B 



MORRISON MAMMALS: MULTITUBERCULATA 7 



are, therefore, nearly or quite contemporaneous. The upper Cretaceous mammals come 

 from two or three distinct, successive horizons, but they constitute an essential faunal 

 unit not possible of division at present, and their treatment together is entirely justi- 

 fiable whether from a zoological or geological point of view. 



^. MAMMALS OF THE MORRISON 

 FORMATION, UPPER JURASSIC 



The mammalian fauna of the Morrison formation is at present by far the largest and 

 most important of the entire Mesozoic. Although it is exceeded in the completeness of 

 individual specimens by the South 

 African Stormberg and the Mongo- 

 lian Djadokhta, yet it leads almost 

 incomparably in the number and 

 variety of known forms and it is the 

 real basis of our present knowledge 

 of Jurassic mammals. As is brought 

 out more fully elsewhere, it is essen- 

 tially contemporaneous with the 

 rich Purbeckian mammalian fauna 

 of England. The families, the gen- 

 era, and, where necessary, the spe- 

 cies of the two faunas have been 

 very closely compared. 



Four orders here occur : Multi- 

 tuberculata, Triconodonta, Sym- 

 metrodonta, Pantotheria. In the 

 following revision seven families, 

 twenty-four genera, and forty spe- 

 cies are recognized. The number of 

 genera and species would be some- 

 what reduced by the discovery of 

 associated material, but the fauna 

 will remain comparable to many 

 Tertiary mammalian faunas in 

 variety. 



p'—vsacs 



Fig. 2. Diagrams to illustrate terms applied to molar cusps 

 and their abbreviations. A, Priacodon, lower molar. B, 

 Tinvdon, lower molar. C, Dryolestes, lower molar. D, 

 Lance didelphid, lower molar. E, Melanodon, upper mo- 

 lar. F, Gypsonictops, upper molar. 



a, b, c, the anterior, median, and posterior cusps, respec- 

 tively, of triconodonts or symmetrodonts. Am, amphicone, 

 or median external cusp of pantothere upper molars. End, 

 entoconid. Hid, hypoconulid. Hy, hypocone. Hyd, hypoco- 

 nid. Me, metacone. Med, metaconid. Ml, metaconule. Mts, 

 metastyle. Pa, paracone. Pad, paraconid. PI, paraconule. 

 Pr, protocone. Prd, protoconid. Ps, parastyle. Tad cusp, 

 talonid cusp of pantotheres. 



Order MULTITUBERCULATA Cope 



Definition. — Upper incisors primitively three, the first much reduced or lost, the 

 second enlarged. One enlarged lower incisor. No canines. Molars with five or more 

 cusps arranged in two parallel longitudinal rows in the lower jaw, in two or three 



