Dragons of the Air Part 9

As the Kingfisher finds its food (see Fig. 20) from the surface of the water without being in the common sense of the term a water bird, so some Pterodactyles may have fed on fish, for which their teeth are well adapted, both in the stream and by the sh.o.r.e.

A Pterodactyle's teeth vary a good deal in appearance. The few large teeth in the front of the jaw in Dimorphodon, a.s.sociated with the many small vertical teeth placed further backward, suggest that the taking of food may have been a process requiring leisure, since the hinder teeth adapted to mincing the animal's meat are extremely small. The way in which the teeth are shaped and arranged differs with the genera. In Pterodactylus they are short and broad and few, placed for the most part towards the front of the jaws. Their lancet-shaped form indicates a shear-like action adapted to dividing flesh. In the a.s.sociated genus Rhamphorhynchus the teeth are absent from the extremity of the jaw, are slender, pointed, s.p.a.ced far apart, and extend far backward. When the jaws of the Rhamphorhynchus are brought together there is always a gap between them in front, which has led to belief that the teeth were replaced by some kind of h.o.r.n.y armature which has perished. In the long-nosed English type of Ornithocheirus the jaws are compressed together, so that the teeth of the opposite sides are parallel to each other, with the margins well filled with teeth, which are never in close contact, though occasionally closer and larger in front, in some of the forms with thick truncated snouts.

It is not the least interesting circ.u.mstance of the dent.i.tion of Pterodactyles that, a.s.sociated in the same deposits with these most recent genera with teeth powerfully developed, there is a genus named Ornithostoma from the resemblance of its mouth to that of a bird in being entirely devoid of teeth. It is scarcely possible to distinguish the remains of the toothed and toothless skeletons except in the dentary character of the jaws. There is no evidence that the toothless types ever possessed a tooth of any sort. They were first found in fragments in England in the Cambridge Greensand, but were afterwards met with in great abundance in the Chalk of Kansas, where the same animals were named Pteranodon. A jaw so entirely bird-like suggests that the digestive organs of Pterodactyles may in such toothless forms at least have been characterised by a gizzard, which is so distinctive of Birds.

The absence of teeth in the Great Ant-eater and some other allied Mammals has transferred the function which teeth usually perform to the stomach, one part of which becomes greatly thickened and muscular, adapting itself to the work which it has to perform. It is probable that the gizzard may be developed in relation to the necessities which food creates, since even Trout, feeding on the sh.e.l.l-fish in some Irish lochs, acquire such a thickened muscular stomach, and a like modification is recorded in other fishes as produced by food.

Closely connected with an animal's habits is the protection to the body which is afforded by the skin. In Pterodactyles the evidence of the condition of the skin is scanty, and mostly negative. Sometimes the dense, smooth texture of the jaw bones indicates a covering like the skin of a Lizard or the hinder part of the jaw of a Bird. Some jaws from the Cambridge Greensand have the bone channeled over its surface by minute blood vessels which have impressed themselves into the bone more easily than into its covering. Thus in the species of Ornithocheirus distinguished as _microdon_ the palate is absolutely smooth, while in the species named _machaerorhynchus_ it is marked by parallel impressed vascular grooves which diverge from the median line. This condition clearly indicates a difference in the covering of the bone, and that in the latter species the covering had fewer blood vessels and more h.o.r.n.y protection than in the other. The tissue may not have been of firmer consistence than in the palate of Mammals. The extremity of the beak is often as full of blood vessels as the jaw of a Turtle or Crocodile.

