866 



TITAN0THERE3 OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



Influence of drougJits in central Africa. — The in- 

 fluence of the gradual decrease of moisture in a country 

 is clearly illustrated in the conditions which prevail in 

 the African Continent to-day, as observed by Gregory, 

 Foa, and Schillings. Thirst, like hunger, first drives 

 quadrupeds to take extreme risks, which they would 

 absolutely avoid during natural conditions. The 

 drinking places or water pools during long seasons of 

 drought become fewer in number and more widely 

 separated, and large animals driven to them by thirst 

 are more readily attacked and killed by Carnivora. 

 The pools become separated by distances of 30 or 40 

 miles, thus necessitating long excursions to and from 



that the central Sahara was once by no means the 

 desert it is now. North of the Sahara — that is, along 

 the Mediterranean coast of Africa — there is evidence 

 of profound changes in climate during and since 

 Pleistocene time. In Pleistocene time this region was 

 still distinctively a part of the African or Ethiopian 

 region. After upper Pliocene time this region enjoyed 

 a warm temperate climate characterized by abruptly 

 alternating dry and rainy seasons; there is evidence of 

 periods of excessive rainfall at the beginning of the 

 Pleistocene epoch. Various indications point to in- 

 creasingly long periods of drought and progressive 

 secular desiccation of this great region as the Pleisto- 



FiGURE 759. — Influence of secular desiccation on the archaic and modern orders of mammals 



the feeding places, during which the quadrupeds are 

 exposed to attack. Finally some of the pools dry 

 up entirely and, as J. W. Gregory observes (1896.1, 

 p. 268): "Here and there around a water hole we 

 found acres of ground white with the bones of rhinoc- 

 •eroses and zebra, gazelle and antelope, jackal and 

 hyena, * * * all the bones were there fresh and 

 ungnawed." These animals, which had not migrated, 

 liad "crowded around the dwindling pools and fought 

 for the last drops of water." Such perishing of 

 animals in great numbers from thirst would bring 

 about diminished herds, spoken of above as the final 

 ■cause of extinction through inability to protect the 

 joung. 



Pleistocene desiccation oj northern Africa. — There are 

 archeological and even historical proofs (Herodotus) 



cene advanced, resulting in the partial extinction and 

 partial migration of the great equatorial quadruped 

 life to central and southern Africa (Pomel, 1895.1). 

 Thus the elephants, rhinoceroses, hippopotami, and 

 giraffes disappeared. A typical African fauna was 

 replaced by an equally typical European fauna, which 

 included the bear and the deer. 



Desiccation and extinction in central Australia. — • 

 Wallace's opinions as to the causes of the extinction 

 of animals in Australia have been cited more as to the 

 effect of the conditions during the glacial epoch and to 

 continental contraction in general than as to the special 

 causes of extinction in Australia. More recent re- 

 search, set forth by the geologist Tate (1889.1) and 

 the zoologists Hedley (1894.1) and Baldwin Spencer 

 (1896.1), shows that in Pliocene time heavy rainfall or 



