Dragons of the Air Part 11

When staying at Swanage, in Dorsetshire, many years ago, I had the rare good fortune to obtain from the Purbeck Beds the jaw of a Pterodactyle, which had much in common in plan with the _Cycnorhamphus Fraasii_ from the Lithographic Slate, which is preserved at Stuttgart. The tooth-bearing part of this lower jaw is 8 inches long as preserved, extending back 3 inches beyond the symphysis portion in which the two sides are blended together. It is different from Professor Fraas's specimen in having the teeth carried much further back, and in the animal being nearly twice as large. This fragment of the jaw is little more than 1 foot long, which is probably less than half its original length. A vertebra nearly 5 inches long, which is more than twice the length of the longest neck bones in the Stuttgart fossil, is the only indication of the vertebral column. Professor Owen described a wing finger bone from these Purbeck Beds, which is nearly 1 foot long. He terms it the second of the finger. It may be the third, and on the hypothesis that the animal had the proportions of the Solenhofen fossil just referred to, the first wing finger bone of the English Purbeck Pterodactyle would have exceeded 2 feet in length, and would give a length for the wing finger of about 5 feet 3 inches. For this animal the name Doratorhynchus was suggested, but at present I am unable to distinguish it satisfactorily from Cycnorhamphus, which it resembles in the forms both of the neck bones and of the jaw. Very small Pterodactyles are also found in the English Purbeck strata, but the remains are few, and scattered, like these larger bones.

[Ill.u.s.tration: FIG. 65. THE LONGEST KNOWN NECK VERTEBRA

From the Purbeck Beds of Swanage. (Half natural size)]

ORNITHODESMUS LATIDENS

[Ill.u.s.tration: FIG. 66. CERVICAL VERTEBRA OF ORNITHODESMUS

From the Wealden Beds of the Isle of Wight]

The Wealden strata being shallow, fresh-water deposits might have been expected to supply better knowledge of Pterodactyles than has. .h.i.therto been available. Jaws of Ornithocheirus sagittirostris have been found in the beds at Hastings, and in other parts of Suss.e.x. Some fragments are as large as anything known. The best-preserved remains have come from the Isle of Wight, and were rewards to the enthusiastic search of the Rev. W. Fox, of Brixton. In the princ.i.p.al specimen the teeth were short and wide, the head large and deep with large vacuities, but the small brain case of that skull is bird-like. The neck bones are 2-1/2 inches long. In the upper part of the back the bones are united together by anchylosis, so that they form a structure in the back like a sacrum, which does not give attachment to the scapula, as in some Pterodactyles from the Chalk, but the bones are simply blended, as in the frigate-bird, allied to Pelicans and Cormorants. And then after a few free vertebrae in the lower part of the back, succeeds the long sacrum, formed in the usual way, of many vertebrae. I described a sacrum of this type from the Wealden Beds, under the name _Ornithodesmus_, referable to another species, which in many respects was so like the sacrum of a Bird that I could not at the time separate it from the bird type. This genus has a sternum with a strong deep keel, and the articulation for the coracoid bones placed at the back of the keel in the usual way, but with a relation to each other seen in no genus. .h.i.therto known, for the articular surfaces are wedge-shaped instead of being ovate; and instead of being side by side, they obliquely overlap, practically as in wading birds like the Heron. I have never seen any Pterodactyle teeth so flattened and shaped like the end of a lancet; and from this character the form was known between Mr. Fox and his friends as "latidens." The name Ornithodesmus is as descriptive of the sternum as of the vertebral column. The wing bones, as far as they are preserved, have the relatively great strength in the fore limb which is found in many of the Pterodactyles of the Cretaceous period, and are quite as large as the largest from the Cambridge Greensand. In the Suss.e.x species named _P.

sagittirostris_ the lower jaw articulation was inches wide.

[Ill.u.s.tration: FIG. 67. STERNUM OF _ORNITHODESMUS_

Showing the overlapping facets for the coracoid bones (shaded) behind the median keel]

[Ill.u.s.tration: FIG. 68. FRONT OF THE KEEL OF THE STERNUM OF _ORNITHODESMUS LATIDENS_

Showing also the articulation for the coracoid bone]

A few Pterodactyles' bones have been discovered in the Neocomian sands of England and Germany, and other larger bones occur in the Gault of Folkestone and the north of France; but never in such a.s.sociation as to throw light on the aspect of the skeleton.

ORNITHOCHEIRUS

Within my own memory Pterodactyle remains were equally rare from the Cambridge Greensand. The late Professor Owen in one of his public lectures produced the first few fragments received from Cambridge, and with a knowledge which in its scientific method seemed to border on the power of creation, produced again the missing parts, so that the bones told their story, which the work of waves and mineral changes in the rock had partly obliterated. Subsequently good fortune gave me the opportunity during ten years to help my University in the acquisition and arrangement of the finest collection of remains of these animals in Europe. Out of an area of a few acres, during a year or two, came the thousand bones of Ornithosaurs, mostly a.s.sociated sets of remains, each a part of a separate skeleton, described in my published catalogues, as well as the best of those at York and in the British Museum and other collections in London.

