Order I. PSEUDOSUCHIA.
The few members of this peculiar group of reptiles are all restricted to the Keuper or variegated marls, although they seem to have had a wide distribution, some having been found in Germany, others in New Mexico. They perhaps form an early side-branch of the generalised Crocodilian stock, which died out with the Jurassic age.
The skull is distinctly short and pointed. The premaxillaries are very small and are dorsally separated from each other by the large nasals, which also keep the maxillae widely asunder. The nostrils are latero-terminal, bordered chiefly by the nasals, below by the premaxillae and part of the maxillae. The orbit is bordered below by the strong jugals, in front by the prefrontal, above by a supra-orbital and a small postfrontal, behind by a postorbital, which, firmly connected with the jugal and squamosal, shuts off a supratemporal foramen. There is also a lateral temporal fossa, and a large hole enclosed by the lacrymal and the maxillary bones. The teeth are restricted to the anterior half of the jaws. The neck, back, and tail are covered by two rows of large and broad, closely-jointed bony plates; smaller plates protect the sides and the ventral surface. The vertebrae are still unknown.
Aëtosaurus ferratus of the Upper Keuper near Stuttgart is the best known. One of the greatest treasures of the Stuttgart Museum is a slab of sandstone, about 2 square yards in size, upon which lie huddled together twenty-four individuals of various sizes, the largest measuring 86 cm. or 2 feet 10 inches. They are in a beautiful state of preservation, and many of them are in the most life-like attitudes, just as if a mass of sand had fallen upon them and crushed them down, and as if they were struggling to get out.
Erpetosuchus and Ornithosuchus of the Elgin sandstone seem to be allied forms.
Order II. PARASUCHIA.
As the name implies, a collateral branch of the true Crocodilia. They are, like the Pseudosuchia, restricted to the Keuper formation. The vertebrae are mostly biconcave, sometimes with nearly plain, scarcely concave, central joints. The premaxillae are very long and powerful. The nostrils lie far back, rather near the orbits, on the top of the snout, within the anterior half of each nasal and almost above the choanae. The latter are situated in front of the palatine bones and are divided by a backwardly directed process of the vomer, which is plainly visible on the roof of the mouth. The palatines and pterygoids leave a wide median space between them. The pterygoids are narrow and have three processes, the antero-lateral of which joins the palatines and the maxillary bones (there being no separate ectopterygoid), the inner joins the basi-occipital, and the postero-lateral the quadrate.
The orbit is surrounded by the frontal, prefrontal, lacrymal, postorbital and postfrontal, while the strong jugal is excluded. The temporal region shows a lateral and a dorsal foramen; the latter opens backwards and above the occiput, being bordered in front by the parietal, laterally by the squamoso-occipital bridge.
The vertebrae are amphicoelous. The first and second vertebrae are devoid of ribs; the cervicals and first thoracics carry separate capitular and tubercular processes for the attachment of the ribs, while the ribs of the rest of the trunk are carried entirely by the long diapophyses, as in the modern Crocodiles. The dermal armour consists of two rows of broad, dorsal, and several rows of smaller, lateral, bony plates.
Belodon is by far the best-known genus, with several species in South Germany and North America, some of which reached a length of 10 feet, without ventral armour. The closely allied Stagonolepis of the Elgin sandstone in Scotland had dorsal and ventral armour. Other genera in the Triassic formations of India and North America.