54Q ORIGIN OF MAMMALS xix. 4- 



condition, in that the bones were moderately elongated and slender 

 and the limbs perhaps tended to be held vertically under the body. 

 However, there was no great development of a backwardly directed 

 elbow and forward knee. The teeth were considerably specialized, 

 possibly for eating molluscs, and there were several rows of crushing 

 teeth on the edge of the jaw, and long overhanging ones in the 

 premaxillae. 



5. Order *Pelycosauria (= Theromorpha) 



The synapsid line began when an early offshoot from some such 

 anapsid as *Captorhinus developed a temporal fossa. This must have 



Dimebrodon Varanosaurus 



Fig. 317. Skulls of two early synapsids. (After Romer, Vertebrate Paleontology, 

 University of Chicago Press, and Abel.) 



occurred in the middle of the Carboniferous, nearly 300 million years 

 ago, producing in the later part of that period, and in various Pennsyl- 

 vanian and Lower Permian strata, especially in North America, these 

 earliest synapsid populations, classified together as pelycosaurs or 

 Theromorpha. *Varanosaurus (Fig. 317), from the Texas Red Beds, 

 is a typical example, a carnivore, about 3 ft long, showing a lizard-like 

 appearance little different from that of anapsids or primitive diapsids. 

 Intercentra were found all along the vertebral column, as in anapsids, 

 and there were abdominal ribs. The teeth showed the beginnings 

 of the mammalian differentiation in that one or more near the front 

 of the series were elongated as 'canines'. The skull of pelycosaurs also 

 showed tendencies in the mammalian direction in having a long 

 anterior region and a relatively high posterior part, giving a large 

 brain-case and deep jaw. 



Other pelycosaurs developed long neural spines, in more than one 

 line, *Edaphosaurus and its allies being herbivores, some of them as 

 much as 12 ft long, whereas *Dimetrodon (Fig. 317) was a carnivore. 

 The spines presumably supported a web, perhaps used in temperature 

 regulation. These animals were important in the late Carboniferous 

 and early Permian fauna, preying on the other early reptiles and on 



