CHAPTER XIII. Ancient Ornithosaurs From the Lias

ANCIENT ORNITHOSAURS FROM THE LIAS

Cuvier's discourse on the revolutions of the Earth made the Pterodactyle known to English readers early in the nineteenth century. Dr. Buckland, the distinguished professor of Geology at Oxford, discovered in 1829 a far larger specimen in the Lias of Lyme Regis, and it became known by a figure published by the Geological Society, and by the description in his famous Bridgewater Treatise, p. 164. This animal was tantalising in imperfect preservation. The bones were scattered in the clay, so as to give no idea of the animal's aspect. Knowledge of its limbs and body has been gradually acquired; and now, for some years, the tail and most parts of the skeleton have been well known in this oldest and most interesting British Pterodactyle.

Sir Richard Owen after some time separated the fossil as a distinct genus, named Dimorphodon; for it was in many ways unlike the Pterodactyles described from Bavaria. The name Dimorphodon indicated the two distinct kinds of teeth in the jaws, a character which is still unparalleled among Pterodactyles of newer age. There are a few large pointed, piercing and tearing teeth in the front of the jaws, with smaller teeth further back, placed among the tearing teeth in the upper jaw; while in the lower jaw the small teeth are continuous, close-set, and form a fine cutting edge like a saw.

The Dimorphodon has a short beak, a deep head, and deep lower jaw, which is overlapped by the cheek bones. The side of the head is occupied by four vacuities, separated by narrow bars of bone. First, in front, is the immense opening for the nostril, triangular in form, with the long upper side following the rounded curve of the face. A large triangular opening intervenes between the nose hole and the eye hole, scarcely smaller than the former, but much larger than the orbit of the eye. The eye hole is shaped like a kite or inverted pear. Further back still is a narrower vertical opening known as the lateral or inferior temporal vacuity. The back of the head is badly preserved. The two principal skulls differ in depth, probably from the strains under which they were pressed flat in the clay. A singular detail of structure is found in the extremity of the lower jaw, which is turned slightly downward, and terminates in a short toothless point. The head of Dimorphodon is about eight inches long.

The neck bones are of suitable stoutness and width to support the head. The bones are yoked together by strong processes. The neck was about 6 inches long, did not include more than seven bones, and appeared short owing only to the depth and size of the head. The length of the backbone which supported the ribs was also about 6 inches. Its joints are remarkably short when compared with those of the neck. The tail is about 20 inches long.

The extreme length of the animal from the tip of the nose to the end of the tail may have been 3 feet 4 inches, supposing it to have walked on all fours in the manner of a Reptile or Mammal. This may have been a common position, but Dimorphodon may probably also have been a biped. Before 1875, when the first restoration appeared in the Illustrated London News, the legs had been regarded as too short to have supported the animal, standing upon its hind limbs. They are here seen to be well adapted for such a purpose. The upper leg bone is 3-1/4 inches long, the lower leg bone is 4-1/2 inches long, and the singularly strong instep bones are firmly packed together side by side as in a leaping or jumping Mammal, and measure 1-1/2 inches in length. Dimorphodon differs from several other Pterodactyles in having the hind limb provided with a fifth outermost short instep bone, to which two toe bones are attached. These bones are elongated in a way that may be compared, on a small scale, with the elongation of the wing finger in the fore limb. The digit was manifestly used in the same way as the wing finger, in partial support of a flying membrane, though its direction may have been upward and outward, rather than inward. There is no evidence of a pulley joint between the metatarsal and the adjacent phalange.

