408 NOTES ON THE CANID^E OF THE WHITE RIVER OLIGOCENE. 



eral of which, like the shape of the radius, recur in CynocUctls. Tending to the same 

 conclusion is the fact that what little is known of the structure of the creodont 3Iiacis 

 is of similar composite canine-feline character and it is to that creodont family to which 

 most of the lines of fissipede Carnivora appear to lead back. It may be hoped that the 

 problem will receive its definite solution when we shall have recovered the as yet miss- 

 ing or very imperfectly known dogs from the Uinta, uppermost AVhite River and lowest 

 John Day formations, and are thus enabled to trace the successive changes step by step. 



Assuming, then, as probable that Daphcenus should have a place in the direct canine 

 phylum, the larger question at once arises: What was the relation between the early 

 members of the Canidce and Felidce, and of both of these groups to the other fissipede 

 families ? It seems to be a comparatively rare phenomenon among the mammals that 

 parallelism or convergence of development should be manifested in all parts of the struc- 

 ture of two independent lines, though that this may "happen is shown by the case of the 

 Machairodonts and felines, to which reference has already been made. Usually, however, 

 parallelism is displayed in a few structures only, such as the dentition, or the feet, or the 

 vertebrae, and the more widely separated any two phyla are at their point of origin, the 

 less likely are they to develop along similar lines. It will be sufficiently clear from the 

 foregoing descriptions that the resemblances between Daphcenus and the more primitive 

 Machairodonts, such as Dinictis, are not only exceedingly close, but that they recur in 

 all parts of the skeleton. The skull, the vertebral column, the limbs and the feet are 

 all so much alike in the two series that, in the absence of teeth, it is often very difficult 

 to decide to which of the two a given specimen should he referred. Such close and gen- 

 eral resemblance is prima facie evidence of relationship, even though it should have been 

 independently acquired, because parallelism is much more frequent between nearly allied 

 than between distantly related groups. In the preseni instance, however, there is no rea- 

 son to infer that the resemblances were separately attained ; on the contrary, the evidence 

 now available seems to favor the conclusion that the dogs and cats are derivatives of the 

 same Eocene stock. It cannot be pretended that this conclusion is, as yet, a well-estab- 

 lished one, inn- can it be so established until we recover the missing links of the canine 

 and feline genealogies. Daphamus may eventually prove to be merely an abortive side- 

 branch without phylogenetic significance, though this seems unlikely in view of its rela- 

 tionship to the John Day dogs. < >n the other hand, when we have learned more of the 

 Uinta dogs, it may appear that all the many resemblances of Daphcenus to the Machai- 

 rodonts have been separately attained : but existing evidence does not favor this sug- 

 gestion either. It seems exceedingly likely that the dogs and cats are more closely 

 related than has hitherto been believed and that they were derived from a common mid- 

 dle or late Eocene progenitor. 



