The lacertian affinities of the Telerpeton are well marked in the relative size and form of the bones of its extremities, the situation of its pelvis, and probably in the articulation and the length of its ribs; but the contracted, biconcave centrum, and the short neural spine of the vertebræ, as well as the horizontality of the articulating surfaces of the zygapophyses, and the general uniformity of character throughout the spinal column, are to be regarded as batrachian modifications. Probably the original was a peculiar type, which, in the present state of our knowledge, it would be rash to ascribe to either order. The length of the original animal could not have exceeded six or seven inches. [Lign. 236] represents in outline the probable form of this small, but most interesting reptile.
V. Pterosaurians, or Flying Reptiles.—Pterodactylus (wing-fingered reptile). [Lign. 237]. Petrif. p. 187; Wond. p. 577; Bd. pl. xxi. xxii.—The extinct reptiles denominated Pterodactyles, constituting a few genera of an order of Saurians organized for aërial life,[674] are unquestionably the most marvellous even of the wonderful beings which the relics of the Age of Reptiles have enabled the palæontologist to reconstruct. With a long-snouted head and long neck, much resembling that of a bird, bat-like wings, and a small trunk and tail, with lacertian affinities in its skull, teeth, and skeleton, and with a bird-like structure of sternum and scapular arch, these creatures present an anomaly of structure as unlike their fossil contemporaries, as is the duck-billed Ornithorhynchus, of Australia, to existing animals. The cranium, or brain-case, is small; the jaws are either long, and armed with numerous sharp-pointed teeth, or toothless, like those of a bird. The teeth of the Pterodactyle are all laniary; they are simple, of a conical form, recurved, with but little difference in their form and size, and implanted in distinct sockets, with wide intervals between each. In some species there are twenty-eight or thirty in the lower, and twenty-two in the upper jaw.
[674] The only known recent reptile at all analogous is the little Draco volans of the East Indian Islands; but even this can scarcely be regarded as a flying animal, its lateral membranous expansions, which are rather parachutes than wings, and formed by elongated ribs, not by the fingers, presenting but a rudimentary condition of wings compared with those of the Bat and the Pterodactyle.
The orbit is very large; the sclerotica consists of an annular row of bony plates, but less in number than in the Ichthyosaurus; the external orifice of the nostrils is near the orbits; remains of the os hyoides (bone of the tongue) have been observed.
Lign. 237. Pterodactylus crassirostris: 1/2 nat. size.
Oolite. Solenhofen.
The cervical vertebræ are large and strong, and capable of great flexibility forwards and backwards, probably to allow the head to fall back to the centre of gravity during flight. There are frequently traces of ossified condition of the tendons of the muscles of the neck. This is well seen in P. macronyx and P. crassirostris ([Lign. 237]), and is a peculiarity dependent on the additional support required by the long neck of the animal.
The dorsal vertebræ are from seventeen to twenty in number. The sacrum is formed by the coalescence of two vertebræ only, as in existing reptiles, and not of many, as in birds and certain extinct saurians. The tail is generally short, an unusual character with saurians; but a species with a long tail occurs at Solenhofen.
There are five toes or digits on each foot; the outer finger of the fore-arm is immensely elongated, for the support of a membranous expansion (the impression of this wing-membrane is preserved on the stone in some examples); and the other digits, of fore and hind feet, terminated in long curved claws. The size and form of the extremities show that the Pterodactylus was capable of perching on trees, of hanging against perpendicular surfaces, and of standing firmly on the ground, when, with its wings folded, it might crawl on all-fours, and walk or hop like a bird. A reference to the graphic description of the characters and probable habits of these beings, by Dr. Buckland, Bd. i. p. 221, and the beautiful illustrations accompanying it (Bd. ii. pl. xxi. xxii.), will equally instruct and gratify the reader.