672 HISTORICAL GEOLOGY 



Matthew, W. D., — The Ancestry of the Edentates: Am. Museum Jour., Vol. 12, 



1912, pp. 300-303. 

 Matthew, W. D., — The Ground Sloth Group: Am. Museum Jour., Vol. n, 191 1, pp. 



113-119. 

 Scott, W. B., — A History of Land Mammals in the Western Hemisphere, pp. 598-625. 



Pleistocene Carnivores. — One of the most characteristic animals of 

 the early Pleistocene was the saber-toothed tiger (Figs. 576, 580) 

 (Machairodus), so named because of the enormously developed, sharp- 

 edged, upper canine teeth which in some species extended 10 inches 

 beyond the jaw. An examination shows that if the jaw were 



constructed like that of other 

 carnivores, a time would come in 

 the evolution of the great canine 

 teeth when biting would be im- 

 possible. A more careful study 

 of the jaws, however, reveals the 

 fact that the lower jaw could be 



^ r> • r l dropped straight down, thus per- 



tic 580. — Restoration of a saber- ... r 



toothed tiger. (Modified after Scott.) mitting the animal to use the full 



length of its teeth in stabbing its 

 prey. The tribe has had a long history, small ancestral forms with 

 moderate canine teeth being known from the Oligocene. 



Although perhaps the most powerful of the carnivorous animals of 

 the Pliocene and Pleistocene, they nevertheless became extinct early 

 in the Pleistocene in Europe, and disappeared from the New World 

 before the close of the epoch, their place being taken by existing carni- 

 vores, such as the lion, tiger, and leopard. 



REFERENCE FOR CARNIVORES 

 Scott, W. B., — A History of Land Mammals in the Western Hemisphere, pp. 530-536. 



Horses, Camels, etc. — Horses roamed over the plains of North 

 America in great herds and were of great variety, but became fewer 

 and fewer until all had disappeared before the close of the Glacial 

 Period. Some {Equus giganteus) had teeth exceeding in size those 

 of the largest modern horses, while others {Equus tau) were more 

 diminutive than any other true horses living or extinct. 



True camels, as well as llamas, were abundant in portions of the 

 United States in the early Pleistocene, living at least as far north in 

 the United States as Nebraska (Hay Springs) and within the Arctic 



