CAUSES OF THE EVOLUTION AND EXTINCTION OF THE TITANOTHERES 



873 



parasite also lives in the blood of healthy rarts. Anal- 

 ogous to this is the "sleeping sickness" that affects 

 man, which has spread rapidly from west to east 

 Africa, carried by a fly, Glossina palpalis, claiming 

 hundreds of thousands of victims. 



Rinderpest in Africa. — The rinderpest or cattle 

 disease has been the greatest destroyer of the wild 

 African quadrupeds. This disease has been known 

 from time immemorial in Europe and central Asia. 

 It is believed by some to have entered the Nile 

 provinces of Africa in 1880, to have reached the 

 Transvaal in 1896, and thus to have traveled the 

 whole length of the Dark Continent. It has been 

 spread largely through the infection of wild ruminants. 

 It is fatal to the wild buffalo, Bos (Bubalus), the kudu 

 {Strepsiceros Icudu), the sable antelope {Hippotragus 

 niger), the gnu (Connochaetes albojuhafus and 0. 

 taurina), also in the Philippines to the carabao, 

 Bos (Buhalus) Icerahau. It is fatal to 90 to 100 per 

 cent of domesticated cattle. The parasite causing 

 rinderpest is undiscovered, no natural immunity is 

 known (methods of artificial immunity were dis- 

 covered in 1893), and it is distinguished by the ease 

 and rapidity with which it spreads in all countries, 

 climates, and seasons, being carried even on the clothes 

 and person of man. It therefore appears improbable 

 (Bruce, 1905.1) that insects have anything to do with 

 it. It may be due to a wind-borne bacterial organism. 



By analogy we may imagine that a disease affecting 

 the Pleistocene horses of North America may have 

 traveled an equal distance, from Texas to Patagonia, 

 and destroyed all the South American Equidae. 



Moist rhinarium and other eliminating causes in 

 Africa. — The rinderpest of 1889-1899 illustrated the 

 eliminating value of a single organ, the external 

 nostril. Rinderpest (see above) is fatal to domestic 

 cattle, to all the Bovinae and to the antelopes most 

 closely approximating to them, including the tragela- 

 phines (eland, kudu, bushbuck, reedbuck, dyker), all 

 these ruminants having a large, moist rhinarium, 

 whereas animals with a small, part hairy rhinarium — - 

 the sable antelope, roan antelope, hartebeest, impala — 

 suffered much less if at all. 



The wildebeest and hyena, although immune to 

 rinderpest, are' hosts of the nagana trypanosomes, 

 which are carried by the tsetse fly. In the region of 

 the middle Zambezi the buffalo perished in enormous 

 numbers, the remains of 200 animals being observed 

 within a few acres — piles of bones and skulls, a veri- 

 table Golgotha. Geographically the course of the 

 rinderpest was most erratic, here diverted by a range 

 of mountains, there sweeping down one bank of a 

 river and leaving the other untouched. Subsequent 

 to the rinderpest epidemic the tsetse fly was elimi- 

 nated over certain areas, especially those that had 

 been covered by the rinderpest south of the Zambezi. 

 Whether the elimination of the fly was in any way 



connected with the rinderpest is a matter of specu- 

 lation. 



As a result of the rinderpest epidemic in South 

 Africa the last of the elands disappeared and the 

 buffalo were reduced to one herd of about 20. In the 

 Sabi Bush the kudu were greatly thinned down, 

 whereas south of the Zambezi, in British Nyasaland, 

 the rinderpest made no difference whatever in the 

 status of the fly; possibly climatic conditions or some 

 parasitic enemy caused the decrease of the flies. 



Pleistocene extinction of horses. — Among all the 

 problems of Pleistocene extinction presented in 

 America that of the horses is certainly one of the most 

 difficult. These animals are far superior to cattle in 

 their adaptability to changing conditions of life and 

 in resourcefulness in severe wuiters. They were very 

 numerous in North America at the beginning of 

 Pleistocene time, whereas at the end of it they were 

 apparently extinct. Similar extinction occurred both 

 in North and South America at this period. The 

 numerous and highly specialized horses of Mexico 

 shared in this extinction, although we might have 

 regarded the high plateau of Mexico as a ready means 

 of escape from the more severe conditions in the north 

 in the glacial epoch. It has consequently been 

 suggested by Osborn (1906.287) and by others that 

 the American horses may have been swept out of 

 existence by some epidemic disease or diseases. This 

 theory has subsequently received some support 

 through the discovery by Cockerell (1907.1; 1909.1) 

 of two species of fossil tsetse fly (Glossina) very similar 

 to the African types of to-day. These flies are found 

 in the Florissant lake beds of Colorado, which are 

 regarded as of upper Miocene age, and were contem- 

 poraneous with the varied equine fauna. 



Ticlcs and horses. — Ticks, even those that bear no 

 infection, form effective barriers to the introduction 

 of quadrupeds into certain regions. In some forested 

 parts of South and Central America they endanger 

 human life. In certain regions of Africa ticks are 

 practically fatal to horses. As stated orally by Dr. 

 D. G. Elliot, thousands of ticks may gather on a horse 

 as a result of a single night's grazing. The mane 

 especially serves to collect these pests. Thus the 

 falling mane of the northern horse is distinctly dis- 

 advantageous as compared with the upright manes of 

 the asses and zebras. Ticks are capable of driving 

 certain types of animals entirely out of a country and 

 of indirectly causing certain modiflcations of the hair 

 and epidermis. 



In the forests of southern California prickly seeds 

 of certain plants find their way into the nostril sac of 

 horses and cause serious if not fatal abscesses unless 

 removed. 



Distribution of horse siclcness. — Horse sickness is 

 local in distribution, prevailing in low countries and 

 during wet seasons. The same climatic relation is 



