EARLIEST REPTILES 



187 



LABIDOSAURUS 





PERMO- 

 CARBONIFEROUS 



,5355?-^,X n 



the primitive ancestors from which the various orders of reptiles 

 descended belong to a single, a double, or a multiple stock. 



Passing to the widely different amphibian-like order known 

 as cotylosaurs, we see animals ^-r*^-F)7^\ 

 which, on the one hand, grade ^^^^^^'^j-^^' 

 into the more fully aquatic, pad- 

 dle-footed, free-swimming Lim- 

 noscelis with a short, crocodile- 

 like head, which propelled itself 

 by means of its long tail, and, 

 on the other hand, there devel- 

 oped short-tailed, semi-acjuatic 

 forms, such as the Lahido- 

 saurus. In adaptation to the 

 more purely terrestrial habitats 

 there is sometimes a reduction 

 in the length of the tail and 

 greater perfection in the struc- 

 ture of the limbs and the various 

 forms of armature. In Pantyliis 

 these defenses appear in the 

 form of bony ossicles of the skin 

 and scutes; in Chilonyx the 

 skull top is covered with tuber- 

 culated defenses; in the slow- 

 moving Diadedes the body is 

 partly armored, the animal be- 

 ing proportioned like the exist- 

 ing Gila monster and probably 

 of nocturnal habits, which is in- 

 ferred from the large size of the 

 eyes. 



i3 



Fig. 67. Reptiles with Skulls Trans- 

 itional IN Structitre from the 

 Amphibian Skull. 



Typical solid-headed reptiles (Coty- 

 losaurs) characteristic of Permo-Car- 

 boniferous time in northern Texas, 

 including the three forms Seynioiiria, 

 Labidosaiints, and the powerful Dia- 

 dedes, which resembles the existing 

 Gila monster. The head in the mounted 

 skeleton of Diadcctcs (lower) in the 

 American Museum of Natural History 

 is probably bent too sharply on the 

 neck. Restorations for the author by 

 W. K. Gregory and Richard Deckert. 

 Labidosaiirus and Seymouria chiefly 

 after Williston. 