The deposit which yields them, named Cambridge Greensand, may or may not represent a long period of time in its single foot of thickness; but the abundance of fossils, obtained whenever the workmen were adequately remunerated for preserving them, would suggest that the Pterodactyles might have lived like sea-birds or in colonies like the Penguins, if it were not that the number of examples of each species found is always small, and the many variations of structure suggested rather that the individuals represent the life of many lands. The collections of remains are mostly from villages in the immediate vicinity of Cambridge, such as Chesterton, Huntingdon Road, Coldham Common, Haslingfield, Barton, Shillington, Ditton, Granchester, Harston, Barrington, stretching south to Ashwell in Bedfordshire on the one hand, as well as further north by Horningsea into the fens. Each appears to be the a.s.sociated bones of a single individual. The remains mostly belong to comparatively large animals. Some were small, though none have been found so diminutive as the smallest from the Solenhofen Slate. The largest specimens with long jaws appear to have had the head measuring not more than eighteen inches in length, which is less than half the size of the great toothless Pterodactyles from Kansas.

[Ill.u.s.tration: FIG. 69. RESTORATION OF THE SKULL OF ORNITHOCHEIRUS

The parts left white are in the Geological Museum at Cambridge. The shaded parts have not been found. The two holes are the eye and the nostril (From the Cambridge Greensand)]

The Cambridge specimens manifestly belong to at least three genera.

Something may be said of the characters of the large animals which are included in the genus Ornithocheirus. These fossils have many points of structure in common with the great American toothless forms which are of similar geological age. The skull is remarkable for having the back of the head prolonged in a compressed median crest, which rose above the brain case, and extended upward and over the neck vertebrae, so as to indicate a muscular power not otherwise shown in the group. For about three inches behind the brain this wedge of bone rested on the vertebrae, and probably overlapped the first three neural arches in the neck.

Another feature of some interest is the expansion of the bone which comes below the eye. In Birds this malar or cheek bone is a slender rod, but in these Pterodactyles it is a vertical plate, which is blended with the bone named the quadrate bone, which makes the articulation with the lower jaw in all oviparous animals.

The beak varies greatly in length and in form, though it is never quite so pointed as in the American genus, for there is always a little truncation in front, when teeth are seen projecting forward from a position somewhat above the palate; the snout is often ma.s.sive and sometimes club-shaped. Except for these variations of shape in the compressed snout, which is characterised by a ridge in the middle of the palate, and a corresponding groove in the lower jaw, and the teeth, there is little to distinguish what is known of the skull in its largest English Greensand fossils from the skull remains which abound in the Chalk of Kansas.

This English genus Ornithocheirus, represented by a great number of species, had the neural arch of the neck bones expanded transversely over the body of the vertebra in a way that characterises many birds with powerful necks, and is seen in a few Pterodactyles from Solenhofen.

It is difficult to resist the conclusion that the neck vertebrae were not usually more than twice to three times as long as those of the back, and it would appear that the caudal vertebrae in the English Cretaceous types were comparatively large, and about twice as long as the dorsal vertebrae. Unless there has been a singular succession of accidents in the a.s.sociation of these vertebrae with the other remains, Ornithocheirus had a tail of moderate length, formed of a few vertebrae as long as those of the neck, though more slender, quite unlike the tail in either the long-tailed or short-tailed groups of Solenhofen Pterodactyles, and longer than in the toothless Pterodactyles of America.

[Ill.u.s.tration: FIG. 70. CERVICAL VERTEBRA, ORNITHOCHEIRUS

Under side, half natural size. (Cambridge Greensand)]

The singular articulation for the humerus at the truncated extremity of the coracoid bone is a character of this group, as is the articulation of the scapulae with the neural arches of the dorsal vertebrae, at right angles to them (p. 115), instead of running over the ribs as in Birds and as in other Pterodactyles.

The smaller Pterodactyles have their jaws less compressed from side to side. The upper arm bone, the humerus, instead of being truncated at its lower end as in Ornithocheirus, is divided into two or three rounded articular surfaces. That for the radius, the bone which carries the wrist, is a distinct and oblique rounded facet, while the ulna has a rounded and pulley-like articulation on which the hand may rotate. These differences are probably a.s.sociated with an absence of the remarkable mode of union of the scapulae with the dorsal vertebrae. But I have hesitated to give different names to these smaller genera because no example of scapula has come under my notice which is not truncated at the free end. I do not think this European type can be the Nyctodactylus of Professor Marsh, in which sutures appear to be persistent between the bodies of the vertebrae and their arches, because no examples have been found at Cambridge with the neural arches separated, although the scapula is frequently separated from the coracoid in large animals.

