TRIMERORHACHIS, A PERMIAN TEMNOSPONDYL 

 AMPHIBIAN 



S. W. WILLISTON 

 University of Chicago 



No genus of vertebrates occurs so abundantly in the Permian 

 deposits of Texas and Oklahoma — it is unknown elsewhere — as 

 Trimerorhachis Cope. Almost always the remains are found in 

 bone-beds as masses, more or less cemented together, of isolated 

 and disturbed bones, often broken, sometimes waterworn, never 

 in anatomical relation. Isolated specimens are not often found, 

 and in such cases where parts of a single skeleton are associated 

 they are more or less jumbled together. The clavicular girdle only 

 is sometimes found closely associated with the skull, filling out 

 more or less the interval between the mandibles posteriorly. In 

 the Chicago collections there are probably parts of at least five 

 hundred individuals. I have counted seventy-five isolated occi- 

 pital condyles, nearly as many articular ends of the mandible, 

 and scores each of humeri, femora, ilia, scapulae, clavicles, and 

 epipodials, for the larger part fragmentary. Very often the bones 

 are associated with disconnected bones of Diplocaulus; not rarely 

 with teeth of Diplodus and dipnoans; and sometimes with the 

 smaller disconnected bones of land reptiles. All of which go to 

 prove that the various species of Trimerorhachis were purely 

 aquatic animals, living probably in shallow waters near the shores. 



Different writers have expressed the opinion, and I have shared 

 it, that Trimerorhachis is the most generalized of our American 

 temnospondyl amphibians. I am now about convinced that it 

 is the most specialized, for the following reasons : 



We have very good reason to believe that this and other 

 groups of stegocephs were, by the beginning of Permian times, 

 already very old. The origin of terrestrial amphibians surely dates 

 from at least as early as late Devonian times and of land reptiles 

 from early Pennsylvanian if not Mississippian times. There can 



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