CHAPTER XV

ORNITHOSAURS FROM THE UPPER SECONDARY ROCKS

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.

The Wealden strata being shallow, fresh-water deposits might have been expected to supply better knowledge of Pterodactyles than has hitherto been available. Jaws of Ornithocheirus sagittirostris have been found in the beds at Hastings, and in other parts of Sussex. 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 principal 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 2½ 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 vertebræ in the lower part of the back, succeeds the long sacrum, formed in the usual way, of many vertebræ. 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 hitherto 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 Sussex species named P. sagittirostris the lower jaw articulation was inches wide.

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 association 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 associated 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 associated 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.

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 vertebræ, 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 vertebræ, 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 massive 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 vertebræ were not usually more than twice to three times as long as those of the back, and it would appear that the caudal vertebræ in the English Cretaceous types were comparatively large, and about twice as long as the dorsal vertebræ. Unless there has been a singular succession of accidents in the association of these vertebræ with the other remains, Ornithocheirus had a tail of moderate length, formed of a few vertebræ 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.

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 scapulæ with the neural arches of the dorsal vertebræ, 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 associated with an absence of the remarkable mode of union of the scapulæ with the dorsal vertebræ. 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 vertebræ 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.

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 scapulæ 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 vertebræ 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 mass, 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.

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 6¾ 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 vertebræ 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 Rhætic 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 Archæopteryx 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 hitherto 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 principal genera of Flying Reptiles.

CHAPTER XVI

CLASSIFICATION OF THE ORNITHOSAURIA

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 class 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.

We have to determine whether the Ornithosauria incline towards the Sauropsidan or Bird-Reptile alliance, or to the Mammal-Reptile or Theropsidan alliance. There can be no doubt that the predominant tendency is to the former, with a minor affinity towards the latter.

The Ornithosauria are one of a series of groups of animals, living and extinct, which have been combined in an alliance named the Ornithomorpha. That group includes at least five great divisions of animals, which circle about birds, known as Ornithosauria, Crocodilia, Saurischia, Aves, Ornithischia, and Aristosuchia. Their relations to each other are not evident in an enumeration, but may be shown in some degree in a diagram (see p. 190).

THE ORNITHOMORPHA

The Ornithomorpha arranged in this way show that the three middle groups—carnivorous Saurischia, Aristosuchia, herbivorous Ornithischia—which are usually united as Dinosauria, intervene between Birds and Ornithosaurs; and that the Crocodilia and Ornithosauria are parallel groups which are connected with Birds, by the group of Dinosaurs, which resembles Birds most closely.

The Ornithomorpha is only one of a series of large natural groups of animals into which living and extinct terrestrial vertebrata may be arranged. And the succeeding diagram may contribute to make evident the relations of Ornithosauria to the other terrestrial vertebrata (see p. 191).

Herein it is seen that while the Ornithomorpha approach towards Mammalia through the Ornithosauria, and less distinctly through the Crocodilia, they approach more directly to the Sauromorpha, through the Plesiosaurs and Hatteria; while that group also approaches more directly to the Mammals through the Plesiosaurs and Anomodonts.

Diagram of the Affinities of the Orders of Animals comprised in the Ornithomorpha.

The Aristosuchia is imperfectly known, and therefore to some extent a provisional group. It is a small group of animals.

Diagram showing the Relations of the Ornithomorpha to the chief large groups of Terrestrial Vertebrata,
and their affinities with each other.

Cordylomorpha are Ichthyosaurs and the Labyrinthodont group. Herpetomorpha include Lacertilia, Homœosauria, Dolichosauria, Chameleonoidea, Ophidia, Pythonomorpha.

The Sauromorpha comprises the groups of extinct and living Reptiles named Chelonia, Rhynchocephala, Sauropterygia, Anomodontia, Nothosauria, and Protorosauria. These details may help to explain the place which has been given to the Ornithosauria in the classification of animals.

Turning to the Pterodactyles themselves, Von Meyer divided them naturally into short-tailed and long-tailed. The short-tailed indicated by the name Pterodactylus he further divided into long-nosed and short-nosed. The short-nosed genus has since been named Ptenodracon (Fig. 59, p. 167). The long-tailed group was divided into two types—the Rhamphorhynchus of the Solenhofen Slate (Fig. 56, p. 161) and the English form now known as Dimorphodon (Fig. 52, p. 150), which had been described from the Lias.

