MAMMALIAN DAWN. 8 1 



division of the Ungulates is of interest in being the most 

 numerous of the larger mammals now living, including all 

 the Ruminants and the pigs and hippopotami. This division 

 was well represented during the Tertiary, the earliest forms 

 apparently being the ancestors of the pigs, to which the hip- 

 popotami constitute a side group. The characteristic feature 

 met with in these primitive forms is the elevation of the 

 enamel of the crowns of the molar teeth to form tubercles, 

 while iu the Ruminants these elevations are flattened and 

 take the form of crescents. These, with correlated features, 

 furnish us two divisions of the Artiodactyla, the Tuberculate 

 Toothed (Bunodonta), and the Crescentic Toothed (Selen- 

 odonta), the former including the pigs and hippopotami, of 

 omnivorous habit, non-ruminating, and having a simple 

 stomach ; the latter the very large group of Ruminants which 

 are herbivorous, and have the complex stomach. There were 

 no Ruminants iu the Eocene, and throughout all of the Ter- 

 tiary bunodont dentition was common in the Artiodactyla. 

 But at the present time, after setting aside what has become 

 the very subordinate group containing the pigs and hippo- 

 potami, all the remaining pair-hoofed mammals belong with 

 the ruminating Selenodonts. 



Unique in several respects among existing Ruminants is 

 the family Camclidce, containing the camels and llamas, 

 which, in view of their cushion-like feet, have been placed by 

 zoologists in a distinct group — the Tylopoda. In addition 

 to this peculiarity the upper incisors have not entireh' disap- 

 peared as in other ruminating animals, and the skull does not 

 bear horns. The occurrence of llamas and camels in two 

 such widely separated regions of the earth as South America 

 and Asia remained unexplained until the distinct recognition 

 of the ancestors of this family in North America in an area 

 ranging from the Upper Eocene to the Upper Miocene. It 

 would appear from these discoveries that the family was 

 evolved during this time from primitive Artiodactyls, and 

 that by the Pliocene the fully differentiated camel had reached 



