4o8 



MAMMALIA 



Cattle Hybrids.— One of the oldest of the cattle hybrids has been 

 that with the I^ison, or " buffalo." (Figure 232.) Potent " cattalo " 

 males are rarely produced and there is a relatively low percentage of 

 fertility among the hybrid cows. In the Dominion of Canada, Gal- 

 way cattle have been successfully hybridized with yaks in an attempt 

 to produce a stock even more cold-resistant than the hardy Irish 

 breed. Zebu-cattle hybrids, developed in Louisiana, Texas, and 

 South America, are important additions to the breeds of beef cattle 

 since they are disease resistant. The hybrid male is not fertile. 



Fig. 232. Cattalo at Wainwright, Canada. (Photo courtesy of Canadian National 



Railways.) 



Fossil Relatives of the Ungulata. — In the lowest Eocene the fossil 

 ancestors of the clawed mammals (Unguiculata) are very much like 

 those with hoofs (Ungulata). Both are five-toed, flat-footed forms 

 with freely movable fore limbs. One of the most primitive forms 

 which occurred in the lower Eocene (Phenacodus) reached the size 

 of a large sheep. In North America the mastodon {Mammut 

 americanum) appeared in the Pleistocene. The mammoth {Elephas 

 primigenius), a form whose height was usually less than nine feet, 

 appears in the Arctic ice of Northern Siberia. The Imperial ele- 

 phant (£. imperator) reached a height of over thirteen feet. The 