The Cretaceous Pterodactyles form a distinct family. So that, believing the tail to have been short in that group (Fig. 58), there are two long-tailed as well as two short-tailed families, which were defined from their typical genera Pterodactylus, Ornithocheirus, Rhamphorhynchus, and Dimorphodon.

The differences in structure which these animals present are, first: the big-headed forms from the Lias like Dimorphodon, agree with the Rhamphorhynchus type from Solenhofen in having a vacuity in the skull defined by bone, placed between the orbit of the eye and the nostril. With those characters are correlated the comparatively short bones which correspond to the back of the hand termed metacarpals, and the tail is long, and stiffened down its length with ossified tendons. These characters separate Ornithosaurs with long tails from those with short tails.

The short-tailed types represented by Pterodactylus and Ornithocheirus have no distinct antorbital vacuity in the skull defined by bone. The metacarpal bones of the middle hand are exceptionally elongated, and the tail, which was flexible in both, appears to have been short. These differences in the skeleton warrant a primary division of flying reptiles into two principal groups.

The short-tailed group, which was recognised by De Blainville as intermediate between Birds and Reptiles, may take the name Pterodactylia, which he suggested as a convenient, distinctive name. It may probably be inconvenient to enlarge its significance to comprise not only the true Pterodactyles originally defined as Pterosauria, but the newer Ornithostoma and Ornithocheirus which have been grouped as Ornithocheiroidea.

The second order, in which the wing membrane appears to have had a much greater extent, in being carried down the hind limbs, where the outermost digit and metatarsal are modified for its support, has been named Pterodermata, to include the types which are arranged around Rhamphorhynchus and Dimorphodon.

Both these principal groups admit of subdivision by many characters in the skeleton, the most remarkable of which is afforded by the pair of bones carried in front of the pubes, and termed prepubic bones. In the Pterodactyle family the bones in front of the pubes are always separate from each other, always directed forward, and have a peculiar fan-shaped form with concave sides like the bone which holds a similar position in a Crocodile. In the Ornithocheirus family the prepubic bones appear to have been originally triangular, but were afterwards united so as to form a strong continuous bar which extends transversely across the abdomen in advance of the pubic bones. This at least is the distinctive character in the genus Ornithostoma according to Professor Williston, which in many ways closely resembles Ornithocheirus.

The two families in the long-tailed order named Pterodermata are separated from each other by a similar difference in their prepubic bones. In Dimorphodon those bones are separate from each other, and remain distinct through life, meeting in the middle line of the body in a wide plate. On the other hand, in Rhamphorhynchus the prepubic bones, which are at first triangular and always slender, become blended together into a slight transverse bar, which only differs from that attributed to Ornithostoma in its more slender bow-shaped form.

Thus if other characters of the skeleton are ignored and a classification based upon the structure of the pelvis and prepubic bones, there would be some ground for associating the long-tailed Rhamphorhynchus from the Upper Oolites which is losing the teeth in the front of its jaw with the Cretaceous Ornithostoma, which has the teeth completely wanting; while the long-tailed Dimorphodon would come into closer association with the short-tailed Pterodactylus. The drum-stick bone or tibia in Dimorphodon, with its slender fibula, like that of a Bird, also resembles a Bird in the rounded and pulley-shaped terminal end which makes the joint corresponding to the middle of the ankle bones in man. The same condition of a terminal pulley joint is found in the Cretaceous Pterodactyles. But in the true Pterodactyles and in Rhamphorhynchus there usually is no pulley-shaped termination to the lower end of the drum-stick, for the tarsal bones remain separate from each other, and form two rows of ossifications, showing the same differences as separate Dinosaurs into the divisions which have been referred to, from their Bird-like pelvis and tibio-tarsus, as Ornithischia in the one case, and Saurischia in the other from their bones being more like those of living Lizards.

CHAPTER XVII

FAMILY RELATIONS OF PTERODACTYLES TO ANIMALS WHICH LIVED WITH THEM

Enough has been said of the general structure of Pterodactyles and the chief forms which they assumed while the Secondary rocks were accumulating, to convey a clear idea of their relations to the types of vertebrate animals which still survive on the earth. We may be unable to explain the reasons for their existence, and for their departure from the plan of organisation of Reptiles and Birds. But the evidence has not been exhausted which may elucidate their existence. Sometimes, in problems of this kind, which involve comparison of the details of the skeleton in different animals, it is convenient to imagine the possibility of changes and transitions which are not yet supported by the discovery of fossil remains. If, for example, the Pterodactyle be conceived of as divested of the wing finger, which is its most distinctive character, or that finger is supposed to be replaced by an ordinary digit, like the three-clawed digits of the hand which we have regarded as applied to the ground, where, it may be asked, would the animal type be found which approximates most closely to a Pterodactyle which had been thus modified? There are two possible replies to such a question, suggested by the form of the foot. For the old Bird Archæopteryx has three such clawed digits, but no wing finger. And some Dinosaurs also have the hand with three digits terminating in claws, which are quite comparable to the clawed digits of Pterodactyles.

