MI LIFE OF TERTIARY PERIOD 227 



of this group are found in deposits of Middle Tertiary age 

 all over the northern hemisphere. They have two, three, 

 or four separate toes, and teeth much like those of swine. 



Another family, the Anoplotheridse, contains a variety of 

 animals which seem to be ancestral forms of the ruminants. 

 The genus Anoplotherium (Fig. 79) was one of the most 

 remarkable of these in having a full and continuous set of 

 teeth without any gaps, like that of the Arsinoitherium 

 already figured. 



An allied family, Oreodontidae, somewhat nearer to 

 ruminants, but with four-toed feet, were very abundant in 

 North America in Miocene times. They were remotely 

 allied to deer and camels, and were called by Dr. Leidy 

 " ruminating hogs." They seem to have occupied the place 

 of all these animals, six genera and over twenty species 

 having been described, some of which survived till the early 

 Pliocene. 



The family Palseotheridae was also abundant during the 

 same period in Europe, and less so in North America. 

 As shown in the restoration in Fig. 80, it somewhat 

 resembled the tapir; but other genera are more like horses, 

 and show a series of gradations in the feet towards those 

 of the horse-tribe, as shown by Huxley's figures reproduced 

 in my Darwinism. 



The Origin of Elephants 



Till quite recently one of the unsolved problems of 

 palaeontology was how to explain the development of the 

 Proboscidea or elephant tribe from other hoofed animals. 

 Hitherto extinct species of these huge beasts had been found 

 in a fossil state as far back as the Miocene (or Middle 

 Tertiary) in various parts of Europe, Asia, and North 

 America ; one species, the mammoth, being found ice- 

 preserved in Arctic Siberia in great quantities. Some of 

 these were somewhat larger than existing elephants, and 

 several had enormously large or strangely curved tusks ; but, 

 with the exception* of Dinotherium, which had the lower 

 jaw and tusks bent downwards, and Tetrabelodon, with 

 elongated jaws and nearly straight tusks, none were very 

 different from the living types and gave no clue to their 



