184 



REPTILIA 



CLASS III 



This family is regarded by Seeley as typical of a distinct order of reptiles, 

 Gomphodontia, and ancestral to mammals. 



Tritylodon, Owen (Fig. 288). Known by small, decidedly mammalian-like 



crania. Karoo 

 Formation; South 

 Africa. 



Gomphognathus, 

 Diademodon, Mi- 

 crogomphodon, Tri- 

 rachodon, Seeley. 

 The first -named 

 has a double 

 occipital condyle, 



Fig. 288. 



Tritylodon longaevus, Owen. Trias; Taba-chow, Basutoland, South Africa. 

 Skull from superior and palatal aspects, 2/ 3 (after Owen). 



Fig. 289. 



THglyplius fraasi, 

 Lyd. Upper Trias : 

 Hohenheim, Wurtem- 

 berg. Upper molar, 

 1/1 and 2/j (after Fraas). 



and its single zygomatic arch resembles that of mammals. Theriodesmus, 

 Seeley, is known by a remarkably mammalian-like fore-limb and manus. 

 Karoo Formation ; South Africa. 



Triglyphus, Fraas (Fig. 289). Known only by minute teeth from the Upper 

 Triassic Bone-bed of Hohenheim, near Stuttgart. 



Sub-Order 3. ANOMODONTIA. Owen. (Dicynodontia, Owen.) 



Investing bones of temporal region contracting into a single broad arcade, formed 

 principally by the enormously developed squamosal. External bones not sculptured ; 

 supratemporal vacuity large; quadrate small; premaxillae fused; external nares 

 separated. Jaws edentulous, or with a single pair of tusk-like teeth in the maxillae 

 set in deep alveoli and growing from persistent pidps. Cervical ribs double-headed, 

 dorsal single-headed. Sacrum of five or six vertebrae. 



The Anomodonts or Dicynodonts are mostly large terrestrial reptiles of 

 Triassic age, of which no complete skeletons have yet been discovered, but 

 numerous crania, vertebrae, and other fragments are known from South Africa, 

 East India, Ural, and Scotland. 



The vertebral column consists of seven or eight cervical, twelve or thirteen 

 dorsal, five or six sacral, and about twenty caudal vertebrae. The centra are 

 short and slightly amphicoelous. Double-headed ribs are borne by the cervical, 

 and single-headed ribs by the dorsal vertebrae. The cranial sutures (Fig. 290) 

 are frequently obscure and difficult to determine. The brain cavity is very 

 small and the surfaces for attachment of the muscles of the jaw unusually 

 large. On either side of the upright occiput is an enormously developed 

 squamosal, which forms the greater part of the single temporal arcade, and is 



