NEW WORLD PALEO-INDIAN—ROBERTS 427 
Arizona, and probably from there into northwestern Mexico. The 
latter movement may have continued along the strip of coast west 
of the Sierra Madre Occidental, while the groups from the eastern 
division who proceeded southward presumably traversed the plateau 
between the Sierra Madre Oriental and the Sierra Madre Occidental. 
Eventually descendants from both must have passed through the 
Middle American funnel and into South America, where some pos- 
sibly spread along the Venezuelan Andes and into the plains of the 
Orinoco and others continued southward along the Andes to southern 
Bolivia, where they scattered southeastward across the Gran Chaco 
into Brazil, south of the Amazonian Forest, and on south into Argen- 
tina. Some may have crossed the range to the west and emerged in 
the coastal belt south of the Atacama Desert (Sauer, 1944, pp. 558-559). 
The major movements that provided most of the Indian populations, 
however, appear not to have developed until later when the Recent 
period was well established. Such accretions as may have come by 
sea were too late to affect the older groups and too small to play much 
part in the later developments. 
Although in many cases they apparently outlived the geologic 
Pleistocene, many of the animals killed by the early peoples consti- 
tute what are usually considered Pleistocene forms. They seem to 
have survived through the transition to Recent times and then to 
have become extinct rather suddenly. Causes of this widespread and 
rapid disappearance are not known. That the Paleo-Indians may 
have been a contributing factor through slaughter of the animals and 
the introduction of diseases to which they were particularly suscep- 
tible has been suggested. Other phenomena, no doubt, were also in- 
volved, and future work may produce the information necessary to 
a solution of this interesting phase of the problem. In this group of 
mammals in North America were: mastodonts, mammoths, ground 
sloths, horses, camels, and tapirs, from families now extinct; antilo- 
caprid, the giant beaver, the short-faced bear, saber-tooth cat, giant 
cat, musk ox, and bison, from genera and species now extinct but from 
families still persisting. In South America those from extinct fami- 
lies were: ground sloths, glyptodonts, “Bunomastodonts,” horses from 
the short-legged type derived from the late Pliocene immigrant, and 
the Pleistocene H'guus; while extinct genera and species from per- 
sisting families are represented by an armadillo, the short-faced bear, 
and saber-tooth cat (Colbert, 1942). The early inhabitants of both 
North and South America probably were contemporaneous with other 
animal forms, but their remains either have not been found in direct 
association or the association was too doubtful to receive consideration. 
Since many of these animals seem to have become extinct at a rela- 
tively recent date, associations between their bones and artifacts do 