[Ill.u.s.tration: FIG. 71. UPPER AND LOWER JAWS OF AN ENGLISH PTERODACTYLE FROM THE CHALK, AS PRESERVED]

ORNITHOSTOMA

[Ill.u.s.tration: FIG. 72. THE PALATE OF THE ENGLISH TOOTHLESS PTERODACTYLE, ORNITHOSTOMA]

[Ill.u.s.tration: FIG. 73. TYPES OF THE AMERICAN TOOTHLESS PTERODACTYLE, ORNITHOSTOMA

Named by Marsh, Pteranodon]

The most interesting of all the English Pterodactyle remains is the small fragment of jaw figured by Sir Richard Owen in 1859, which is a little more than two inches long and an inch wide, distinguished by a concave palate with smooth rounded margins to the jaws and a rounded ridge to the beak. It is the only satisfactory fragment of the animal which has been figured, and indicates a genus of toothless Pterodactyles, for which the name Ornithostoma was first used in 1871.

After some years Professor Marsh found toothless Pterodactyles in Kansas, and indicated several species. There are remains to the number of six hundred specimens of these American animals in the Yale Museum alone; but very little was known of them till Professor Williston, of Lawrence, in Kansas, described the specimens from the Kansas University Museum, when it became evident that the bones of the skeleton are mostly formed on the same plan as those of the Cambridge Greensand genus, Ornithocheirus. They are not quite identical. Professor Williston adopts for them the name Ornithostoma, in preference to Pteranodon which Marsh had suggested. Both animals have the dagger-shaped form of jaw, with corresponding height and breadth of the palate. The same flattened sides to the snout, converging upwards to a rounded ridge, the same compressed rounded margin to the jaw, which represents the border in which teeth are usually implanted, and in both the palate has the same smooth character forming a single wide concave channel. Years previously I had the pleasure of showing to Professor Marsh the remarkable characters of the jaw, shoulder-girdle bones, and scapulae in the Greensand Pterodactyles while the American fossils were still undiscovered. I subsequently made the restoration of the shoulder-girdle (p. 115).

Professor Williston states to me that the shoulder-girdle bones in American examples of Ornithostoma have a close resemblance to those of Ornithocheirus figured in 1891, as is evident from remains now shown in the British Museum. It appears that the Kansas bones are almost invariably crushed flat, so that their articular ends are distorted. The neck vertebrae are relatively stout as in Ornithocheirus. The hip-girdle of the American Ornithostoma can be closely paralleled in some English specimens of Ornithocheirus, though each prepubic bone is triangular in the American fossils as in _P. rhamphastinus_. They are united into a transverse bar as in Rhamphorhynchus, unknown in the English fossils.

The femur has the same shape as in Ornithocheirus; and the long tibia terminates in a pulley. There is no fibula. The sternum in both has a manubrium, or thick keel ma.s.s, prolonged in front of its articular facets for the coracoid bones, which are well separated from each other.

Four ribs articulate with its straight sides. The animal has four toes and the fifth is rudimentary; there are no claws to the first and second.

[Ill.u.s.tration: FIG. 74. RESTORATION OF THE SKELETON OF _ORNITHOSTOMA INGENS_ (MARSH)

From the Niobrara Cretaceous of Western Kansas. Made by Professor Williston. The original has a spread of wing of about 19 feet 4 inches. Fragments of larger individuals are preserved at Munich]

In the restoration which Professor Williston has made the wing metacarpal is long, and in the shortest specimen measures 1 foot 7 inches, and in the longest 1 foot 8 inches. This is exactly equal to the length of the first phalange of the wing finger. The second wing finger bone is 3 inches shorter, the third is little more than half the length of the first, while the fourth is only 6-3/4 inches long, showing a rapid shortening of the bones, a condition which may have characterised all the Cretaceous Pterodactyles. The short humerus, about 1 foot long, and the fore-arm, which is scarcely longer, are also characteristic proportions of Ornithostoma or Pteranodon, as known from the American specimens. Professor Williston gives no details of the remarkable tail, beyond saying that the tail is small and short, and that the vertebrae are flat at the ends, without transverse processes. In the restoration the tail is shorter than in the short-tailed species from the Lithographic Slate, and unlike the tail in Ornithocheirus.

