MATTHEW, CLIMATE AND EVOLUTION 313 



result of post-Pliocene immigration and differentiation. Most of the 

 creodonts, he informs us, "died out with the Eocene or rather they were 

 modernized into the typical Carnivora in various parts of the world. 

 Some, however, kept on to almost recent times as highly specialized 

 creodonts, e. g. the sabre-toothed tigers : Nimravus in North American 

 Oligocene; Machcerodus from Miocene to Pleistocene in Europe and 

 Asia, whence in the Pleistocene it appeared as Smilodon in America. 

 . . ."^-^ It is perhaps unnecessary to point out that the machasrodonts 

 were not creodonts but typical Carnivora of the family Felidte, and that 

 their evolutionary series is fully as complete and progressive in the 

 Nearctic as in the Palasarctic record. I may also note that "small swine" 

 (meaning I suppose the primitive bunodont artiodactyles from which 

 both pigs and peccaries are derived) appeared in North America quite 

 as early as in Europe; that the genera Procamelus and Plmuchenia do 

 not mark the splitting of the Camelidae into camels proper and llamas; 

 that Dorcather-iuni is not identical with "Hyomoschus" {Hycemoschus) 

 and is an older name ; that Arsinoitherium is not a pair-horned dicera- 

 there but is a representative of a distinct order of mammals; that the 

 precise relations of the American Eocene tapirs have yet to be deter- 

 mined ; that Protapirus does not first appear in the Lower Oligocene of 

 Europe but in the Mid-Oligocene of Europe and North America ; that 

 there is no reason to believe that the European Paratapirus is more di- 

 rectly in line of descent of the later tapirs than is the so-called Tapiravus 

 of the American Miocene, and that the very fragmentary and inadequately 

 studied record of the evolution of the Tapiridas is quite inadequate for 

 the positive and exact statements which Gadow makes as to their "wan- 

 derings." 



The statements as to the evolution of the horse show a surprising 

 amount of inaccuracy, considering that this is so widely known a story. 

 Apparently, it is in part the result of an attempt to criticize and modify 

 the conclusions of American writers on the basis of a hasty survey of 

 the incomplete materials available in European museums. The Eocene 

 ancestors are disregarded, because they "are still so very generalized that 

 they lead to horses, rhinos and tapirs as well as to other distinct groups." 

 AVhile this is not far from the fact as regards the Lower Eocene Eohippus, 

 it certainly is not ti-ue of Orohippus and Epihippus of the Middle and 

 Upper Eocene. The relations of Miohippus to Mesoliippns are hardly 

 to be dismissed with a "perhaps." Desinatippus is not an ancestor of 

 Parahippus but is identical ; Hi/pohipjnis is not intermediate between 

 Para- and Merychippus but is an aberrant type descended from Miohippus 



1-8 Ol). (it. 



