septomaxilla 

 nasal 



parietal postorbital suprotemporal 



frontal _\ ' 



postparietal 



anterior palatine fenestra 



nterpterygoid fenestra 



parasphenoid 

 hypophyseal fenestrajO 



postorbital 

 parietal foramen /q 



supra- 

 temporal 



B 



postparietals 



tabular 



notochord canal 



in otoccipital division of endocronium 



Figure 4-25. Skull and mandible of khthyoslega. A, lateral view; B, dorsal viev* of skull; C, palatal 

 view of skull. (After Jarvik, 1952, Sdve-Soderbergh, 1932) 



The eosuchians are known from the Upper Permian. The 

 most primitive members belong to the Family Millerettidae, 

 which has been raised to a separate order by some. In the 

 millerettids the shield was basically anapsid, postparietals 

 were still paired but lay on the occipital aspect, the inter- 

 temporal was lacking but the supratemporal and tabular 

 were present. The posterolateral margin of the skull was 

 slightly notched, as for a tympanic membrane (an amphibian 

 feature). In some species the cheek had a small chink in it 

 between jugal and squamosal (a synapsid opening). The 

 palate was captorhinomorph-like, but the parasphenoid 



rostrum was toothed and the ectopterygoids were small. 

 Petrolacosaurus agreed in all known details with this descrip- 

 tion. 



Synapsid reptiles, the pelycosaurs, were common in the 

 early Permian and are known also from the uppermost 

 Pennsylvanian. Since the group is quite well defined and 

 frequently highly specialized in form when first encoun- 

 tered, it is probable that its ancestors were contemporaries of 

 Petrolacosaurus or occurred even earlier in time. It is quite 

 probable that, since the pelycosaurs retain both supratem- 

 poral and tabular bones in the cranial roof along with 



OTHER TETRAPODS • 89 



