158 



REVISION OF THE PELYCOSAURIA. 



stem, wWcli persisted into the Triassic of Europe wlien they died out at the 

 end of the Permian in North America. Moreover it must be remembered 

 that the Triassic of North America is yet far from completely explored and 

 specimens similar to those of the Muschelkalk may j^et turn up on this 

 continent. 



The ideas expressed as to the relationship of the Pelycosauria may be 

 pictured by the following diagram : 



PEBMO-CARBONIFEROUS; 

 LINE UNCERTAIN 



BHYfJC HOC sew ALIA 



PROGANOSAUHIA 



PROTEROSAUfllA 



4NOMOSAURU3(7) 



OIMETROOON 



CTENOSAURUS 



NAOSAURUS 



fPOLIOSAURUS 



PRIMITIVE RHYNCHOCEPHALIA 



The sudden change in the direction of the line beyond Clepsydrops 

 indicates the beginning of the extreme specialization. 



With the fuller knowledge of the anatomy of the Pelycosauria it seems 

 hardly necessary to mention the unfortunate generalization of Cope in which 

 he placed the Pelycosauria in an ancestral relationship to the mammals. 

 This idea gained little credence, but the name Theromora, suggested by it, 

 has had an unfortunate and confusing effect upon the systems of classification. 



Jaekel has recently (136) made the suggestion that the spines on the 

 back of the Clepsydropidcc were free from the skin, and that when the animal 

 detected danger it threw the body into curves, causing the spines to stand out 

 in different directions and present a spiny front to all comers. This seems 

 but one more fanciful suggestion for the use of the spines. There is no 

 necessity for the assumption that the spines were free from the body, and, 

 as shown in the text above, p. 147, they were in all probability covered by a 

 thin but tough layer of skin. The ligament that bound the spines together 

 would be elastic and would not interfere with the bending of the body in a 

 vertical plane ; the vertebrae do not have zygosphene and zygantrum as 

 stated by Jaekel, and there was very little possibility of lateral movement, 

 certainly none of a partial rotation of the vertebrae on the notochordal axis, 

 as would be necessary if the spines were to point outward as indicated in 

 Jaekel's sketch. Moreover, the spinal column of the animal was short and 

 it could not be thrown into sinuous curves as supposed by Jaekel. 



