MORRISON MAMMALS: PANTOTHERIA 



71 



B 



Herpefairus Simpson 1927 

 1927. Herpetairus, Simpson, Anier. Jour. Sci. (5) XIII, 413. 



Definition. — Dryolestid upper jaws with seven molars, each markedly shorter 

 than broad. Three external marginal cusps on upper molars, the central one largest. 

 Distinct posterior intermediate cuspule, but no other anterior or posterior marginal 

 cusps. Median transverse crest absent or (in a species doubtfully referred) faint. Last 

 premolar with both external and internal cingula, with a single small posteroexternal 

 cingulum cusp. 



TvPE. — Herpetairus arcuatus (Marsh). 



Distribution. — Morrison formation, Wyoming. 



With this genus begins the description 

 of the Morrison pantothere upper jaws. The 

 t)'pe species was referred to Dryolestes by 

 Marsh. It probably belongs either to this 

 genus or to Laolestes, but it is quite impos- 

 sible at present to correlate it definitely and 

 therefore, as already explained, a new ge- 

 neric name is provisionally applied to it. 



These upper molars are surprisingly 

 different from anything known from later 

 deposits. Each is quite sui generis. The cor- 

 relation of the various cusps with those 

 found in the primitive upper molars of the 

 Cretaceous and Paleocene is an exercise 

 rather in philosophical odontology than in 

 morphology. This is an important task to 

 which the writer hopes to return elsewhere 

 in adequate detail, but as regards probabil- 

 ity and permanent value it is of a wholly 

 different order of magnitude from the more 

 sober and fundamental problems set for the 

 present revision. One fact, however, must 

 be insisted upon : these upper teeth are tri- 

 angular in outline but they are not tritu- 

 bercular either literally or functionally. 



The first tri tubercular upper molars known are from the upper Cretaceous. If related 

 at all to the tritubercular type (and the writer believes that they are) these pantothe- 

 rian upper molars must be adjudged pretritnbercular. For this reason, and to avoid a 

 premature commitment to theoretical views which might detract from the morphologi- 

 cal value of the following descriptions, the terminology of trituberculy is not here 

 used. The cusps are designated chiefly by descriptive phrases — a somewhat clumsy 

 device but apparently the best procedure at present. 



Fig. 27. Diagrams of occlusal relationships in tri- 

 conodonts and pantotheres. A, Priacodon. B, Lao- 

 lestes lower molars and Herpetairus upper mo- 

 lars. C, Docodon. Lower molars in heavier lines. 



Not to scale. 



