Their ancestors are the Microsauri, whilst they themselves seem to be very near the root whence have sprung most, if not all, other main branches of the reptiles, notably Crocodilia, Dinosauria, and Sauria. In fact the Prosauri, although apparently few in number, seem to represent the central stem of the reptilian tree. Only one of them is still surviving, the famous Sphenodon, now represented by a single species in New Zealand.
Sub-Order 1. Protorosauri.–The ventral half of the pelvis seems to have formed one broad, continuous mass of cartilage in which the pubic bones are represented by a pair of oval, rather disc-shaped ossifications, while the ischia are more elongated. The pelvis consequently still bears a great resemblance to that of the Microsauri, and thereby also to the Stegocephalous condition, but the ilium seems to be attached to more than two vertebrae. The vertebrae are deeply biconcave, perhaps even with a persistent continuous chorda. The neural arches bear high, laterally compressed spines, but no diapophysial or lateral processes, the ribs being placed mostly intervertebrally and having lost their tubercular portions. The ribs are continued to about the sixth caudal vertebra. Intercentral wedges exist in an unbroken series between all the vertebrae from the atlas to the tail, where they are represented by movable chevrons. A costal sternum seems to be absent, unless it was quite cartilaginous. The shoulder-girdle is complete, consisting of a long interclavicle, clavicles, disc-shaped coracoids, and scapulae; but there are no cleithra, and no indication of precoracoids or even notches in the coracoids. The fore- and hind-limbs are complete and primitive, with five digits. The abdomen is protected by numerous oat-shaped little ossifications, which are arranged in many transverse or rather chevron-shaped rows, still greatly resembling the condition prevailing in the Microsauri, except that they have sunk deeper into the skin, being no longer directly covered by the scales. The skull, being no longer completely encased by bones, and possessing now wide supra- and infra-temporal fossae, appears at first sight much like that of a generalised lizard, except that it possesses three very conspicuous and distinct arcades in the temporal region: namely, the orbito-squamosal bridge across the temporal fossa, formed by the postorbital and squamosal; the arch formed by the squamosal with the postero-lateral buttress of the parietal; and the infratemporal arch or jugal bridge. The jugal itself is long, connecting the quadrato-jugal with the maxillary and lacrymal, and sending up an ascending process to the postorbital bone, thus taking a considerable share in the formation of the orbit. The quadrato-jugal is small, apparently fused with the quadrate, which itself is firmly overlaid by the squamosal. The quadrates are further fixed by being buttressed by the pterygoids, which rest upon short basisphenoid processes and extend far forwards, meeting the vomers and separating the palatines. The premaxillae are short, the nares small and terminal, the nasal bones are large. There is a small interparietal foramen. The teeth are acrodont and pointed, forming unbroken series on the premaxillaries, maxillaries, palatines and dentaries, and there are scattered little teeth on the vomers.
Palaeohatteria longicaudata from the Lower Red Sandstone of Saxony. Total length about 18 inches, with six cervical, twenty trunk, three or four sacral, and about fifty caudal vertebrae. The teeth are ankylosed with the supporting bones. The five fingers have 2, 3, 4, 5, 3 phalanges respectively. For the skull see Fig. 54, G, p. [280]. Telerpeton elginense from the Triassic sandstone of Scotland, and perhaps Saurosternon of the South African Karroo sandstone seem to be allied.
Protorosaurus (πρῶτος = first, ὤρα = spring, or dawn, not Proterosaurus) apparently several species, e.g. P. lincki in the Upper Permian (marl-slate and magnesian limestone) of Thuringia and Durham. About 4 or 5 feet long, and in its general appearance rather like a Monitor-lizard, with about eight cervical vertebrae, most of which carry slender backwardly-pointing ribs, sixteen long-ribbed trunk-vertebrae, followed by three or four sacrals and more than thirty caudals, some of which have bifurcated spinous processes.
Sub-Order 2. Rhynchocephali.–The ventral pelvic bones resemble those of lizards and enclose a wide pubo-ischiadic foramen. There are only two sacral vertebrae. The abdominal ribs are closely packed, each transverse set consisting of only three rod-shaped pieces instead of many small oat-shaped nodules. The intercentra are sometimes suppressed in the trunk-region.
Rhynchosaurus from the Upper Trias of Warwickshire and Shropshire, and Hyperodapedon of the same age, found at Elgin, in Warwickshire, and also in Central India, are rather large, H. gordoni measuring 6 feet in length. Both have a short, broad, and stout cranium, and curved down, toothless premaxillae, hence the name Rhynchocephali; the nares are confluent; the teeth are numerous and small, and are liable to be worn down so that the animals ultimately bite with the edges of the jaws, to which the teeth are ankylosed. The premaxillaries of Rhynchosaurus are curved downwards over a slightly upcurved, likewise toothless process of the mandibles, which form a strong symphysis. All the teeth are very small, absent, or minute on the mandibles, forming one series on the maxillae, several rows on the vomers and especially on the palatines, which latter remain separated from each other. Hyperodapedon seems to have lost the intercentra; its vertebrae are solid, those of the neck are opisthocoelous. The interparietal foramen is likewise abolished. The hook-shaped end of the curved-down premaxillae fits into a bifurcation of the mandibles in front of their stout symphysis. The teeth are similar to those of the other genus. Whilst these, the earliest known genera of Rhynchocephali, are already in various ways rather specialised, e.g. the hooked beak and the loss of the intercentra, the two following fossil genera, although of much later date, namely Upper Triassic, are more closely allied to the recent Sphenodon.
Homoeosaurus pulchellus and other species in Germany are only 6 to 8 inches long. The vertebral column consists of twenty-three presacral and many caudal vertebrae. The first five cervicals are devoid of ribs. Intercentra are restricted to the neck and the anterior portion of the tail. The mandibles are not fused together. The nares are divided by a bony septum. Each premaxillary has one rather broad tooth.
Fig. 58.–Sphenodon punctatum. × ⅓.
The teeth of the maxillaries and mandibles are triangular, much worn down in front. The ribs are devoid of uncinate processes. Closely allied but larger is Sauranodon of France, which has lost the upper teeth and uses the sharp margins of the jaws instead.