84 AMERICAN MESOZOIC MAMMALIA 



The last molar is about as broad as the preceding one and is much shorter. As 

 usual for last molars, its obliquity is in the opposite direction from that of the preced- 

 ing tooth. The raised edges of the basin do not bear any distinct cusps and there is a 

 distinct but low and rounded ridge running down the otherwise concave external face 

 of the internal cusp, but this ridge does not cross the basin. The anteroexternal heel is 

 very distinctive, accentuating the hook-like apex and smooth, hemispherical external 

 surface seen on the preceding molar. 



Measurements 



Length Width 



Antepenultimate M 1.3 i.i 



Penultimate M 1.3 1.4 



Last M 0.8 1.3 



Docodontidae^ new name 



1887. Diflocynodontidae, Marsh, Amer. Jour. Set. (3) XXXIH, 338. 



1888. Dicrocynodontidae, Osborn, Am. Nat., XXH, 1078. 



Definition. — Upper and lower molars subquadrate, complicated by the presence 

 of cusps not seen in other known pantotheres. Lower molars supported by two subequal 

 roots and with relatively large basined heels with two talonid cusps. Nine (?) to 

 twelve cheek teeth. 



Type. — Docodon Marsh. 



Distribution. — Upper Jurassic, England and North America. 



This family includes the most peculiar and highly modified of the pantotheres. 

 Their molars are much the most complicated dental structures known from the Juras- 

 sic or, indeed, with the possible exception of some of the Cretaceous multituberculates, 

 from the entire Mesozoic. This peculiarity was recognized by Marsh who in 1887 

 created for them the distinct family "Diplocynodontidae." Osborn at first (iSSSa) 

 referred Marsh's genera to the Amphitheriidae, but this was based on erroneous con- 

 ceptions both of Amfhitherium and of the docodontids and was soon corrected by 

 Osborn himself. No subsequent doubt has been cast upon the unity of the group and its 

 right to separation from all other pantotheres. 



Some doubts have, indeed, been cast on the right of the Docodontidae to inclusion 

 in the Pantotheria, although such a position is usually accepted. Gidley (1906, p. 

 105), in accordance with his known extreme polyphyletic conception of mammalian 

 evolution, stated that the molars of "Dicrocynodon" were apparently derived from the 

 simple reptilian cone independently of the molars of Dryolestes, — a view which would 

 logically lead to placing this genus in an order, subclass, or even class distinct from 

 that to which the other pantotheres are referred. As this was based on the most exact 

 knowledge of docodontid molar structure hitherto attained, it is worthy of considera- 

 tion, although further analysis seems to disprove it beyond any question. Gregory 

 (1922, p. 59-60) stated that he had failed to find a solution of the problem of occlusion 



