.8,,,. STUDY OF MAMMALS DURING 1891. 107 



South American mammals, which may some day, when their true 

 affinities are known, afford important aid in constructing the table of 

 mammalian genealogy. 



That very similar structural peculiarities may arise separately 

 in different groups is indicated by Dr. W. B. Scott's investigation 

 into the phylogeny of the Camels and their allies; •♦ where it is shown 

 that the crescent-like (selenodont) grinding surfaces of the molar 

 teeth of these animals have almost certainly been developed quite 

 independently of those of the true Ruminants, which have a similar 

 general structure. Indeed, it appears that we must go back as far 

 as the small Eocene Ungulate known as Dichobunus (represented in 

 North America by the closely allied, if not identical, Homacodon) 

 before we reach what can be regarded as the common ancestral 

 type of both the Camels and the true Ruminants. 



That the evolution of the Camels took place in the New World 

 has, for some years, been regarded as a fairly well ascertained fact, 

 but it has been reserved for Dr. Scott to work out this phylogeny in 

 a thoroughly satisfactory manner. It would be out of place to detail 

 here the names of the various extinct genera connecting the modern 

 Camels and Llamas with their primitive ancestral types ; but we may 

 observe that, as we descend the geological scale, we gradually find a 

 less and less reduction in the number of the teeth below the normal type, 

 accompanied by a steadily decreasing bodily size, till, in the American 

 Miocene Pocbrothevium, we have an animal not much larger than a 

 fox, with the full mammalian complement of teeth, and the metapo- 

 dial bones of the feet not soldered together to form cannon-bones. 

 Although this animal had acquired selenodont teeth, yet it is but a 

 single step to a creature like Dichobunus, in which the molar teeth 

 still retained the primitive hillock-like (bunodont) cusps of those of 

 the pigs. Dr. Scott considers that towards the end of the Miocene 

 epoch the ancestors of the modern Camels and Llamas respectively 

 migrated to the Old World, and the southern half of the New ; the 

 earliest known Old World Camels being those of Northern India, 

 which retain certain signs of kinship with the Llamas, which are 

 lost in the living species. 



The above' appear to us to be some of the more striking results 

 of the year's work in mammalogy ; but there are, of course, many 

 other topics of nearly or quite equal interest, which we are debarred 

 from noticing by the necessary limits of our article. 



R. Lydekker. 



* On the Osteology of Po'ebrotherium : a contribution to the Phylogeny of the 

 Tylopoda. Jomn. MorphoL, vol. v., pp. 1-78, pis. i.-iii., 1891. 