The height of the Dimorphodon, standing on its hind legs in the position of a Bird, with the wings folded upon the body in the manner of a Bird, was about 20 inches. An ungainly, ill-balanced animal in aspect, but not more so than many big-headed birds, and probably capable of resting upon the instep bones as many birds do. The chief point of variation from the Pterodactyle wing is in the relative length of the metacarpus in Dimorphodon. It is shorter than the other bones in the wing, never exceeding 1-1/2 inches. The total length of all the arm bones down to the point where the metacarpus might have touched the ground, or where the wing finger is bent upon it, is about 9 inches, which gives a length of less than 6 inches below the upper arm bone. The four bones of the wing finger measure, from the point where the first bone bends upon the metacarpus, less than 18 inches. So that the wings could only have been carried in the manner of the wings of a Bat, folded at the side and directed obliquely over the back when the animal moved on all fours. Its body would appear to have been raised high above the ground, in a manner almost unparalleled in Reptiles, and comparable to Birds and Mammals. Dimorphodon is to be imagined in full flight, with the body extended like that of a Bird, when the wings would have had a spread from side to side of about 4 feet 4 inches. As in other animals of this group, the three claws on the front feet are larger than the similar four claws on the hind feet; as though the fingers might have functions in grasping prey, which were not shared by the toes.

The restorations give faithful pictures of the skeleton, and the form of the body is built upon the indications of muscular structure seen in the bones.

A second English Pterodactyle is found in the Upper Lias of Whitby. It is only known from an imperfect skull, published in 1888. It has the great advantage of preserving the bones in their natural relations to each other, and with a length of head probably similar to Dimorphodon shows that the depth at the back of the eye was much less; and the skull wants the arched contour of face seen in Dimorphodon. The head has the same four lateral vacuities, but the nostril is relatively small and elongated, extending partly above the oval antorbital opening, which was larger. There is thus a difference of proportion, but it is precisely such as might result from the species having the skull flatter. The head is easily distinguished by the small nostril, which is smaller than the orbit of the eye. The animal is referred to another genus. The quadrate bones which give attachment to the lower jaw send a process inward to meet the bones of the palate, which differ somewhat from the usual condition. Two bony rods extend from the quadrate bones backward and upward to the sphenoid, and two more slender bones extend from the quadrate bones forward, and converge in a #V#-shape, to define the division between the openings of the nostrils on the palate. The #V#-shaped bone in front is called the vomer, while the hinder part is called pterygoid. The bones that extend backward to the sphenoid are not easily identified. This animal is one of the most interesting of Pterodactyles from the very reptilian character exhibited in the back of the head, which appears to be different from other specimens, which are more like a bird in that region. Yet underneath this reptilian aspect, with the bony bar at the side of the temporal region of the head formed by the squamosal and quadrate bones, defining the two temporal vacuities as in Reptiles, a mould is preserved of the cavity once occupied by the brain, showing the chief details of structure of that organ, and proving that in so far as it departs from the brain of a Bird it appears to resemble the brain of a Mammal, and is unlike the brain of a Reptile.

The Pterodactyles from the Lias of Germany are similar to the English types, in so far as they can be compared. In 1878 I had the opportunity of studying those which were preserved in the Castle at Banz, which Professor Andreas Wagner, in 1860, referred to the new genus Dorygnathus. The skull is unknown, but the lower jaw, 6-1/2 inches long, is less than 2-1/2 inches wide at the articulation with the quadrate bone in the skull. The depth of the lower jaw does not exceed 1/4 inch, so that it is in marked contrast to Buckland's Dimorphodon. The symphysis, which completely blends the rami of the jaw, is short. As far as it extends it contains large tearing teeth, followed by smaller teeth behind, like those of Dimorphodon. But this German fossil appears to differ from the English type in having the front of the lower jaw, for about 3/4 inch, compressed from side to side into a sharp blade or spear, more marked than in any other Pterodactyle, and directed upward instead of downward as in Dimorphodon. Nearly all the measurements in the skeleton are practically identical with those of the English Dimorphodon, and extend to the jaw, humerus, ulna and radius, wing metacarpal, first phalange of the wing finger. The principal bones of the hind limb appear to be a little shorter; but the scapula and coracoid are slightly larger. All these bones are so similar in form to Dimorphodon that they could not be separated from the Lyme Regis species, if they were found in the same locality.

