1() AMj:iiI( A\ Ml'SEl'M (HIDE LEAFLETS 



with a few survivors in llio PltMstocoiic. CliicHy Plcistocoiic in South 

 Auicrica, with a few j)r('curs()rs iu hitc IMioccnc. 



IpixT tusks iar^c, up-curved or strai^lit, with or without enauiel 

 l)au(l. Lower tusks vestigial or absent (usually absent). Cheek teeth 

 shoit -crowned, tlie anterior molars falling- out early in life, so tliat the 

 younji, adult retains two and old indi\'iduals only one molar. The second 

 molar has three cross crests, the last fi\e to eight. 'I'he crests are not clearly 

 defined as in the American Mastodon, hut composed of a pair of conical 

 cus|)s with a mnn))er of smaller cusps interposed, arranged in a trefoil 

 pattern, so tliat the valleys between the crests are l)locked in the middle 

 instead of running clear across as in the later form. This is tlie primitive 

 form among the nuistodons, and aj)j)ears in most of tlie Tertiary types 

 with \ariations in the number and arrangement of the minor cusps, grouped 

 customarily into the "single trefoil" and "doul)le trefoil" type. 



This genus therefore is a derivative of the primitive mastodon type 

 (Trilophodou) of the Miocene, paralleUng the elephant phylum in 

 (1) loss of lower tusks and shortening of the jaw, (2) increase in 

 size of the upper tusks with tendency to upward curvature and loss of 

 enamel band, (3) reduction in the number of functional teeth, the last 

 molar becoming the principal grinder. 



The typical form is D. mirificua Leidy, the characteristic species 

 of the Pliocene of North America, well represented by the fine skull and 

 jaws and several other specimens from the Blanco formation of Texas, 

 showing different stages of wear in the teeth. All the South American 

 mastodons belong to this genus. They are chiefly from the Pleistocene 

 formations ranging from Columbia to Argentina, but some may be as old 

 as the late Pliocene. 



The Long-jawed Mastodon Tetralophodon. This group of Tertiary 

 mastodons is notable for the great elongation of the jaws in some species. 

 The })owerful upper and lower tusks are but little curved and directed 

 forward. The enamel bands are ])reserved on both. The species are 

 readily distinguished })y the second molar which has four crests instead of 

 three; otherwise the grinding teeth are much like those of Dibelodon 

 but the anterior molars retained longer in use. It is characteristic 

 of the ri)per Miocene and early Pliocene of Europe, Asia and 

 North America. The typical forms are 7\ lofu/irostris and (wrenictisis, 

 of Europe, and in this country T. campcstcr, of which the type is shown in 

 the wall case. In 7\ ar re men. sis the jaw is comparatively short with small 

 lower tusks. Casts of jaws of the European species are exhibited in the 

 wall case. 



The Beaked Mastodon Rhyncotherium. In this genus the upper 

 tusks are also stout, little curved and with enamel bands, but the 



