64 AMERICAN PERMIAN VERTEBRATES 



so closely the temporal structure of the real amphibians, while, 

 on the other hand, real temnospondyls should mimic equally 

 curiously the temporal condition of the higher reptiles. 



Of the skeleton back of the skull the structure is largely primi- 

 tive both in the pectoral girdles and limbs and the vertebrae, which 

 approach those of the temnospondyls more closely than do those of 

 any other known reptile. The absence of the cleithrum differ- 

 entiates the form, though not widely, from Diadectes, Limnoscelis, 

 and Pareiasaurus. The pectoral girdle offers nothing distinctive. 

 The presacral vertebrae differ widely from those of Limnoscelis, 

 Diadectes, and Pareiasaurus in the almost entire absence of dorsal 

 spines, and the great lateral expansion of the arches, agreeing 

 much better with those of Labidosaurus. Indeed, the vertebrae 

 of this last genus are, in their general characters, so similar that 

 they have been confused. Nor is there anything distinctive in 

 the pelvis; it, too, is of the " old-fashioned " type. In the limbs, 

 however, we get certain apparent resemblances that would seem 

 to ally the genus with Diadectes and Limnoscelis, but, as I have 

 stated elsewhere, I have little faith in the genetic value of these 

 characters. I believe they are more of an adaptive nature. Not 

 only do the limbs resemble those of Diadectes and Limnoscelis more 

 than those of Labidosaurus, but this resemblance extends to the 

 temnospondylous amphibians as well, especially Eryops, in the 

 short legs, short, thickset mesopodials, broad feet, enormous 

 humeral entocondyle, the presence of an ectepicondylar process, 

 very large adductor crest, and enormous digital fossa of the femora, 

 etc., as well as the general absence of condylar ossifications for 

 in all these forms the joints were formed largely by cartilage 

 which never ossified and the sutures remained separated longer 

 and more completely than in the Pariotichidae. 



However, it is very much of a question whether these 

 resemblances are so much the result of heredity and relationships 

 as of adaptive, parallel, or convergent evolution. We have been 

 speculating on the presumption that the known temnospondylous 

 amphibians like Cacops, Eryops, Euchirosaurus, are, if not the 

 actual ancestors of the reptiles, their first or second cousins. But 

 this presumption is, in my opinion, quite unjustified. Moodie 