From the Lower Lias of Germany, showing the spear in front of the tooth sockets]

Just as the Upper Lias in England has yielded a second Pterodactyle, so the Upper Lias in Germany has yielded a skeleton, to which Felix Plieninger, in 1894, gave the name Campylognathus. It is an instructive skeleton, with the head much smaller than in Dimorphodon, being less than 6 inches long, but, unfortunately, broken and disturbed. A lower jaw gives the length 4-1/2 inches. Like the other Pterodactyles from the Lias, it has the extremity of the beak toothless, with larger teeth in the region of the symphysis in front and smaller teeth behind. The jaw is deeper than in the Banz specimen from the Lower Lias, but not so deep as in Dimorphodon. The teeth of the upper jaw vary in size, and there appears to be an exceptionally large tooth in the position of the Mammalian canine at the junction of the bones named maxillary and intermaxillary.

The nasal opening is small and elongated, as in the English specimen from Whitby. As in that type there is little or no indication of the convex contour of the face seen in Dimorphodon.

The neck does not appear to be preserved. In the back the vertebrae are about 3/10 inch long, so that twelve, which is the usual number, would only occupy a length of a little more than 3-1/2 inches. The tail is elongated like that of Dimorphodon, and bordered in the same way by ossified ligaments. There are thirty-five tail vertebrae. Those which immediately follow the pelvis are short, like the vertebrae of the back. But they soon elongate, and reach a maximum length of nearly 1-1/2 inches at the eighth, and then gradually diminish till the last scarcely exceeds 1/8 inch in length. The length of the tail is about 22 inches; this appears to be an inch or two longer than in Dimorphodon. The longest rib measures 2-1/2 inches, and the shortest 2 inches. These ribs probably were connected with the sternum, which is imperfectly preserved.

The bones of the limbs have about the same length as those of Dimorphodon, so far as they can be compared, except that the ulna and radius are shorter. The wing metacarpal is of about the same length, but the first phalange of the wing finger measures 6-1/4 inches, the second is about 8-1/4 inches, the third 6-1/2 inches, and the fourth 4-3/4 inches; so that the total length of the wing finger was about half an inch short of 2 feet. One character especially deserves attention in the apparent successive elongation of the first three phalanges in the wing finger in Dimorphodon. The third phalange is the longest in the only specimen in which the finger bones are all preserved. Usually the first phalange is much longer than the second, so that it is a further point of interest to find that this German type shares with Dimorphodon a character of the wing finger which distinguishes both from some members of the group by its short first phalange.

The pelvis is exceptionally strong in Campylognathus, and although it is crushed the bones manifestly met at the base of the ischium, while the pubic bones were separated from each other in front. The bones of the hind limb are altogether shorter in the German fossil than in Dimorphodon, especially in the tibia; but the structure of the metatarsus is just the same, even to the short fifth metatarsal with its two digits, only those bones are extremely short, instead of being elongated as in Dimorphodon. It is therefore convenient, from the different proportions of the body, that Campylognathus may be separated from Dimorphodon; but so much as is preserved of the English specimen from the Upper Lias of Whitby rather favours the belief that our species should also be referred to Campylognathus, which had not been figured when the Whitby skull was referred to Scaphognathus by Mr. Newton. It may be doubtful whether there is sufficient evidence to establish the distinctness of the other German genus Dorygnathus, though it may be retained pending further knowledge.

In these characters are grounds for placing the Lias Pterodactyles in a distinct family, the Dimorphodontidae, as was suggested in 1870. This evidence is found in the five metatarsal bones, of which four are in close contact, the middle two being slightly the longest, so as to present the general aspect of the corresponding bones in a Mammal rather than a Bird. Secondly, the very slender fibula, prolonged down the length of the shin bone, which ends in a rounded pulley like the corresponding bone of a Bird. Thirdly, the great elongation of the third wing phalange. Fourthly, the prolongation of the coracoid bone beyond the articulation for the humerus, as in a Bird. And the toothless, spear-shaped beak, and jaw with large teeth in front and small teeth behind, are also distinctive characters.