The truth expressed in the saying that no man by taking thought can add a cubit to his stature is of universal application in the animal world, in relation to the result upon the skeleton of the exercise of a function by the individual. Yet such is the relation in proportions of the different parts of the animal to the work which it performs, so marked is the evidence that growth has extended in direct relation to use of organs and active life, and that structures have become dwarfed from overwork, or have wasted away from disuse—seen throughout all vertebrate animals, that we may fairly attribute to the wing finger some correlated influence upon the proportions of the animal, as a consequence of the dependence of the entire economy upon each of its parts. Therefore if an allied animal did not possess a wing finger, and did not fly, it might not have developed the lightness of bone, or the length of limb which Pterodactyles possess.

The mere expansion of the parachute membrane seen in so-called flying animals, both Mammals and Reptiles, which are devoid of wings, is absolutely without effect in modifying the skeleton. But when in the Bat a wing structure is met with which may be compared to a gigantic extension of the web foot of the so-called Flying Frog, the bones of the fingers and the back of the hand elongate and extend under the stimulus of the function of flight in the same way as the legs elongate in the more active hoofed animals, with the function of running. Therefore it is not improbable that the limbs shared to some extent in growth under stimulus of exercise which developed the wing finger. And if an animal can be found among fossils so far allied as to indicate a possible representative of the race from which these Flying Dragons arose, it might be expected to be at least shorter legged, and possibly more distinctly Reptilian in the bones of the shoulder-girdle which support the muscles used in flight. It may readily be understood that the kinds of life which were most nearly allied to Pterodactyles are likely to have existed upon the earth with them, and that flight was only one of the modes of progression which became developed in relation to their conditions of existence. The principal assemblage of terrestrial animals available for such comparison is the Dinosauria. They may differ from Pterodactyles as widely as the Insectivora among Mammals differ from Bats, but not in a more marked way. Comparisons will show that there are resemblances between the two extinct groups which appeal to both reason and imagination.

Dinosaurs are conveniently divided by characters of the pelvis first into the order Saurischia, which includes the carnivorous Megalosaurus and the Cetiosaurus, with the pelvis on the Reptile plan; and secondly the order Ornithischia, represented by Iguanodon, with the pelvis on the Bird plan. It may be only a coincidence, but nevertheless an interesting one, that the characters of those two great groups of reptiles, which also extend throughout the Secondary rocks, are to some extent paralleled in parts of the skeleton of the two divisions of Pterodactyles. This may be illustrated by reference to the skull, pelvis, hind limb, and the pneumatic condition of the bones.

The Saurischian Dinosauria have an antorbital vacuity in the side of the skull between the nasal opening and the eye, as in the long-tailed Ornithosaurs named Pterodermata. In some of the older genera of these carnivorous Dinosaurs of the Trias, the lateral vacuities of the head are as large as in Dimorphodon. But in some at least of the Iguanodont, or Ornithischian Dinosaurs, there is no antorbital vacuity, and the side of the face in that respect resembles the short-tailed Pterodactylia. The skull of a carnivorous Dinosaur possesses teeth which, though easily distinguished from those of Pterodactyles, can be best compared with them. The most striking difference is in the fact that in the Dinosaur the nostrils are nearly terminal, while in the Pterodactyle they are removed some distance backward. This result is brought about by growth taking place, in the one case at the front margin of the maxillary bone so as to carry the nostril forward, and in the other case at the back margin of the premaxillary bone. Thus an elongated part of the jaw is extended in front of the nostril. Hence there is a different proportion between the premaxillary and maxillary bones in the two groups of animals, which corresponds to the presence of a beak in a bird, and its absence in living reptiles. It is not known whether the extremity of the Pterodactyle's beak is a single bone, the intermaxillary bone, such as forms the corresponding toothless part of the jaw in the South African reptile Dicynodon, or whether it is made by the pair of bones called premaxillaries which form the extremity of the jaw in most Dinosaurs. Too much importance may perhaps be attached to such differences which are partly hypothetical, because the extinct Ichthyosaurus, which has an exceptionally long snout, has the two premaxillary bones elongated so as to extend backward to the nostrils. A similar elongation of those bones is seen in Porpoises, which also have a long snout; and the bones are carried back from the front of the head to the nostrils, which are sometimes known as blowholes. But the Porpoise has those premaxillary bones not so much in advance of the bones which carry teeth named maxillary, as placed in the interspace between them. The nostrils, however, are not limited to the extremity of the head in all Dinosaurs. If this region of the beak in Dimorphodon be compared with the corresponding part of a Dinosaur from the Permian rocks, or Trias, the relation of the nostril to the bones forming the beak may be better understood.

