF THE FORE-ARM IN
BIRD AND ORNITHOSAUR]
The bones of the fore-arm are similar to each other in size, and if
there be any difference between them the ulna is slightly the larger.
There is some evidence that in Rhamphorhynchus the upper end of the ulna
was placed behind the radius, probably in consequence of the mode of
attachment of those bones to the humerus. The ulna abutted towards the
inner and lower border, while the radius was towards the upper border,
consequent upon the twist in the humerus. This condition corresponds
substantially with the arrangement in birds, but differs from birds in
the relatively more important part taken by the radius in making the
articulation. The bones are compared in Dimorphodon with the Golden
Eagle drawn of the same size (Fig. 42). In birds the ulna supports the
great feathers of the wing, and this may account for the size of the
bone. The ulna is best seen at its proximal end in the specimens from
the Cambridge Greensand, where there is a terminal olecranon
ossification forming an oblique articulation, which frequently comes
away and is lost. It is sometimes well preserved, and indicated by a
suture. The examples of ulna from the Lias show a slight expansion of
the bone at both ends, and at the distal end toward the wrist the
articulation is well defined, where the bone joins the carpus. The
larger specimens of the bone are broken. The distal articular surface is
only connected with the proximal end of the bone in small specimens: it
always shows on the one margin a concavity, followed by a prominent
boss, and an oblique articulation beyond the boss. On the side towards
the radius, on the lower end of the shaft there is an angular ridge,
which marks the line along which the ulna overlaps the radius. The
lower end of the radius has a simple, slightly convex articulation,
somewhat bean-shaped. No rotation of these bones on each other was
possible as in man. There is a third bone in the fore-arm. This bone,
named the pteroid, is commonly seen in skeletons from Solenhofen. It was
regarded by Von Meyer as having supported the wing membrane in flight.
Some writers have interpreted it as an essential part of the
Pterodactyle skeleton, and Von Meyer thought that it might possibly
indicate a fifth digit in the hand. The only existing structure at all
like it is seen in the South African insectivorous mammal named
_Chrysochloris capensis_, the golden mole, which also has three bones in
the fore-arm, the third bone extending half-way up towards the humerus.
In that animal the third bone appears to be behind the others and
adjacent to the ulna. In the German fossils the pteroid articulated with
a separate carpal or metacarpal bone, placed on the side of the arm
adjacent to the radius, and the radius is always more inward than the
ulna. If the view suggested by Von Meyer is adopted, this bone would be
a first digit extending outward and backward towards the humerus. That
view was adopted by Professor Marsh. It involves the interpretation of
what has been termed the lateral carpal as the first metacarpal bone,
which would be as short as that of a bird, but turned in the opposite
direction backward. The first digit would then only carry one phalange,
and would not terminate in a claw, but lie in the line of the tendon
which supports the anterior wing membrane of a bird.
The third bone in the fore-arm of Chrysochloris does not appear to
correspond to a digit. The bone is on the opposite side of the arm to
the similar bone of a Pterodactyle, and therefore cannot be the same
structure in the Golden Mole. The interpretation which makes the pteroid
bone the first digit has the merit of accounting for the fifth digit of
the hand. All the structures of the hand are consistent with this view.
The circumstance that the bone is rarely found in contact with the
radius, but diverging from it, shows that it plays the same part in
stretching the membrane in advance of the arm, that the fifth digit
holds in supporting the larger wing membrane behind the arm.
According to Professor Williston, the American toothless Pterodactyle
Ornithostoma has but a single phalange on the corresponding first toe of
the hind foot, and that bone he describes as long, cylindrical, gently
curved, and bluntly pointed. There is some support for this
interpretation; but I have not seen any English or German Pterodactyles
with only one phalange in the first toe.
The wing in Pterodactyles would thus be stretched between two fingers
which are bent backward, the three intermediate digits terminating in
claws.
THE CARPUS
The wrist bones in the reptilia usually consist of two rows. In
Crocodiles, in the upper row there is a large inner and a small outer
bone, behind which is a lunate bone, the remainder of the carpus being
cartilaginous. Only one carpal is converted into bone in the lower row.
