THE UNGULATA, OR HOOFED ANIMALS. 135 



The palaeontologist, therefore, meets with Odd- 

 hoofed animals (Perissodactyla) as early as in the 

 Lower Eocene strata, and distinct from the Pair- 

 hoofed animals (Artiodactyla). He can, in both 

 groups, follow a few lines up to the present, and 

 can thus construct the pedigrees of the existing 

 families, at all events in very probable outlines. 

 In addition to the above-mentioned general form of 

 specialisation which received its fullest expression 

 in the ruminants and horses we have a very 

 marked change as regards the predominance and 

 the variations of the group in the New Tertiary as 

 compared with the Post Tertiary periods. The 

 tapir-shaped and pig-shaped Thick-skinned animals, 

 which at one time swarmed among the moist 

 forests and marshy banks, decrease in number, 

 while deer, antelopes, and oxen become more and 

 more the inhabitants of the newer formations 

 of forest lands and of the grassy plains or at 

 least the drier steppe-lands which became possible 

 with the greater consistency of the newer con- 

 tinents. Deer, antelopes, and oxen have, since the 

 Pliocene up to the Present, steadily and very 

 strikingly increased in number of species, whereas 

 the Odd-hoofed animals have as steadily decreased. 

 As late as 1869 Rutirneyer in special reference 



