1919] Mcrriam: Tertiary Mammalian Faunas of Mohave Desert 451 



Stage of Evolution and Relationships of the Barstow Fauna 



relation to tertiary faunas of the great basin region 

 The fauna of the Barstow beds represents a stage in the evolution 

 of Tertiary mammalian faunas not previously distinctly recognized in 

 the Great Basin Province. It seems clearly later than the Middle 

 Miocene stage of the Mascall and Virgin Valley ; and is markedly 

 older than Rattlesnake, Thousand Creek, and Ricardo, representing the 

 next known stage following the Middle Miocene in the Great Basin. 

 The fauna of the Barstow has few if any species in common with 

 that of the Ricardo, and is of a distinctly older type. Its nearest 

 relationships are with the faunal assemblage of the Cedar Mountain 

 region of southwestern Nevada, from which it possibly differs some- 

 what in stage. 



Compared with the Middle Miocene faunas of the Mascall and 

 Virgin Valley the Carnivora of the Barstow fauna show a more pro- 

 gressive stage. Large aelurodons are common, though Tephrocyon, 

 a characteristic genus of the Great Basin Middle Miocene, is also well 

 represented. Aehirodon is only doubtfully represented in the Middle 

 Miocene. Among the ungulates Hypohippus is represented by a 

 larger species than that of the Virgin Valley. The abundantly rep- 

 resented Merychippus is of a larger type, with longer-crowned cheek- 

 teeth than that of the Mascall and Virgin Valley, and grades into 

 forms which are difficult to exclude from Protohippus. Though such 

 advanced forms as Pliohippus and Hipparion are reported from the 

 Mascall no remains of either of these genera are certainly known from 

 that formation. Some of the species previously listed from the Mascall 

 have been obtained in the Rattlesnake by University of California 

 parties. In the Virgin Valley beds, with a fauna similar to that of 

 the Mascall, there is no suggestion of the presence of Equidae more 

 advanced than Merychippus. 



The Dromomeryx of the Barstow seems somewhat more advanced 

 and less common than that of the Mascall and Virgin Valley. Mery- 

 coclus, which is abundantly represented in the Barstow, is less common 

 and less advanced in the Virgin Valley, and is unknown as yet in 

 the Mascall. The relatively primitive Blastomeryx is well known in 

 the Virgin Valley, but not found in the Barstow. Blastomeryx has 

 not been reported from the Mascall up to this time. 



Rhinoceroses are unknown in the Barstow, but this peculiarity of 

 the fauna may be due to local conditions rather than to stage of 

 development of the fauna. 



