472 THE AGE OF MAMMALS 



Hipparion high, having at its base a Pliocene limestone 



Megatherium composed of marine shells, while the post-Plio- 



Mylodon harlani cene layer is a shallow river formation consist- 



Procyon ing of yellow sands with bands of ferruginous 



Didelphys clay four feet in thickness. 



Fiber The fossilized teeth are brown or black in 



Castor color. The remains of ancient or extinct species 



Alces of animals are mingled with those of recent spe- 



Dicotyles cies; thus the fossil tapir which occurs there, 



not distinguishable from the living T. ameri- 

 canus, is an animal also distributed in Texas, Louisiana, Kentucky, Missis- 

 sippi, Indiana, Ohio, and South Carolina. Again, the common gray 

 rabbit (Lepus sylvaticus) is associated with fragments of the teeth of the 

 great Megatherium and Mylodon. The original specific identifications are 

 very doubtful, and are therefore omitted in the table opposite. 



The species of horse found here {E. fraternus) is characteristic of the 

 southeastern United States; it represents an animal of intermediate size 

 with teeth scarcely larger than those of the domestic donkey (E. asinus), 

 and of a very complex pattern. 



Rancho La Brea, southern California (Fig. 194, 28). — In southern Cali- 

 fornia, about nine miles west of Los Angeles, is what promises to be the 

 most remarkable deposit of Pleistocene mammals thus far discovered in 

 America. As described by Merriam ^ (1906) this deposit is fifteen feet or 

 more in thickness and a quarter of a mile in extent. It is located im- 

 mediately over a sharp fold of rock, heavily impregnated Avith petroleum, 

 which, issuing to the surface, has evaporated, forming springs and pools 

 of tar which have dried and hardened locally to the consistency of asphalt. 

 It contains scattered bones in a remarkably fresh condition, and pieces of 

 partly lignitized wood. The remains are those of mammals and birds. 

 Among the latter are ducks, geese, pelicans, eagles, condors, and peacocks. 

 The smaller mammals include mice, rabbits, and squirrels; the larger are 

 represented by extinct species of coyotes, giant wolves, bear, saber-tooth 

 tigers, horses, bison, camels, mammoths, and large ground sloths. In the 

 early stages of the accumulation of the asphalt, the gummy surface appar- 

 ently acted as a, trap for unwary animals: where there were pools of water 

 the water birds of all kinds were entrapped in the soft tar about the mar- 

 gins, while the land birds and smaller mammals were ensnared in attempt- 

 ing to reach the water. The larger percentage of the birds are water forms, 

 and the larger herbivorous mammals are for the most part represented by 

 young individuals. A relatively large number of carnivorous animals cor- 

 responds with what is observed around recent asphalt pools. 



In attempting to estimate the age of this fauna we first observe the 



> Merriam, J. C, Recent Discoveries of Quaternary Mammals in Southern California. 

 Science, n. s., Vol. XXIV, no. 608, Aug. 24, 1906, pp. 248-250. 



