MAMMOTHS AM) MASr(f/)()\S 15 



the tusk socki^ts inncli licaxicr and longer. Tlic hisks in I lie male aic six 

 to right iiu'hos ill diainotcr and six to oi<i,Iit Icct or more in Iciiglli. Tlic 

 tusks of [\\v tViiudo air only tlinv or four iiiclics in dianiclcr and loin- to six 

 feet in lenj^th. Tlic urine ling' tcrtli arc nnicli alike. 'I'licrc arc no tusks 

 in tlio lower jaw of the female mastodon, hut in the adult male there is 

 frequently a pair of small |)e<;-like vestigial tusks, sometimes only one. 

 These fall out in old individuals and the socket closes up; sometimes they 

 are not i)resent in young adult males. \^u'ious specimens in the wall case 

 illustrate the presence or al)sence of lower tusks in the two sexes. Of the 

 two skulls in separate case the larger is the AsJiley skull found near Ashley, 

 Indiana, in 1900; the smaller is the Fulton sJxidl found near Fulton, Indiana, 

 in 1915. A fine palate with tusks, two pair of lower jaws, sei)arate tusks 

 and parts of skeleton were found with the Fulton skull and are shown in the 

 wall case. All belong to females of different ages, the complete skull being 

 the oldest. 



Distribution of the Mastodon. The American mastodon ranged all 

 over the United States and Canada, and has been found in Alaska, Siberia 

 and as far east as central Russia (Podolsk). In the wall case are shown 

 specimens from Florida, Georgia and South Carolina illustrating its south- 

 ern distribution, from Kansas, Texas and southern California, illustrating its 

 western and southwestern occurrence, from Point Barrow, Alaska (col- 

 lected by Vilhjalmar Stefansson), showing its northern range, casts of teeth 

 from Russia to show^ its occurrence in the Old World. The closely allied 

 species, M. borsoni is recorded from numerous localities in eastern Europe 

 and Siberia. 



IV. THE LATER TERTIARY MASTODONS. 

 Genera Dibelodon, Rhyncotherium, Tetralophodon, Trilophodon. 



MIOCENE and Pliocene with some survivors in the Pleistocene 

 (Glacial) epoch. 

 These proboscideans preceded the elephants and great mastodons 

 of the age of man. They are of smaller size and include quite a variety of 

 different types, some of which, in the Old World, are believed to be an- 

 cestral to the elephants (through Stegodon, see p. 24), while others prob- 

 ably gave rise to the American Mastodon. Most of the Tertiary 

 mastodons, however, are more or less clearly off the direct line of 

 descent, and their exact phylogeny is not yet certainly known. We will 

 point out here only the general relations and distribution of the different 

 types, so far as know^n. 



The Two-tusked Mastodon. 

 Genus Dibelodon {=Stegomastodon) . Pliocene of North America, 