COVERING OF THE BODY

There is no trace even in specimens from the Solenhofen or Stonesfield Slate of any covering to the body. There are no specimens preserved like mummies, and although the substance of the wings is found there is no trace of fur or feathers, bones, or scales on the skin. The only example in which there is even an appearance suggesting feathers is in the beautiful Scaphognathus at Bonn, and upon portions of the wing membrane of that specimen are preserved a very few small short and apparently tubular bodies, which have a suggestive resemblance to the quills of small undeveloped feathers. Such evidences have been diligently sought for. Professor Marsh, after examining the wing membranes of his specimen of Rhamphorhynchus from Solenhofen, stated that the wings were partially folded and naturally contracted into folds, and that the surface of the tissue is marked by delicate striae, which might easily be taken at first sight for a thin coating of hair. Closer investigation proved the markings to be minute wrinkles on the under surface of the wing membrane. This negative evidence has considerable value, because the Solenhofen Slate has preserved in the two known examples of the bird Archaeopteryx beautiful details of the structure of the larger feathers concerned in flight. It has preserved many structures far more delicate.

There is, therefore, reason for believing that if the skin had possessed any covering like one of those found in existing vertebrate animals, it could scarcely have escaped detection in the numerous undisturbed skeletons of Pterodactyles which have been examined.

The absence of a recognisable covering to the skin in a fossil state cannot be accepted as conclusive evidence of the temperature, habits, or affinities of the animal. Although Mammalia are almost entirely clothed with dense hair, which has never been found in a recognisable condition in a fossil state in any specimen of Tertiary age, one entire order, the Cetacea, show in the smooth hairless skins of Whales and Porpoises that the cla.s.s may part with the typical characteristic covering without loss of temperature and without intelligible cause. That the absence of hair is not due to the aquatic conditions of rivers or sea is proved by other marine Mammals, like Seals, having the skin clothed with a dense growth of hair, which is not surpa.s.sed in any other order. The fineness of the growth of hair in Man gives a superficial appearance of the skin being imperfectly clothed, and a similar skin in a fossil state might give the impression that it was devoid of hair. There are many Mammals in which the skin is scantily clothed with hair as the animal grows old. Neither the Elephant nor the Armadillo in a fossil state would be likely to have the hair preserved, for the growth is thin on the bony s.h.i.+elds of the living Armadilloes. Yet the difficulty need be no more inherent in the nature of hair than in that of feathers, since the hair of the Mammoth and Rhinoceros has been completely preserved upon their skins in the tundras of Siberia, densely clothing the body. This may go to show that the Pterodactyle possessed a thin covering of hair, or, more probably, that hair was absent. Since Reptiles are equally variable in the clothing of the skin with bony or h.o.r.n.y plates, and in sometimes having no such protection, it may not appear singular that the skin in Ornithosaurs has. .h.i.therto given no evidence of a covering. From a.n.a.logy a covering might have been expected; feathers of Birds and hair of Mammals are non-conducting coverings suited to arrest the loss of heat.

With the evidence, such as it is, of resemblance of Ornithosaurs to Birds in some features of respiration and flight, a covering to the skin might have been expected. Yet the covering may not be necessary to a high temperature of the blood. Since Dr. John Davy made his observations it has been known that the temperature of the Tunny, above 90 Fahrenheit, is as warm as the African scaly ant-eater named the Pangolin, which has the body more amply protected by its covering. This ill.u.s.tration also shows that hot blood may be produced without a four-celled heart, with which it is usually a.s.sociated, and that even if the skin in Pterodactyles was absolutely naked an active life and an abundant supply of blood could have given the animal a high temperature.

The circ.u.mstance that in several individuals the substance of the wing membrane is preserved would appear to indicate either that it was exceptionally stout when there would have been small chance of resisting decomposition, or that its preservation is due to a covering which once existed of fur or down or other clothing substance, which has proved more durable than the skin itself.

[Ill.u.s.tration: FIG. 48. REMAINS OF DIMORPHODON FROM THE LIAS OF LYME REGIS

SHOWING THE SKULL, NECK, BACK AND SOME OF THE LONGER BONES OF THE SKELETON

_From a slab in the British Museum (Natural History)_]

CHAPTER XIII

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.

[Ill.u.s.tration: FIG. 49. LEFT SIDE OF DIMORPHODON (RESTORED) AT REST]

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 princ.i.p.al 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.

