8o 



PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 



flexed, with the articular surfaces of the centra in contact or parallel, the head 

 would be folded under the breast, the pointed cervical spines projecting directly 

 forward. That such a posture was possible seems certain ; that it was an habitual 

 posture of the animal in life, either of offense or defense, it would be hazardous to 

 say; and yet one can not resist the belief that it was. 



The function of the greatly elongated spines in both this genus and Dimetrodon 

 has been the subject of no little speculation and some very fanciful theories. There 

 is little evidence that the spines were covered in life by a horny epidermis. They 

 of course could not have projected freely without a nutrient covering of some kind. 

 If, on the other hand, they were enveloped in a continuous covering, there could 

 have been little or no motion of the vertebral column in a vertical plane, since even 

 the slightest angle of divergence of the centra would have increased the distance 

 between the spines enormously at the periphery. The looseness of the cervical 

 vertebree is almost certain evidence of the possibility of considerable flexion and 

 that the spines throughout most of their extent could not have been connected 



Fig. 51. Edaphosaurus sp., X K. No. 3333, University of Michigan. A, frontal; 

 B, basioccipital, upper surface; C, basioccipital, lower surface. 



by ligaments, even elastic ligaments. They must have been freely movable in the 

 cervical region at least, probably invested by a firm skin.* 



It is a curious fact that no genus of vertebrates is more commonly met with in 

 the Texas Permian deposits than Edaphosaurus; isolated and fragmentary bones are 

 found everywhere ; a day seldom passes that the collector does not see one or more 

 Edaphosaurus vertebrae. It is also very rarely that he finds two or more verte- 

 brae in anatomical relationship, and hitherto there has been no record of the posi- 

 tive association of any other parts of the skeleton, except the pelvis. A legitimate 

 conclusion from these facts would seem to be that Edaphosaurus was an inhabitant 

 of the river plains and not of the more quiet bays and mud flats. The skeletons 

 were broken up and brought down to the lower lands by streams and freshets. 

 WilUston has figured and described f a leg of a reptile that he suspected belongs 

 with Edaphosaurus. It is peculiar in having a relatively long and slender femur and 

 short tibia and fibula, characters invariably associated with aquatic habits in 

 extinct reptiles. If this leg really belongs with Edaphosaurus, and there seems to 

 be a similar relation between the humerus and radius, it would add to the prob- 

 ability that the species of Edaphosaurus were more or less swimming, fluviatile 

 animals, living along the river plains and subsisting upon fresh-water mollusks and 



* Case has shown that in Chameho cristalus the elongated spines of the dorsal region are united by a 

 flexible skin, with a strong thread of connective tissue running along the apices of the spines. A few scat- 

 tered fibers of muscular tissue were found between the spines. This suggests the condition that existed in 

 the long-spined pelycosaurs. (Case, Science, xxi.x, p. 979.) 



t American Permian Vertebrates, p. 75. 