This is the succession of Pterodactyles in geological time. Their history is like that of the human race. In the most ancient nations man's life comes upon us already fully organised. The Pterodactyles begin, so far as isolated bones are concerned, in the Rhaetic strata; perhaps in the Muschelkalk or middle division of the Trias. And from the beginning of the Secondary time they live on with but little diversity in important and characteristic structures, and so far as habit goes, the great Pterodactyles of the Upper Chalk of England cannot be said to be more highly organised than the earlier stiff-tailed genera of the Lias or the Oolites. There is nothing like evolution. No modification such as that which derives the one-toed horse or the two-toed ox from ancestors with a larger number of digits. On the other hand, there is little, if any, evidence of degeneration. The later Pterodactyles do not appear to have lost much, although the tail in some of the Solenhofen genera may be degenerate when compared with the long tail of Dimorphodon; but the short-tailed types are found side by side with the long-tailed Rhamphorhynchus. The absence of teeth may be regarded as degeneration, for they have presumably become lost, in the same way that Birds now existing have lost the teeth which characterised the fossil birds--Ichthyornis of the American Greensand, and Archaeopteryx of the Upper Oolites of Bavaria. But just as some of the earlier Pterodactyles have no teeth at the extremity of the jaw, such as Dorygnathus and Rhamphorhynchus, so the loss of teeth may have extended backward till the jaws became toothless. The specimens. .h.i.therto known give no evidence of such a change being in progress. But just as the division of Mammals termed Edentata usually wants only the teeth which characterise the front of the jaw, yet others, like the Great Ant-eater of South America named Myrmecophaga, have the jaws as free from teeth as the toothless Pterodactyles or living Birds, and show that in that order the teeth have no value in separating these animals into subordinate groups any more than they have among the Monotremata, where one type has teeth and the other is toothless.

The following table gives a summary of the Geological History and succession in the Secondary Rocks of the princ.i.p.al genera of Flying Reptiles.

-----------------------+---------------------------------------------- NAMES OF THE GENERA.

GEOLOGICAL FORMATIONS. +-----------------------+---------------------- British and European. North American.

-----------------------+-----------------------+---------------------- Upper Chalk } Ornithostoma } (_Pteranodon_) Lower Chalk } Ornithocheirus } Nyctodactylus Upper Greensand } Ornithostoma Gault -----------------------+ Lower Greensand Wealden Ornithodesmus Purbeck Doratorhynchus -----------------------+ Portland { Pterodactylus { Ptenodracon Kimeridge Clay and { Cycnorhamphus Solenhofen Slate { Diopecephalus { Rhamphorhynchus Coralline Oolite { Scaphognathus Oxford Clay -----------------------+ Great Oolite and Stonesfield Slate Rhamphocephalus Inferior Oolite -----------------------+ Upper Lias { Campylognathus { Dorygnathus Lower Lias Dimorphodon -----------------------+ Rhaetic bones Muschelkalk ? bones -----------------------+-----------------------+----------------------

CHAPTER XVI

CLa.s.sIFICATION OF THE ORNITHOSAURIA

When an attempt is made to determine the place in nature of an extinct group of animals and the relation to each other of the different types included within its limits, so as to express those facts in a cla.s.sification, attention is directed in the first place to characters which are constant, and persist through the whole of its const.i.tuent genera. We endeavour to find the structural parts of the skeleton which are not affected by variation in the dent.i.tion, or the proportions of the extremities, or length of the tail, which may define families or genera, or species.

It has already been shown that while in many ways the Ornithosaurian animals are like Birds, they have also important resemblances to Reptiles. They are often named Pterosauria. The wing finger gives a distinctive character which is found in neither one cla.s.s of existing animals nor the other, and is common to all the Pterodactyles at present known. They have been named Ornithosauria as a distinct minor division of back-boned animals, which may be regarded as neither Reptiles nor Birds in the sense in which those terms are used to define a Lizard or Ostrich among animals which still exist. It is not so much that they mark a transition from Reptile to Bird, as that they are a group which is parallel to Birds, and more manifestly holds an intermediate place than Birds do between Reptiles and Mammals. In plan of structure Bird and Reptile have more in common than was at one time suspected. The late Professor Huxley went so far as to generalise on those coincidences in parts of the skeleton, and united Birds and Reptiles into one group, which he named Sauropsida, to express the coincidences of structure between the Lizard and the Bird tribes. The idea is of more value than the term in which it is expressed, because Reptiles are not, as we have seen, a group of animals which can be defined by any set of characters as comprehensive as those which express the distinctive features of Birds. From the anatomist's point of view Birds are a smaller group, and while some Reptiles have affinity with them, it is rather the extinct than the living groups which indicate that relation. Other Reptiles have affinities of a more marked kind with Mammals, and there are points in the Ornithosaurian skeleton which are distinctly Mammalian. So that when the Monotreme Mammals are united with South African reptiles known as Theriodontia, which resemble them, in a group termed Theropsida to express their mammalian resemblances, it is evident that there is no one continuous chain of life or gradation in complexity of structure of animals.