THE PLIOCENE OF EUROPE, ASIA, AND NORTH AMERICA 337 



Europe; the latter contain mammals which may be closely compared with 

 those of the Western plains. This coincidence is observed in the opening 

 of the Pliocene in the formation known as the 'Alachua Clays,' and again 

 in the close of the Pliocene in the ' Peace Creek ' beds, both of which mammal- 

 bearing formations have been described in relation to their surrounding 

 shell-bearing formations by the expert invertebrate palaeontologist, Dr. 

 W. H. Dall. The fauna and relations of these formations will be described 

 below. 



Relations loith Eurasia. — The mammals of the American Pliocene are 

 the least known of all the American epochs. Early in the Pliocene the 

 typical Cavicornia, or hollow-horned ruminants of Eurasia, first make their 

 appearance in North America in forms somewhat similar in appearance to 

 the Protragocerus of the Miocene of Europe. In the Upper Pliocene we 

 have seen that the camels of North America first make their appearance 

 in India and China. With these exceptions we know of no very grand or 

 marked interchanges of life between the New and Old Worlds in this period 

 until the very close, when the Old World elephants appear. 



American migration of Asiatic antelopes. — The appearance of true 

 Asiatic antelopes related to two of tlie great sections, the tragelaphine 

 and hippotragine, is one of the 

 most recently discovered and 

 profoundly impressive features 

 of Pliocene times. The first 

 certain evidence of this kind is 

 the supposed hippotragine 

 antelope N eotragocerus dis- 

 covered by Matthew and Cook 

 in western Nebraska in 1908 ' : 

 this animal is believed to be 

 related to the same group as 

 the Tragocerus of the Upper 

 Miocene of Pikermi, a group 

 now represented by some of 

 the largest and finest African 

 antelopes in the region south 

 of the Sahara, including the 

 roan antelope {Hippotragus 

 equinus), the sable antelope 

 (//. niger), the oryx, and the addax. The horn is short and straight, with 

 a round-oval cross section. 



This evidence of American invasion by true Asiatic antelopes was 

 brilliantly and amply confirmed during the summer of 1909 by Merriam's 



1 Matthew, W. D., and Cook, H. J., A Pliocene Fauna from Western Nebraska. Bull. 

 Amer. Mus. Nat. Hist., Vol. XXVI, no. 27, 1909. 

 Z 



By IJi-rnii-Moii ol UieiNcw \ork ZooioL'icrtl .society. 



Fig. 157. — A recent hippotragine type of Africa, the 

 sable antelope {Hippotragus niger). 



