PLEISTOCENE ECOLOGY AND BIOGEOGRAPHY 405 



bara, dire wolf, short-faced bear, smilodon, ground sloths, glypto- 

 donts, horses, a tapir, extinct peccaries, camels, mastodons, mam- 

 moths, and various small mammals conspecific with living species 

 (Cooke, 1945, pp. 308-309). Forty years of scrutiny have not re- 

 solved the apparent contradiction that a rich and varied extinct 

 savanna fauna survived here until a very late date, perhaps 4,000 to 

 2,000 years ago, contemporaneous with archaic man (Rouse, 1952; 

 Heizer and Cook, 1952). 



In South America an extinct mastodon, Ciivieronius, was found 

 associated with pottery (Spillmann in Osborn, 1936, pp. 571-574). 

 More recently a radiocarbon sample from Minas Gerais, 3,000 ± 

 300 B.P. (M-354), "... should date the age of the extinct Giant 

 Bear" (genus unspecified, collected by Evans and reported in Crane, 

 1956, p. 672). The recent review of mastodon remains and radio- 

 carbon dates by Williams (1957) indicates that outside Florida the 

 genus endured in eastern North America until at least 6,000 years 

 ago and is associated with archaic artifacts. 



One waits with keen anticipation additional study of these and 

 other problem areas such as the West Indies. Tentative conclusions, 

 based on the harvest of eight years of radiocarbon dates associated 

 with extinct animals, follow: (1) Mexican and Alaskan large mam- 

 mals were the first to be eliminated, this in Late-glacial time; 

 (2) the Plains Megafauna disappeared in the early part of the Post- 

 glacial period; (3) eastern temperate forest and tropical rainforests 

 were the last continental refugia for large mammals; (4) the Floridian 

 savanna, surrounded by forest, served as a refuge for plains her- 

 bivores after they had disappeared elsewhere in western North 

 America. 



A LATE PLEISTOCENE EXTINCTION MODEL 



An idealized descriptive model designed to illustrate probability 

 of extinction within the late Pleistocene terrestrial fauna would in- 

 clude many factors. Without doing violence to such a model we may 

 be able to limit it to three: (1) body size, (2) habitat, and (3) total 

 range of the species. Reasons for this choice and certain apparent 

 exceptions to the model will become evident subsequently. 



The probability of extinction in the late Pleistocene appears to 

 have been maximized by large body size, usually accompanied by 

 low values of r (intrinsic rate of increase), and T (mean generation 



