42 



AMERICAN MESOZOIC MAMMALIA 



out doubt a spalacotheriid and probably the upper dentition of S-palacotherium itself. 

 This makes it possible or even probable that the present upper jaw also belongs to the 

 Spalacotheriidae rather than to the Amphidontidae. Reference to Tiiwdon would be 

 possible, but in view of the very doubtful character of the evidence and of the lack of 

 association it seems less misleading to give a new generic name, Eurylambda, to 

 " Amfhidon" aequicrurius. 



Eurylambda aequicrurius (Simpson 1925) 

 1925. Amfhidon aequicrurius, Simpson, Amer. Jour. Set. (5) X, 463. 



Type. — Y.P.M. No. 13639. Part of right maxilla with one molar. 



Horizon and Locality. — Morrison formation. Quarry 9, Como Bluff, Wyoming. 



Diagnosis. — Sole species of the genus. Length of known molar 2.0 mm. 



Order PANTOTHERIA Marsh 



Definition. — Incisors not specialized. Canines present, often bifanged. Premo- 

 lars generally piercing and trenchant, never fully molariform and usually quite unlike 

 the molars. Molars primitively trigonal, interlocking, and always to some extent over- 

 lapping in occlusion. The upper molars with 

 one main inner cusp and one main outer cusp 

 (which may be much reduced) and always two 

 or more other cusps variously developed. The 

 lower molars with an asjonmetrical trigonid of 

 three cusps (or rarely more) and a talonid 

 which is primitively unbasined and with a sin- 

 gle cusp but in the most specialized family 

 (Docodontidae) is basined and with more than 

 one cusp. Lower molars sometimes with an 

 outer, but never with an inner, cingulum. Primi- 

 tive cheek tooth formula apparently P4 M^, but 

 may be considerably reduced. Mandible not 

 ankylosed at symphysis, with distinct coronoid, 

 condylar, and angular processes. Angle not in- 

 flected. 



Distribution. — Middle Jurassic, Eng- 

 land. Upper Jurassic, England, United States, 

 East Africa. 



Fig. 19. Morrison mammals. External, 

 crown, and anterior views of typical 

 right upper molars. A, Priacodon. B, 

 Eurylambda. C, Melanodon. D, Doco- 

 don. Not to scale. 



This is the most abundant, most varied, and, from a phylogenetic point of view, 

 most important of the Jurassic orders of mammals. In view of the extent to which the 

 other Jurassic mammals, although very unlike any of the Tertiary or recent orders, 

 have been subordinated to the latter in the usual classifications, it is not surprising to 



