838 



THE AGE OF MAMMALS 



discovery ^ in the Virgin Valley, Nevada, of antelopes (Ilingoceros) with 

 spirally twisted horn cores, related to the kudus (Strepsiceros) of the tra- 

 gelaphine section, the section represented to-day by the nilgai of India, 

 as well as bush bucks and harnessed antelopes, the sitatungas, kudus, and 

 elands of Africa. There are a number of species of these twisted-horn 

 types as well as an oval-horned genus {Sphenophalos) . The type specimen 



of Ilingoceros resembles the 

 Protragelaphus of the Pliocene 

 of Europe and Asia. Thus 

 we have definite proof of the 

 existence in the Western plains 

 and mountain region in Plio- 

 cene times of considerable if 

 not of great herds of antelopes 

 of Asiatic and African type. 

 The bearing of this discovery 

 on the zoogeographic relations 

 of the New and Old Worlds 

 in the Pliocene is very signif- 

 icant. 



Extinction and chronology. 

 — The attempt to form New 

 and Old World parallels brings 

 up the question of the value 

 of extinction in determining 

 geologic time. Was there a 

 world-wide extinction of the teleocerine rhinoceroses at the close of the 

 Miocene, or did these animals survive into Pliocene times in America 

 as well as in Asia? The answer is that there is considerable but not 

 as yet conclusive evidence that the teleocerine rhinoceroses reached 

 their highest development and extension in the Lower Pliocene of America 

 and Asia. The same remark applies to the giant dogs, or amphicyons, 

 which disappear in the Upper Miocene of Europe, but are found in the 

 supposed Middle Pliocene or Blanco beds of Texas, and are also recorded 

 in the Pliocene of Asia. The clawed perissodactyls, the chalicotheres, 

 disappear in the Upper Miocene of Europe and North America, but 

 survive in Asia even into the Pleistocene, according to Schlosser.^ A great 

 number of mammals of various kinds survive in southern Asia after they 

 disappear in Europe and North America. The conclusion is that extinc- 

 tion per se is of little value in geologic synchronism. 



Fig. 158. — A recent strepsicerine antelope of Africa 

 the kudu {Strepsiceros kudu) . After Gambler Bolton, 



' Merriam, J. C, The Occurrence of Strepsicerine Antelopes in the Tertiary of North- 

 western Nevada. Univ. Cal. Publ., Bitll. Dept. Geol, Vol. V, no. 22, Doc, 1909, pp. 319-330. 



- Schlosser, M., Die fossilen Saugethiere Chinas nebst einer Odontographie der recenteu 

 Antilopen. Abh. k. bayer. Akad. Wiss., CI. II, Vol. XXII, Pt. 1, Munich, 1903. 



