SUCCESSIVE MAMMALIAN FAUNAS 255 



The hoofed mammals were present in fairly bewildering 

 variety, but were restricted to the two orders of the Perisso- 

 dactyla and Artiodactyla. The Perissodactyla, while they 

 no longer had the relatively dominant position which they 

 held in the middle Eocene (see p. 270), had suffered no actual 

 loss ; and no less than seven famihes of them, or six by another 

 scheme of classification, had members in the North America 

 of White River times, a very notable difference from the 

 present order of things, when there are but three families in 

 the entire world, none of which enters North America. The 

 Eocene family of the ftitanotheres became extinct at the end 

 of the lower substage of the White River, but in that substage 

 there was a marvellous abundance of these huge beasts, some 

 of which were of almost elephantine stature and bulk. The 

 pair of great bony, horn-like protuberances on the nose varied 

 much in size and form in the different species, short to very 

 long, triangular, cylindrical, flattened and shovel-shaped, 

 and gave these ungainly creatures somewhat the appearance 

 of strange and very large rhinoceroses. The ftitanotheres 

 were a typically North American family, but sent migrants 

 to the Old World, at least two species reaching southeastern 

 Europe. Rhinoceroses too were extremely numerous and 

 diversified throughout the stage and are very plainly divisible 

 into three strongly contrasted series, which are sometimes 

 regarded as three subdivisions of the same family and some- 

 times put into two separate families. One of these series, the 

 fhyracodonts {^Hyracodon) , was composed of small, long- 

 necked and long-legged, slender and lightly built, cursorial 

 animals, but with short, heavy heads, which gave them a 

 somewhat clumsy look ; having neither horns nor tusks, they 

 were entirely defenceless and depended for their safety upon 

 speed alone. The second series, or famynodonts {]Met- 

 amynodon), formed the very antithesis of the first, — large, 

 heavy, short-necked, and short-legged and probably amphibi- 

 ous in manner of life, they were armed with formidable 



