CREODONTA 



609 



blade having a large inner cusp. The upper teeth closely resemble 

 the molars of Dasyurus, while the lower molars are like the lower 

 carnassial of Cynodidis and Viverm; and thus indicate how the 

 Creodonts may have passed into the true Carnivores through the 

 extinct Miacidce. 



Ardocyonidce and Mesonychidce, The first of these families is 

 represented by Ardocyon primcevus, one of the oldest known Tertiary 

 mammals, from the lowest Eocene beds of La Fere, department of 

 Aisne, France, and also by other species from corresponding beds 

 at Eheims. The dental formula is i f , c ^, p g^ m f . The upper 

 molars (Fig. 279) are tritubercular, with an incipient postero- 

 internal column (hypocone) ; 

 the lower are quadrituber- 

 cular ; and the premolars 

 simple. The typical species 

 was of large size, but the 

 two of which the teeth are 

 figured were considerably Flo 279 ._ The three rig ht upper molars of Arcto- 



Smaller. In the American cyan dueli (a), and the second of A.gen-aisifb); from 



Mesonm the dental formula the Lowest Eocene of Rheiins - **> P rotocone ; P*. 



y . . , paracone ; me, metacone ; hy, hypocone ; ml, meta- 



WaS the typical One, the jaWS conule ; j>Z, paraconule. (From Osborn.) 



were comparatively short, the 



mandibular symphysis was elongated, the cheek-teeth were of 

 simple structure, and resembled the premolars of many of the true 

 Carnivora, and the astragalus had a grooved tibial surface and 

 distinct distal facets for the cuboid and navicular, resembling in the 

 latter respect the corresponding bone of a Perissodactyle Ungulate. 

 The terminal phalanges had deeply fissured extremities, and are said 

 to be more like those of Rodents than true Carnivores. Mesonyx 

 ossifragus was larger than a Grizzly Bear. Amblydonus, of the same 

 deposits, differs by the smooth tibial face of the astragalus and the 

 development of an anterior cusp to the lower molars. 



39 



