CONTRASTED 

 FIELDS 



VERTEBRAL 

 STRUCTURE 



VERTEBRAE 

 NAMED 



While paleontologic knowledge is full and growing 

 for some groups, it is lean and almost dormant in other 

 branches. More investigation has been made in and more 

 papers have been written on the mammals than on all the 

 other classes of extinct vertebrates. Much has been written 

 on the reptiles, and this is a growing field, but the mammals 

 have the lead in present investigation and will probably 

 continue to hold it. On the other hand little has been 

 written on the lower vertebrates, with the exception of the 

 fishes, and probably little will be done for it is not a field 

 that will allow of much expansion because of the lack of 

 material. All that workers in vertebrate paleontology have 

 to use are the bones or hard parts of the extinct animal. 

 In a few and very rare instances the skin and the hair may 

 leave its impression. Fossil flesh has never been found 

 except in the case of a very few late Pleistocene or Sub- 

 Recent Mammoths. 



The structure of the vertebra, irrespective of size, 

 gives the key to the probable classification of an animal- 

 skeleton, e. g. 



Vertebra with the concavity in front are PROCOELUS. 

 Vertebra with the concavity in rear are AMPHOCOELUS. 

 Vertebra with no concavity, but flat, are PLATYCOELUS. 

 Vertebra with double concavity are OPISTHOCOELUS. 



All erect walking mammals are Platycoelus. All 

 snakes develop the additional articulating vertebral denti- 

 tion called "the zygosphene." Pterodactyls were the first 

 Procoelus animals. Crocodiles and lizards were the first 

 Amphocoelis animals, and did not become Procoelus until 

 the Cretaecous. Only land animals become Procoelus. The 

 Mososaurs are Procoelus but are a reverting-to-water type. 

 Dinosaurs are Opistocoelis, and like snakes the Cotylosaurus 

 and a few other amphibious Stegocephalians have the extra 

 articulating dentition of the zygosphenal type on the ver- 

 trebra. 



The kinds of vertebra by name are: Cervical, Dor- 

 sal, Lombar, Sacral, and Caudal. The Sacral vertabra are 

 from two to three in number and bear ribs for the support 

 of the pelvis. They are usually heavier than the others 

 for this reason. No living animal except crocodiles have 

 ribs on the atlas. "Seymouria" has but one sacral vertebra 



