A NEW FOSSIL REPTILE FROM UTAH — GILMORE 113 



RELATIONSHIPS 



At the present time so little is known of the skeletal structure of 

 Plnacosuchus mantiensis that I have been unable to arrive at a 

 satisfactory conclusion as to its true ordinal affinities. Of the 14 

 reptilian orders recognized by Woodward r the specimen under dis- 

 cussion can be satisfactorily eliminated from 10. This leaves the 

 Squamata, Thecodontia, Crocodilia, and Dinosauria, and it is in 

 one of these orders that this specimen will eventually find a perma- 

 nent resting place. 



The presence of a thecodont dentition and the amphicoelous verte- 

 brae would appear to rule it out of the Squamata, for with the 

 exception of the Gekkota, which have amphicoelous vertebrae but 

 always combined with an acrodont dentition and absence of bony 

 scutes, all other lizards and all other members of the order have 

 procoelous vertebrae. 



That this specimen could be referred to the Dinosauria seems 

 highly improbable, for although the primary number of sacral verte- 

 brae in this order may have been two, no Upper Cretaceous dinosaur 

 is known having less than five, and several genera have many more 

 than that. This reason alone would appear sufficient to exclude 

 Plnacosuchus. 



The order Thecodontia is a generalized group from which it is 

 thought by some authorities that both the Crocodilia and the Dino- 

 sauria may have been derived, but the suborder Pseudosuchia con- 

 tains a considerable number of lizard-shaped land reptiles of small 

 size that have such a diversity of structure that their location here 

 must be regarded as provisional. As a repository for genera of 

 uncertain ordinal affinities the Pseudosuchia would seem to be the 

 logical reference of P'macomchus. The few structural features 

 known would not be in particular discord with such an assignment, 

 but the fact that all the referred genera are of Triassic age or older 

 leads one to doubt the advisability of such an assignment. 



Amphicoelian crocodilians are known to have persisted into the 

 Upper Cretaceous (Benton), and the present specimen presents a 

 few characteristics that suggest crocodilian relationships. Reference 

 is made to the thecodont dentition, sacrum of two vertebrae, presence 

 of bony skin scutes, close resemblance of incomplete coracoid to that 

 of the crocodile, and a sculpture of the maxillary surface closely 

 simulating that of many crocodilians. Meager and unsatisfactory 

 though the evidence may be, none of the more important characters 



1 Woodward, A. Smith. Zittel's "Textbook of Paleontology," vol. 2, pp. 233-427, 1932. 



