PLEISTOCENE OF EUROPE, NORTH AFRICA, AND NORTH AMERICA 481 



annular structure of the dentine appears to indicate (Osborn, 1908) that 

 the growth was intermittent; an animal with tusks eight feet in length 

 exliibits twenty-four of these growth rings, which may be interpreted as 

 proving that it attained an age of more than twenty-four years. The in- 

 dications are that mastodons were extraordinarily abundant; it is estimated 

 by Clarke that they may have been at one time as numerous as the bison. At 



Fig. 211. — The Bison in Pleistocene times. Localities from which principal types and 

 other specimens of fossil bison have been recorded. Authority of F. A. Lucas. 1. Bison 

 bison. 2. Bison occidentnlis. 3 Bison antiquus. 4. Bison crassicornis. 5. Bison alleni. 

 6. Bison fer ox. 7. Bison latifrons. 



Big Bone Lick, Kentucky, remains of mastodons far outnumber those of the 

 Columbian mammoth, being five times as numerous as those of the mam- 

 moth and a hundred times as numerous as those of the bison. If these 

 animals were contemporaneous with man in post-Glacial times, it is possible 

 that they may have been hunted or driven to extinction through his agency. 

 2i 