[Ill.u.s.tration: FIG. 50. DIMORPHODON MACRONYX RESTORED FORM OF THE ANIMAL]

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 _Ill.u.s.trated 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.

[Ill.u.s.tration: FIG. 51. DIMORPHODON MACRONYX WALKING AS A QUADRUPED RESTORATION OF THE SKELETON]

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 princ.i.p.al 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.

[Ill.u.s.tration: FIG. 52. DIMORPHODON MACRONYX WALKING AS A BIPED _Based chiefly on remains in the British Museum_]

[Ill.u.s.tration: FIG. 53. LOWER JAW OF DORYGNATHUS SEEN FROM BELOW

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.

[Ill.u.s.tration: FIG. 54. DIMORPHODON MACRONYX SHOWING THE MAXIMUM SPREAD OF THE WING MEMBRANES]

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.

[Ill.u.s.tration: FIG. 55. THE LEFT SIDE OF THE PELVIS OF DIMORPHODON SHOWING THE TWO PREPUBIC BONES]

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 s.h.i.+n 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.

CHAPTER XIV

ORNITHOSAURS FROM THE MIDDLE SECONDARY ROCKS

RHAMPHOCEPHALUS

THE Stonesfield Slate in England, which corresponds in age with the lower part of the Great or Bath Oolite, yields many evidences of terrestrial life--land plants, insects, and mammals--preserved in a marine deposit. A number of isolated bones have been found of Pterodactyles, some of them indicating animals of considerable size and strength. The nature of the limestone was unfavourable to the preservation of soft wing membranes, or even to the bones remaining in natural a.s.sociation. Very little is known of the head of Rhamphocephalus. One imperfect specimen shows a long temporal region which is wide, and a very narrow inters.p.a.ce between the orbits; with a long face, indicated by the extension of narrow nasal bones. The lower jaw has an edentulous beak or spear in front, which is compressed from side to side in the manner of the Lia.s.sic forms, but turned upward slightly, as in Dorygnathus or Campylognathus. Behind this extremity are sharp, tall teeth, few in number, which somewhat diminish in size as they extend backward, and do not suddenly change to smaller series, as in the Lias genera. A few small vertebrae have been found, indicating the neck and back. The sacrum consists of five vertebrae. One small example has a length of only an inch. It is a little narrower behind than in front, and would be consistent with the animal having had a long tail, which I believe to have been present, although I have not seen any caudal vertebrae. The early ribs are like the early ribs of a Crocodile or Bird in the well-marked double articulation. The later ribs appear to have but one head. #V#-shaped abdominal ribs are preserved. Much of the animal is unknown. The coracoid seems to have been directed forward, and, as in a bird, it is 2-1/2 inches long. The humerus is 3-1/2 inches long, and the fore-arm measured 6 inches, so that it was relatively longer than in Dimorphodon. The metacarpus is 1-3/4 inches long. The wing finger was exceptionally long and strong. Professor Huxley gave its length at 29 inches. My own studies lead to the conclusion that the first finger bone of the wing was the shorter, and that although they did not differ greatly in length, the second was probably the longest, as in Campylognathus.

Professor Huxley makes the second and third phalanges 7-3/4 inches long, and the first only about 3/8 inch shorter, while the fourth phalange is 6-1/2 inches. These measurements are based upon some specimens in the Oxford University Museum. There is only one first phalange which has a length of 7-3/4 inches. The others are between 5 and 6 inches, or but little exceed 4 inches; so that as all the fourth phalanges which are known have a length of 6-1/2 inches, it is possible that the normal length of the first phalange in the larger species was 5-1/2 inches. The largest of the phalanges which may be cla.s.sed as second or third is 8-1/2 inches, and that, I suppose, may have been a.s.sociated with the 7-3/4 inches first phalange. But the other bones which could have had this position all measure 5-1/2 and 7-3/4 inches. The three species indicated by finger bones may have had the measurements:--