The occipital condyle of C. platyceps is kidney-shaped, with the concavity directed upwards; in C. berryi it is separated into two distinct knobs, the middle, basioccipital portion being apparently wanting. The mandible possesses a long coronoid process which ascends obliquely into the temporal fossa.
Aelurosaurus, Lycosaurus, Galesaurus, and many others, likewise of the Karroo formation. In the first genus the splenial bones help to form the symphysis of the lower jaw; teeth are also found on the palate, in opposition to Lycosaurus. This has a skull 6 inches in length; the dental formula on either side is i. 4/3, c. 1/1, m. 5/5; the molars are slender, conical, and recurved. Galesaurus seems to have been rather small, the low, triangular skull measuring only 2 to 3 inches in length, with four or five sharply pointed incisors, prominent canines and four or five small multicuspid or deeply serrated little molars.
Endothiodon, with several species from the Karroo formation, is of uncertain systematic position, only imperfect skulls being known. The animals must have been large and bulky, the skulls being very massive and at least one foot in length. The premaxillaries and the maxillaries are toothless, their alveolar borders forming cutting, prominent edges. The same applies to the very strong lower jaw; but there is a pair of tooth-like stout projections in the upper and lower jaws in the place of canine teeth. True, enamelled, small, apparently conical or low and perhaps blunt teeth occur on either side in one or three longitudinal series upon the palate, and in corresponding positions on the inner sides of the two halves of the lower jaw. It is doubtful if the upper teeth are carried by the palatines or by the broadened inner flanges of the maxillaries. The choanae seem to lie between the pterygoids and the palatines, incompletely roofed in by ventral extensions of the latter towards the middle line.
Direct affinity of Endothiodon (ἐνδοθί, within) with Placodus is unlikely; the same applies to the Dicynodontia, although the restriction of the teeth to the palate seems to point as much to the former genus as do the toothless cutting edges of the jaws to the forms like Oudenodon.
Other Theriodont reptiles have been described from the upper Permian of Russia, for instance Deuterosaurus and Brithopus, but the determination rests upon insufficient fragments. North America has yielded many strange Theromorphous fossils, some of which may belong to the Theriodont order, while others seem to be intermediate between this and the other orders. Diadectes of Texas, for instance, seems to be a Theriodont creature; while in Empedias molaris, with a skull about 8 inches in length, the teeth form an uninterrupted series without distinct canine tusks, and the incisors are distinguished from the molars only by the transversely broadened shape of the latter. Very small teeth are arranged along the median line of the vomer and united palatine bones. In Clepsydrops, Dimetrodon, and Naosaurus of Texas the teeth are differentiated into incisors, canines, and molars, although not so regularly as in the typical Theriodont forms described above, one or more pairs of teeth being enlarged into canine-like tusks. In the latter two genera the spinous processes of the thoracic vertebrae are enormously elongated, standing up vertically to a height of 2 feet, while the centra of the vertebrae measure only one inch in diameter. In Naosaurus claviger these upright spines carry on either side half a dozen transverse projections. Stereorhachis of the Permian of France is typically Theriodont in the structure of its shoulder-girdle, humerus, and pelvis, but the dentition is composed of 3/3 incisors, no canines, and 6/10 pointed molars.
The following genera have been placed by Seeley in the family Gomphognathidae. Microgomphodon, with broader and less prominently multicuspid teeth than those of the typical Theriodonts, seems to lead to Gomphognathus, which has the following dentition: i. 3/3, c. 1/1, m. 12/12, with a long diastema between the canines and molars, some of which latter are nearly as broad as they are long, and have comparatively low tubercles on the crowns. The skull is remarkably like that of a Carnivorous Mammal. There are incisive foramina behind the premaxilla. The maxillaries and palatines form a united palatal roof, and behind them open the choanae. The occipital condyle is kidney-shaped. The mandible is most extraordinary, approaching that of the Mammalian, especially the Marsupial type, except that it is still composed of several pieces. The articular facet for the mandible is borne by an outward or lateral projection, while the bulk of the posterior half of the jaw projects inwards like a broad flange, undoubtedly recalling the so-called inner inverted angle of the Marsupial jaw. The coronoid process is large and extends far into the temporal fossa. Nearly the whole skeleton of Microgomphodon is known; the lumbar ribs are broadened and overlap as in Cynognathus, and the mandible is typically compound, so that there is no doubt about the affinities of this genus with the Theriodontia. It throws light upon Gomphognathus and the three likewise South African genera Diademodon, Trirachiodon and Tritylodon, which are all known from imperfect skulls only. Their teeth are restricted to the jaws, the molars have flat, multitubercular crowns and bear an extraordinary resemblance to those of Mammals. Some of the molars of Tritylodon are said even to possess two roots, but this point, absolutely unique in Reptiles, but common in Mammals, is not certain. The few upper incisors of Tritylodon are rather large, chisel-shaped, and extend like those of the Rodent-type back into the maxillaries; canines are absent, leaving a diastema. Trirachiodon has prominent canines, the five upper molars are multitubercular, rather flat, and much broader transversely than in the longitudinal direction. Still, even these creatures, with skulls of the size of that of a small fox, possessed distinct prefrontal and postfrontal bones, and are, at least in this respect, typical Reptiles.
Order III. ANOMODONTIA.
The cranium is not roofed in. The pedicle for the suspension of the lower jaw is much elongated, slants slightly forwards, and is composed of the long quadrate, which is laterally overgrown by the squamosal bone. The teeth are restricted to a pair of strong, tusk-like canines, or they are altogether absent. The margins of the upper and especially those of the lower jaw are trenchant, and were possibly furnished with a thick horny armature like those of tortoises.
Dicynodon, with many species from the Karroo formation of South Africa, reached formidable dimensions. The thick, curved skull is in size and outline not unlike that of a large lion, hence D. leoniceps, D. tigriceps, etc. The zygomatic arch is almost mammalian, except that the posterior boundary of the orbit is formed by a distinct postfrontal bone. The nostrils are lateral. The canine tusks (Fig. 54, E, p. [280]) are very large. The choanae open behind the rhomboid vomer and between the separated palatine bones, which are posteriorly confluent with the medially united pterygoids. The latter send out flat extensions, along the lateral side of the palatines; these extensions reach the maxillaries and probably represent the ectopterygoids. The occipital condyle is distinctly triple, being equally composed of the basi- and latero-occipital bones.
The three bones of the shoulder-girdle meet at the glenoid fossa; the scapula has the indication of a spine. The pelvis is stout, attached to four or five vertebrae, converting the latter into a very Mammalian-like sacrum, the position of which lies distinctly in front of the acetabulum. The latter is closed, composed by the three pelvic bones. The pubes and ischia are fused together, leaving only a very small obturator-foramen. The limbs are plantigrade and pentadactyle, very stout; the humerus and femur have enormous crests.