346 THE AGE OF MAMMALS 



acteristie horses of the Miocene Merychippus stage, with grinding teeth of 

 intermediate length, still survive in almost equal numbers with the more 

 progressive grazing horses, Protohippus, Pliohippus, and Neohipparion. 

 The rhinoceroses are represented l^y the teleocerine and aceratherine phyla, 

 both of which reach a high degree of specialization. Of these the aceratheres 

 or hornless rhinoceroses ara represented by species of Aphelops comparable 

 in evolution to the Aceratherium blanfordi of the Pliocene of Asia as well as 

 by the short-headed Peraceras. The teleocerine rhinoceroses, which are 

 also believed to survive in the Pliocene of Asia, although extinct in Europe, 

 attain their maximum evolution and size, and are present in great number 

 and variety. The aberrant perissodactyl chalicotheres have apparently 

 disappeared in North America, though it is possible that some of these 

 animals will be unearthed by future exploration, since they are believed to 

 have survived in Asia in Pliocene times. 



Indicative of the Upper Miocene rather than of the Lower Pliocene age 

 of this fauna is the fact that the trilophodont and tetralophodont mastodons 

 still retain the long lower jaws or longirostral character of the Miocene 

 mastodons of Europe and America, whereas the Lower Pliocene mastodons 

 of Europe are referred to the short-jawed species M. arvernensis; this 

 specific reference, however, may not be correct, so that too much stress 

 should not be laid upon this single feature. 



Among the camels PUauchenia is now the characteristic genus; this is 

 a typical grazing camel with affinities to the llamas of South America, as the 

 name indicates. We also find surviving the short-limbed or grazing camel 

 Procamelus. The browsing or giraffe camel (Alticamelus) still occurs. 



In the earliest of these supposed Pliocene formations, namely, the 'Re- 

 publican River ' of Kansas and ' Alachua Clays ' of Florida, we have dis- 

 covered no evidence of the existence of the Cavicornia or hollow-horned 

 ruminants of the Old World tyi3e. The older formations, therefore, contain 

 rhinoceroses, but do not contain, apparently, the antelopes or Bovidae. 



The Alachua Clays or 'Archer Beds' of Florida 



These clays were so named by Dall in 1885.^ They had been referred 

 by some authorities to Upper Miocene, by others they had been regarded 

 as late as Pliocene or even Pleistocene. They appear on the western anti- 

 cline of the higher portions of Alachua County (Fig. 160), along the banks 

 of many rivers and streams, occurring in sinks, gullies, and other depres- 

 sions, in rocks of successive age. The clays are of a bluish or grayish color, 

 and extremely tenacious. The deposits were believed by Dr. J. C. Neal 

 (1883) to have occurred along the margins of an ancient lake, which he 

 named Lake De Soto. The existence of such a Pliocene lake or series of 



' Dall, W. H., and Harris, G. D., The Neocene of North America. Bull. U.S. Geol. Surv., 

 no. 84, 1892. 