It is placed immediately under the smaller upper carpal. In Chelonians,
the turtle and tortoise group, the characters of the carpus vary with
the family. In the upper row there are usually two short carpals, which
may be blended, under the ulna; while the two under the radius are
commonly united. The lower row is made up of several small bones.
Lizards, too, usually have three bones in the proximal row and five
smaller bones in the distal row.
The correspondence of the distal carpals with the several metacarpal
bones of the middle hand is a well-known feature of the structure of the
wrist.
Von Meyer remarks that the carpus is made up of two rows of small bones
in the Solenhofen Pterodactyles; while in birds there is one row
consisting of two bones. The structure of the carpus is not distinct in
all German specimens; but in the short-tailed Solenhofen genera the
bones in the two rows retain their individuality.
In all the Cretaceous genera the carpal bones of each row are blended
into a single bone, so that two bones are superimposed, which may be
termed the proximal and distal carpals. One specimen shows by an
indication of sutures the original division of the distal carpal into
three bones; and the separated constituent bones are very rarely met
with. Two bones of the three confluent elements contribute to the
support of the wing metacarpal, and the third gives an articular
attachment to the bone which extends laterally at the inner side of the
carpus, which I now think may be the first metacarpal bone turned
backward towards the humerus. The three component bones meet in the
circular pneumatic foramen in the middle of the under side of the distal
carpal. There is no indication of division of the proximal carpal in
these genera into constituent bones.
[Illustration: FIG. 43. CARPUS FROM ORNITHOCHEIRUS
(Cambridge Greensand)]
This condition is somewhat different from birds. In 1873 Dr. Rosenberg,
of Dorpat, showed that there is in the bird a proximal carpal formed of
two elements, and a distal carpal also formed of two elements. Therefore
the two constituents of the distal carpal in the bird which blends in
the mature animal with the metacarpus, forming the rounded pulley joint,
may correspond with two of the three bones in the Cretaceous
Pterodactyle _Ornithocheirus._
The width of a proximal carpal rarely exceeds two inches, and that of a
distal carpal is about an inch and three-quarters. Two such bones when
in contact would not measure more than one inch in depth. The lower
surface shows that the wing had some rotary movement upon the carpus
outward and backward.
METACARPUS
[Illustration: FIG. 44. METACARPUS IN TWO ORNITHOSAURS]
The metacarpus consists of bones which correspond to the back of the
hand. The first digit of the hand in clawed animals has the metacarpal
bone short, or shorter than the others. Among mammals metacarpal bones
are sometimes greatly elongated; and a similar condition is found in
Pterodactyles, in which the metacarpal bone may be much longer than the
phalange which is attached to it. Two metacarpal bones appear to be
singularly stouter than the others. The first bone of the first digit,
if rightly determined, is much shorter than the others, and is, in fact,
no longer than the carpus (Fig. 43). It is a flat oblong bone, attached
to the inner side of the lower carpal, and instead of being prolonged
distally in the same direction as the other metacarpal bones, is turned
round and directed upward, so that its upper edge is flush with the base
of the radius, and gives attachment to a bone which resembles a terminal
phalange of the wing finger. According to this interpretation it is the
first and only phalange in the first digit. The bone is often about half
as long as the fore-arm, terminates upward in a point, is sometimes
curved, and frequently diverges outward from the bones of the fore-arm,
as preserved in the associated skeleton, being stretched towards the
radial crest of the humerus. This mode of attachment of the supposed
first metacarpal, which is true for all Cretaceous pterodactyles, has
not been shown to be the same for all those from the Solenhofen Slate.
There is no greater anomaly in this metacarpal and phalange on the
inner side being bent backward, than there is in the wing finger being
bent backward on the outer side. The three slender intervening digits
extend forward between them, as though they were applied to the ground
for walking.
The bone which is usually known as the wing metacarpal is frequently
stouter at the proximal end towards the carpus than towards the
phalange. At the carpal end it is oblong and truncated, with a short
middle process, which may have extended into the pit in the base of the
carpal bone; while the distal terminal end is rounded exactly like a
pulley. There is great difference in the length of the metacarpus. In
the American genus Ornithostoma it is much longer than the fore-arm. In
Rhamphorhynchus it is remarkably short, though perhaps scarcely so short
as in Dimorphodon or in Scaphognathus. The largest Cretaceous examples
are about two inches wide where they join the carpus. The bone is
sometimes a little curved.
