490 



HISTORICAL GEOLOGY 



Fig. 465. — The head of a Permian 

 reptile, Labidosaurus. 



usually long tails (Fig. 461). Some had long, sharp, curved teeth 

 (Labidosaurus, Fig. 465) arranged in two or more rows, which were 

 probably used for prodding in the mud for soft-bodied invertebrates, 

 and for crushing; some had conical teeth in front and crushing teeth 

 behind ; and some had a mouth filled everywhere on jaws and palate 



with short, stumpy teeth, suitable 

 only for crushing shellfish ; while 

 others had slender teeth indicat- 

 ing insectivorous habits. In some, 

 the claws terminated in flattened 

 nails, while in others the claws 

 were sharp and curved. The 

 habits of this group varied some- 

 what, some being more terrestrial than others, but all probably 

 lived in swampy places and about lagoons. 



A second group of Carboniferous reptiles (pelycosaurs) had lighter 

 skulls than those of the first group ; larger necks ; longer, better- 

 formed legs and feet, and usually longer tails. The best known of 

 these (Dimetrodon, Fig. 466) was about 10 feet in length and was 

 especially characterized by a finlike crest on the back formed by 

 spines of its vertebrae. The skull had strong, sharp, carnivorous 

 teeth, indicating 

 that the creature 

 was a fierce, pre- 

 daceous animal. 

 The use of the 

 crest on the back 

 is unknown, and 

 aside from its 

 presence the ani- 

 mal was very 

 primitive in 

 structure. Some 

 members of this 

 group (Varano- 



saurus, Fig. 467) were swift-running reptiles, living in the forests, 

 hiding under logs, and feeding on the numerous cockroaches and 

 other insects. 



A third group, although inconspicuous in the Permian, were of 

 great importance both because of their great development in the 



^V^ 



Fig. 466. — Dimetrodon, a spiny but primitive reptile from the 

 Permian of Texas. (Modified after Jaekel.) 



