l'.)l().J Characters of the Antcdral Crcodonts. 307 



iiivorous adaptation, {h) The pelvis always has a stout puboischiadic 

 symphysis. In Dromoryon however the pelvic outlet as figured by Wortman 

 (/. c, 1901, p. 425) is very small, but not as small as it is in Lipotyphlous 

 Insectivores. (r) The limbs are longer or at least not so much bent and 

 generally better fitted for cursorial habits; the feet are digitigrade rather 

 than plantigrade, {d) In the manus and pes of Creodonts the subequality 

 and symmetrical arrangement of digits II, III and IV, which is characteristic 

 of the Insectivora (p. 254), is less marked. In DromocAjon, as figured by 

 Wortman (Nov. 1901, p. 3S2 anil Dec. 1901, i)l. vii), digits III and IV of 

 both manus and })es are very distinctively paired and so also are digits II and 

 V. In Sinopa, as figured by Matthew, 1906, pp. 224, 228), this condition 

 is nuich less pronounced and some slight approach is made to the Insectivore 

 condition; the Insectivore resemblance is more marked in Patriofelis, as 

 figured by Osborn (1900, p. 269). In the Creodonta Inadaptiva the ungual 

 |)halanges are cleft, whereas in most Insectivora (except Talpidtie, Chrysoch- 

 loridjie) they are uncleft, as in the Creodonta Adaptiva (p. 308). 



Conclusions. All such differences however seem to be due to the diverg;- 

 ent habits of the Insectivora and Creodonta and to the necessity of com- 

 ])aring Eocene Creodonts with recent Insectivores, and do not in themselves 

 imply a very ancient separation between them. But in view of the presence 

 of fairly large Creodonts in the Basal Eocene it is probable that the separation 

 of the Creodonts and Insectivores must long antedate the beginning of the 

 Tertiary. 



In fine the Mesozoic ancestors of the Carnivora were probably small, 

 semiarboreal, insectivorous and partly carnivorous Placentals, with a dental 

 formula of f^xl!* ^ well developed milk dentition, small tri tubercular upper 

 molars, simple premolars, small simple canines, incisors of opposite sides 

 arranged in a convergent rather than transverse series. The muzzle was 

 broad and heavy, the skull constricted back of the orbits, the brain case very 

 small, probably surmounted by a long low sagittal crest, the zygomata not 

 large, the optic foramen independent, and an alisphenoid canal present. 

 The skeleton retained many primarily arboreal adaptations. These hypothe- 

 tical forms thus approached the ancestral Insectivores (p. 254) but very early 

 began to emphasize the flesh- eating, raptorial habits and structures, to in- 

 crease in size and to spend more time on the ground. As thus conceived 

 they would resemble the contemporaneous Polyprotodont Marsupials in 

 many characters but they may have been distinguished from them by the 

 following characters among others: 



(1) Entocarotid entering through foramen lacerum medium, an ali- 

 sphenoid canal, a distinct optic foramen. 