Between the first and fifth or wing metacarpal are the three slender
metacarpal bones which give attachment to the clawed digits. They bear
much the same relation to the wing metacarpal that the large metatarsal
of a Kangaroo has to the slender bones of the instep which are parallel
to it.
The facet for the wing metacarpal on the carpus is clearly recognised,
but as a rule there is no surface with which the small metacarpals can
be separately articulated. One or two exceptional specimens from the
Cambridge Greensand appear to have not only surfaces for the wing
metacarpal, but two much smaller articular surfaces, giving attachment
to smaller metacarpals; while in one case there appears to be only one
of these additional impressions. It is certain that all the animals from
the Lias and Oolites have three clawed digits, but at present I have
seen no evidence that there were three in the Cretaceous genera, though
Professor Williston's statements and restoration appear to show that the
toothless Pterodactyles have three. Another difference from the Oolitic
types, according to Professor Williston, is in the length of the slender
metacarpals of the clawed phalanges being about one-third that of the
wing metacarpal, but this is probably due to imperfect ossification at
the proximal end; for at the distal end the bones all terminated on the
same level, showing that the four outer digits were applied to the
ground to support the weight of the body. The corresponding bone in the
Horse and Oxen is carried erect, so as to be in a vertical line with the
bones of the fore-arm; and the same position prevails usually, though
not invariably, with the corresponding bone in the hind limb, while in
many clawed mammals the metacarpus and metatarsus are both applied upon
the ground. In Pterodactyles the metatarsal bones are preserved in the
rock in the same straight line with the smaller bones of the foot, or
make an angle with the shin bone, leading to the conviction that the
bones of the foot were applied to the ground as in Man, and sometimes as
in the Dog, and were thus modified for leaping. Just as the human
metacarpus is extended in the same line with the bones of the fore-arm,
and the movement of jointing occurs where the fingers join the
metacarpus, so Pterodactyles also had these bones differently modified
in the fore and hind limbs for the functions of life. The result is to
lengthen the fore limb as compared with the hind limb by introducing
into it an elevation above the ground which corresponds to the length of
the metacarpus, always supposing that the animal commonly assumed the
position of a quadruped when upon the earth's surface.
This position of the metacarpus is a remarkable difference from Birds,
because when the bird's wing is at rest it is folded into three
portions. The upper arm bone extends backward, the bones of the fore-arm
are bent upon it so as to extend forward, and then at the wrist the
third portion, which includes the metacarpus and finger bones, is bent
backward. So that the metacarpus in the Pterodactyle differs from birds
in being in the same line as the bones of the fore-arm, whereas in birds
it is in the same line with the digit bones of the hand. It is worthy of
remark that in Bats, which are so suggestive of Pterodactyles in some
features of the hand, the metacarpals and phalanges are in the same
straight line; so that in this respect the bat is more like the bird.
But Pterodactyles in the relation of these bones to flight are quite
unlike any other animal, and have nothing in common with the existing
animals named Reptiles.
THE HAND
From what has just been said it follows that the construction of the
hand is unique. It may be contrasted with the foot of a bird. The bone
which is called, in the language of anatomists, the tarso-metatarsus,
and is usually free from feathers and covered with skin, is commonly
carried erect in birds, so that the whole body is supported upon it; and
from it the toes diverge outward. It is formed in birds of three
separate bones blended together. In the fore limb of the Pterodactyle
the metacarpus has the same relation to the bones of the fore-arm that
the metatarsus has to the corresponding bones of the leg in a bird. But
the three metacarpal bones in the Pterodactyle remain distinct from each
other, perhaps because the main work of that region of the skeleton has
devolved upon the digit called the wing finger, which is not recognised
in the bird. In the Pterodactyles from the Solenhofen Slate there is a
progressive number of phalanges in the three small digits of the hand,
which were applied to the ground. This number in the great majority of
species follows the formula of two bones in the first, three bones in
second, and four in the third; so that in the innermost of the clawed
digits only one bone intervenes between the metacarpal and the claw. The
fingers slightly increase in length with increase in number of bones
which form them.
