EXTINCT FAUNAS OF THE MOHAVE DESERT 259 



North American stock. 'No types from which Hipparion might presum- 

 ably be immediately derived by evolution are known in the Old World 

 formations of the period just anterior to that in which Hippanon first 

 appears, whereas in North America stages of evolution leading toward 

 Hipparion are found in formations representing the period preceding 

 the birth of this genus. So far as the writer's observations have been 

 carried, an evolutionary sequence leading to the genus, Hipparion is 

 nowhere more clearly suggested than in the relation of the Hipparion 

 of Eicardo to the Hipparion-like Merychippns of the Barstow Miocene. 

 It seems not improbable that the Old World Hipparion is derived from 

 a West- American form near the Barstow Merychippns. 



Living in the same region with the Hipparion in Eicardo time were 

 at least two other types of horses of an advanced stage referred to the 

 genus Pliohippiis. The animals of these species were nearly as large as 

 the smaller forms of the modem domestic horse. Their teeth were long- 

 crowned and well adapted to grazing as in existing forms, but their 

 feet still bore small side-toes somewhat as in Merychippns of the 

 Barstow. The pattern of their teeth is quite unlike that of the Hip- 

 parion and considerable differences separate them in skeletal structure. 

 They presumably occupied a different niche in the organization of 

 the fauna, but what it was is not entirely clear. 



In the Eicardo fauna, as at Barstow, we find a rare oreodon, the last 

 representative of this important family known west of the Wasatch. 

 The Eicardo type follows the rule in being more specialized than that 

 in the Barstow Upper Miocene. Little deer-antelope much like those 

 of Barstow are also known by the last representatives in the Great 

 Basin. Eodents are rare. The mastodon group is still represented 

 by animals with four tusks, a pair being present in the lower jaw as well 

 as one in the upper jaw. 



Of the camels there are several species known from Eicardo. They 

 represent genera similar to those in the Barstow Miocene, but are gen- 

 erally of larger type, and are presumably in a large part specifically 

 different. Carnivores are relatively abundant. Large heavy-headed 

 selurodons like those of Barstow are present, but possibly all belong to 

 new species. With these are other forms of the same group, but larger 

 and stronger. There is a marten of a new species. Of the cats, one is a 

 saber-tooth of a rare type somewhat similar to a species known in India. 

 One specimen, belonging to a gigantic animal of the Felis or true cat 

 type, was at least as large as a male African lion of the present day. 

 Another specimen is from a smaller cat possibly like a puma. 



Large tortoises are known in the Eicardo, as at Barstow. At least 

 one form seems to differ in its character from the Barstow species. 



In the table on page 262 a comparison of the Eicardo and Barstow 

 faunas would show almost complete specific separation of the life stages. 



