PLEISTOCENE ECOLOGY AND BIOGEOGRAPHY 403 



than earlier in the Pleistocene and (2) that extinction is not related 

 to the Glacial period or to the climatic change brought on by 

 glaciation. 



In part such figures may be an artifact of paleontological sampling. 

 Late Pleistocene sediments, bogs, caves, and alluvium, are better 

 preserved than older deposits exposed to a longer history of geo- 

 logical wear and tear. The late Pleistocene should be better known 

 than a preceding fauna. Nevertheless, accepting the fossil record at 

 face value, it seems that extinction was predominantly a Wisconsin 

 phenomenon. The facts do not agree with the proposal that the rise 

 in Pleistocene extinction rates is the result of climatic change. 



Late Pleistocene Extinction Affected Only Large Animals 



Obviously, this is not strictly true, as Eisley (1946) and Gill (1955) 

 pointed out. On the one hand, cetaceans and pinnipeds were unaf- 

 fected; on the other, small to medium-sized West Indian mammals, 

 lizards, and birds disappeared. In tropical forests and savannas 

 certain edentates survive, such as the anteaters and tree sloths. 

 Their plains-dwelling relatives of subequal size, such as Nothro- 

 therium and Chalmytherium, disappeared. Moose, elk, white-tailed 

 deer, and probably bison survived in temperate forests while, except 

 for one species of pronghorn and the mule deer, the grasslands were 

 stripped of large herbivores. 



Nevertheless, the size relationship is crucially important. The 

 vulnerability on most islands of relatively small animals (from the 

 size of a Norway rat to that of a beaver) can be contrasted with 

 that on continental areas where, aside from possible trimming of 

 marginal populations, the extinction of such small animals did not 

 occur at the end of the Pleistocene. I am indebted to K. C. Parkes 

 for pointing out that, of the reasonably rich late Pleistocene passerine 

 avifauna, there are recognized only two extinct genera, both in the 

 family Icteridae and both cowbirds, Pandanaris and Pyelorhamphus 

 (Wetmore, 1956). It requires no great imagination to suggest that 

 they shared a commensal table with the modern cowbird genera, 

 Molothrus and Tangavius, and that extinction of the large herbivores 

 reduced the variety of ecological niches for both scavenger and 

 cowbird life forms. The extinct scavengers are more numerous and 

 include the genera Breagyps, Teratornis, Cathartornis, Neogyps, and 

 Neophrontops. 