In the sandstone of Elgin, usually named Trias, a small Dinosaur is found, which has been named Ornithosuchus, from the resemblance of its head to that of a Bird. Seen from above, the head has a remarkable resemblance to the condition in Rhamphorhynchus, in the sharp-pointed beak and positions of the orbits and other openings. In side view the orbits have the triangular form seen in Dimorphodon, and the preorbital vacuities are large, as in that genus, while the lateral nostrils, which are smaller, are further forward in the Dinosaur. The differences from Dimorphodon are in the articulation for the jaw being carried a little backward, instead of being vertical as in the Pterodactyle, and the bone in front of the nose is smaller. Notwithstanding probable differences in the palate, the approximation, which extends to the Crocodile-like vacuity in the lower jaw, is such that by slight modification in the skull the differences would be substantially obliterated by which the skull of such an Ornithosaur is technically distinguished from such a Dinosaur.

The back of the skull is clearly seen in the Whitby Pterodactyle, and its structure is similar to the corresponding part of such Dinosaurs as Anchisaurus or Atlantosaurus, without the resemblance quite amounting to identity, but still far closer than is the resemblance between the same region in the heads of Crocodiles, Lizards, Serpents, Chelonians. Few of these fossil Dinosaur skulls are available for comparison, and those differ among themselves. The coincidences rather suggest a close collateral relation than prove the elaboration of one type from the other. They may have had a common ancestor.

The Trias rocks near Stuttgart have yielded Dinosaurs as unlike Pterodactyles as could be imagined, resembling heavily armoured Crocodiles, in such types as the genus Belodon. Its jaws are compressed from side to side, as in many Pterodactyles, and the nostrils are at least as far backward as in Rhamphorhynchus. Belodon has preorbital vacuities and postorbital vacuities, but the orbit of the eye is never large, as in Pterodactyles. It might not be worth while dwelling on such points in the skull if it were not that the pelvis in Belodon is a basin formed by the blending of the expanded plates of the ischium and the pubis, into a sheet of bone which more nearly resembles the same region in Pterodactyles than does the ischio-pubic region in other Dinosaurian animals like Cetiosaurus.

The backbone in a few Dinosaurs is suggestive of Pterodactyles. In such genera as have been named Cœlurus and Calamospondylus, in which the skeleton is only partially known, the neck vertebræ become elongated, so as to compare with the long-necked Pterodactyles. The cervical rib is often very similar to that type, and blended with the vertebra, as in Pterodactyles and Birds. The early dorsal vertebræ of Pterodactyles might almost be mistaken for those of Dinosaurs. The tail vertebræ of a Pterodactyle are usually longer than in long-tailed Dinosauria.

In the limbs and the bony girdles which support them there is more resemblance between Pterodactyles and Dinosaurs than might have been anticipated, considering their manifest differences in habit. Thus all Dinosaurs have the hip bone named ilium prolonged in front of the articulation for the femur as well as behind it, almost exactly as in Pterodactyles and Birds (see p. 95). There is some difference in the pubis and ischium which is more conspicuous in form than in direction of the bones. There is a Pterodactyle imperfectly preserved, named Pterodactylus dubius, in which the ischium is directed backward and the pubis downward, and the bones unite below the acetabular cavity for the head of the femur to work in, but do not appear to be otherwise connected. In Rhamphorhynchus the connexion between these two thickened bars is made by a thin plate of bone. In such a Dinosaur as the American carnivorous Ceratosaurus the two bars of the pubis and ischium remain separate and diverging, and there is no film of bone extending over the interspace between them. The development of such a bony condition would make a close approximation between the Ornithosaurian pelvis and that of those Dinosaurs which closely resemble Pterodactyles in skull and teeth.