48 AMERICAN MESOZOIC MAMMALIA 



Family Docodontidae, new name. 

 *Docodon Marsh 1881 

 Peraiocynodon Simpson 1928 



The genera marked * occur in America, the others only in England, except Bran- 

 catherulum, which is from East Africa. 



PAURODONTIDAE Marsh 1887 



Definition. — Cheek teeth P4 M4 or less. Trigonid elongate, not compressed 

 anteroposteriorly, me'' markedly lower than pr**. Talonid not reduced, semicircular or 

 triangular in plan, with one cusp, posterior or posterointernal in position. Lower 

 molars supported by two large subequal roots. Lower jaw usually short and stout. 



Type. — Paurodon Marsh. 



Distribution. — Purbeck beds, England. Morrison formation, Wyoming. 



Founded for the single genus Paurodon, the validity of this family has been 

 rather generally recognized. Gregory (1922), however, has provisionally united it 

 with the Amphitheriidae, stating that its maintenance as distinct would depend on 

 confirmation of Marsh's description of Paurodon. The present research has shown that 

 Marsh was correct in all essentials and the family is therefore reinstated. The five 

 genera placed here constitute a rather heterogeneous assemblage. Archaeotrigon is 

 surely related to Paurodon. Tathiodon approaches the dryolestids in some respects, 

 although the characteristic anteroposterior compression of the molars in the latter 

 group is absent and the number of cheek teeth is markedly less. Peramus is widely 

 distinct from the dryolestids, but is in many respects intermediate between the typical 

 paurodontids and Amfkitherium, so that its reference to the Amphitheriidae, where it 

 has usually been placed hitherto, would be possible. Brancatherulum is very poorly 

 known, being based on a broken jaw without teeth, but it is probably closely allied to 

 Peramus. 



Aside from the aberrant Docodontidae, there are two families of pantotheres in 

 the upper Jurassic: one, the Paurodontidae, with few molars, not compressed longi- 

 tudinally, the other, the Dryolestidae, with many molars, compressed longitudinally. 

 It might be supposed either that the dryolestid condition was primitive and the pauro- 

 dontids have the molars secondarily elongated consonant with their reduction in num- 

 bers, or that the reverse is true, that the paurodontids are primitive and the dryolestids 

 have the molars secondarily shortened consonant with their increase in numbers. The 

 question is a theoretical one, not now possible of definitive solution, and somewhat out- 

 side the plan of the present memoir which is chiefly devoted to an exposition of what is 

 positively known, but a few brief remarks on the subject are necessary, if only as a 

 caution against unwarranted speculation. The probabilities at present seem strongly to 

 favor the view that neither of these suppositions is true. It seems probable that the 

 ancestral condition was one with many molars, not compressed longitudinally. From 

 this type the paurodontids would seem to have been derived largely by reduction in 



