THE LIFE OF MAMMALS 
The hippos, then, are a decadent race. Their origin is un- 
known, but the Lower Pliocene formations of India contain 
fossil species, and one existed there until after the advent of 
Stone-age man. In the warm Preglacial period, Europe was 
the home of the present African form,’ and until recently 
Madagascar had a dwarf species; a still smaller existing one 
little known is the Liberian variety, only six feet long. 
The range of the hippopotamus has been greatly reduced 
by the spread of civilization in Africa. Buffon gives an account 
of its capture in the delta of the Nile in classic times; and 
De Windt says they were to be seen at Damietta in I109 A.D., 
while Burckhardt mentions seeing them at Dongola in 1819. 
At that date they abounded in all the rivers of South Africa, _ 
but now hippos are to be got only from the rivers of the Congo 
basin, in those which feed the lower Zambezi, and at the sources 
of the upper course of the Nile. 
Horses, Tapirs, and Rhinoceroses 
(The Odd-toed Ungulates — Suborder Perissodactyla) 
We now come to the horses, tapirs, rhinoceroses, and their ex- 
tinct relatives which constitute the solid-hoofed Perissodactyla. 
The most advanced, specialized, “highest” type of this sub- 
order is presented by the horses; and thanks to the fortunate 
preservation of their remains, and to the sagacity and industry 
of American paleontologists, we are able to trace and under- 
stand the history of their development with gratifying complete- 
ness. While some early forms were exhumed and described in 
France by Cuvier, early in the nineteenth century, it was not 
until Marsh, Leidy, Cope, Wortman and others, began to 
explore the Tertiary strata of our western plains, between 
1860 and 1880, that anything like a historical series connecting 
the ancestral forms with modern ones began to appear; and it 
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