[Illustration: FIG. 45. CLAW PHALANGE FROM THE HAND IN
ORNITHOCHEIRUS. (Half natural size)]
[Illustration: FIG. 46. METACARPUS AND DIGITS OF THE HAND IN BIRDS
WITH CLAWS]
The terminal claw bones are unlike the claws of Birds or Reptiles. They
are compressed from side to side, and extremely deep and strong, with
evidence of powerful attachment for ligaments, so that they rather
resemble in their form and large size the claws of some of the
carnivorous fossil reptiles, often grouped as Dinosauria, such as have
been termed Aristosuchus and Megalosaurus. In the hand of the Ostrich
the first and second digits terminate in claws, while the third is
without a claw. But these claws of the Ostrich and other birds are
slender, curved, and rather feeble organs. In the Archaeopteryx, a fossil
bird which agrees with the Pterodactyles in retaining the separate
condition of the metacarpal bones and in having the same number of
phalanges in two of the fingers of the fore limb, the terminal claws are
rather more compressed from side to side, and stronger than in the
Ostrich, but not nearly so strong as in the Pterodactyle. The
Archaeopteryx differs from the Pterodactyle in having no trace of a wing
finger. The first metacarpal bone is short, as in all birds; and the
first phalange scarcely lengthens that segment of the first digit of the
Bird's hand to the same length as the other metacarpal bones. It
therefore was not bent backward like the first digit in Pterodactyles.
The wing finger, from which the genius of Cuvier selected the scientific
name--Pterodactyle--for these fossils, yields their most distinctive
character. It is a feature which could only be partly paralleled in the
Bat, by making changes of structure which would remove every support to
the wing but the outermost digit of that animal's hand. In the Bat's
hand the membrane for flight is extended chiefly by four diverging
metacarpal bones. There are only two or three phalanges in each digit in
its four wing fingers. In Pterodactyles the metacarpal bones are, as we
have seen, arranged in close contact, and take no part in stretching the
wing.
THE WING FINGER
In Birds there is nothing whatever to represent the wing finger of the
Pterodactyle, for it is an organ external to the finger bones of the
bird, and contains four phalanges. The first phalange is quite different
from the others. Its length is astonishing when compared with the small
phalanges of the clawed fingers. The articular surface, which joins on
to the wing metacarpal bone, is a concave articulation, which fits the
pulley in which that bone ends. The pulley articulation admits of an
extension movement in one direction only. Many specimens show the wing
finger to be folded up so as to extend backward. The whole finger is
preserved in other specimens straightened out so as to be in line with
the metacarpus. This condition is well seen in Professor Marsh's
specimen of Rhamphorhynchus, which has the wing membrane preserved, in
which all bones of the fore-arm metacarpus and wing finger are extended
in a continuous curve. The outer surface of the end of the first bone of
the wing finger overlaps the wing metacarpal, so that a maximum of
strength and resistance is provided in the bony structures by which the
wing is supported. There is, therefore, in flight only one angular bend
in the limb, and that is between the upper arm bone and the fore-arm.
An immense pneumatic foramen is situate in a groove on the under side of
the upper end of the first phalange in Ornithocheirus, but is absent in
specimens from the Kimeridge clay. This bone is long and stout. It
terminates at the lower end in an obliquely truncated articular surface.
Specimens occur in the Cambridge Greensand which are 2 inches broad at
the upper end and nearly 1-1/2 inch wide at the lower end. An imperfect
bone from the Chalk is 14-1/2 inches long. The bones are all flattened.
Specimens from the Chalk of Kansas at Munich are 28 inches long. The
second phalange is concave at the upper articular end and convex in the
longer direction at the lower end. The articular points of union between
the several phalanges form prominences on the under side of the finger
in consequence of the adjacent bones being a little widened at their
junction. It should be mentioned that there is a proximal epiphysis or
separate bone to the first phalange, adjacent to the pulley joint of the
metacarpal bone, which is like the separate olecranon process of the
ulna of the fore-arm. It sometimes comes away in specimens from the
Chalk and Cambridge Greensand, leaving a large circular pit with a
depressed narrow border. On the outer side of this process is a rounded
boss, which may possibly have supported the bone, if it were applied to
the ground with the wing folded up, like the wing of a Bat directed
upward and backward at the animal's side.
