Specialized species like Mastodon americanus have completely lost the rudimentary premolars.
Examination will, however, show that a modification similar to that which has transformed the comparatively simple molar tooth of the mastodon into the extremely complex grinder of the Indian elephant has served to change the tooth of the common pig into that of Phacochoerus.
Threeridged and four-ridged types occur both in Mastodon and Tetrabelodon.
On the other hand, in the short-chinned mastodons, as represented by the Pleistocene North American Mastodon americanus and the Pliocene European M.
They include the mandible of a mastodon and a portion of a vertebra of a large fish, both found in the Lower Madison Valley; the skull and other parts of a dog (Mesocyon drummondanus), found near Drummond, Granite county; the skull of a Poatrephes paludicola, found near New Chicago,.
At Doveholes the Pleiocene Mastodon has been reported.