3 68 



THE SONORAN REGION. 



[CHAP. 



to the westward of the Mississippi. Possibly a small deer-like 

 animal from the Tertiaries of the same area known as Cosoryx, 

 may have been the ancestral stock of the prongbuck. Lastly, the 

 peccaries (Dicotyles), which are now chiefly South American, appear 

 to have been originally Sonoran types which have migrated south- 

 wards ; their fossil remains being common in the Tertiaries of the 

 United States, whereas they are unknown in South America before 



FlG. 75. HEAD OF MALE MULE-DEER (Cariacus macrotis). 



the Plistocene. Their near affinity to the earlier Tertiary pigs of 

 the Old World indicates that at a more remote date they spread 

 from a more northerly starting-point. 



With regard to the armadillo (Tatusia) found in the Sonoran, 

 this is clearly a very recent immigrant from the Neogseic realm ; 

 and although opossums (Didelphys) were abundant in North 

 America during the early portion of the Tertiary epoch, it is not 

 improbable that the same explanation will hold good for their 

 existing Sonoran representatives. 