The four bones of the wing finger usually decrease progressively in
length, so that in Rhamphorhynchus, in which the length of the animal's
head only slightly exceeds 3-1/2 inches, the first phalange is nearly as
long, the second phalange is about 3-1/4 inches, the third 2-3/4 inches,
and the fourth a little over 2 inches. Thus the entire length of the
four phalanges slightly exceeds 11 inches, or rather more than three
times the length of the head. But the fore-arm and metacarpus in this
type only measure 3 inches. Therefore the entire spread of wings could
not have been more than 2 feet 9 inches.
The largest Ornithosaur in which accurate measurements have been made is
the toothless Pterodactyle Ornithostoma, also named Pteranodon, from
North America. In that type the head appears to have been about 3 or 4
feet long, and the wing finger exceeded 5 feet; while the length of the
fore-arm and metacarpus exceeded 3 feet. The width of the body would not
have been more than 1 foot. The length of the short humerus, which was
about 11 inches, did not add greatly to the stretch of the wing; so that
the spread of the wings as stretched in flight may be given as probably
not exceeding 17 or 18 feet. A fine example of the wing bones of this
animal quite as large has been obtained by the (British Museum Natural
History). Many years ago, on very fragmentary materials, I estimated the
wings in the English Cretaceous Ornithocheirus as probably having a
stretch of 20 feet in the largest specimens, basing the calculation
partly upon the extent of the longest wings in existing birds relatively
to their bones, and partly upon the size of the largest associated bones
which were then known.
CHAPTER XII
EVIDENCES OF THE ANIMAL'S HABITS FROM ITS REMAINS
Such are the more remarkable characters of the bones in a type of animal
life which was more anomalous than any other which peopled the earth in
the Secondary Epoch of geological time. Its skeleton in different parts
resembles Reptiles, Birds, and Mammals; with modifications and
combinations so singular that they might have been deemed impossible if
Nature's power of varying the skeleton could be limited. Since
Ornithosaurs were provided with wings, we may believe the animals to
some extent to have resembled birds in habit. Their modes of progression
were more varied, for the structures indicate an equal capacity for
movement on land as a biped, or as a quadruped, with movement in the
air. There is little evidence to support the idea that they were usually
aquatic animals. The majority of birds which frequent the water have
their bodies stored with fat and the bones of their extremities filled
with marrow. And a bird's marrow bones are stouter and stronger than
those which are filled with air. There are few, if any, bones of
Pterodactyles so thick as to suggest the conclusion that they contained
marrow, and the bones of the extremities appear to have been
constructed on the lightest type found among terrestrial birds. Their
thinness, except in a few specimens from the Wealden rocks, is
marvellous; and all the later Pterodactyles show the arrangement, as in
birds, by which air from the lungs is conveyed to the principal bones.
No Pterodactyle has shown any trace of the web-footed condition seen in
birds which swim on the water, unless the diverging bones of the hind
foot in Rhamphorhynchus supports that inference. The bones of the hind
foot are relatively small, and if it were not that a bird stands easily
upon one foot, might be considered scarcely adequate to support the
animal in the position which terrestrial birds usually occupy. Yet, as
compared with the length and breadth of the foot in an Ostrich, the toes
of an Ornithosaur are seen to be ample for support. These facts appear
to discourage the idea that the animals were equally at home on land and
water, and in air.
Some light may be thrown upon the animal's habits by the geological
circumstances under which the remains are found. The Pterodactyle named
Dimorphodon, from the Lias of the south of England, is associated with
evidences of terrestrial land animals, the best known of which is
Scelidosaurus, an armoured Dinosaur adapted by its limbs for progression
on land. And the Pterodactyle Campylognathus, from the Lias of Whitby,
is associated with trunks of coniferous trees and remains of Insects. So
that the occurrence of Pterodactyles in a marine stratum is not
inconsistent with their having been transported by streams from off the
old land surface of the Lias, on which coniferous trees grew and
Dinosaurs lived.
Similar considerations apply to the occurrence of the Rhamphocephalus in
the Stonesfield Slate of England. The deposit is not only formed
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