MORRISON MAMMALS: PANTOTHERIA 



49 



cheek tooth number, with retention or slight exaggeration of the elongate molars, and 

 the dryolestids largely by anteroposterior compression of the molars with retention or 

 slight exaggeration of the high cheek tooth number. A rather imperfect analogy is 

 seen in the splitting of the Insectivora into the dilambdodont and zalambdodont 

 groups. According to this view Amph'ttherium nearly represents the primitive condi- 

 tions among Pantotheria. It is the earliest pantothere known and, as has been empha- 

 sized in the author's treatment of it (1928B), its characters are such that any other 

 pantothere could be derived from it by changes which are of quite the same sort as have 

 been demonstrated beyond doubt in other lines of mammals. In its high cheek tooth 

 number it resembles the dryolestids, and in its relatively elongate molars it resembles 

 the paurodontids, although without various minor specializations seen among the 

 latter. 



Paurodon Marsh 1887 

 1887. Paurodon, Marsh, Amer. Jour. Sci. (3) XXXIII, 342. 



Definition. — Dental formula I? Ci /'' ^ 



P2 Mi. Pa'' and talonid shelf-like, not form- 

 ing true cusps, me'' very low. Talonid semi- 

 circular in plan. With postcanine diastema, 

 molars spaced. Horizontal ramus stout. 

 Symphysis short. Coronoid arising some 

 distance posterior to last molar. 



Type. — P. valens Marsh. 



Distribution. — Morrison formation, 

 Wyoming. 





/■ 



—-../ 





PAURODON 



Fin. 23. Paurodon. Diagrammatic internal 

 view of right lower jaw. Three times natural 

 size. 



Paurodon valens Marsh 1887 

 1887. P. valens, Marsh, Amer. Jour. Sci. (3) XXXIII, 342. 



Type. — U.S.N.M. No. 2143. Left lower jaw with C, P1-2 and M1-4. 

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

 Diagnosis. — Sole species of the genus. First three molars each 1.2 mm. in length, 

 M4 i.o mm. in length. 



Dentition 



The first tooth preserved is certainly a canine and not a premolar as suggested by 

 Gregory (1922, p. 50). It is high, oval in section, with the tip excavated internally, 

 and stands nearly erect, pointing but little forward. The root is also oval in section and 

 is undivided. The longer axis of the section of the root is inclined outward anteriorly 

 at about 30° to the long axis of the jaw. 



Posterior to the canine is a diastema of about the same length, and then follow the 

 six evenly spaced cheek teeth. The first of these has two roots, is laterally compressed, 

 and has a posterior heel from which an internal cingulum runs forward and upward. 



