Lower jaw of a straight-tusked mastodon

Lower jaw of a straight-tusked mastodon

NMMNH P-27395

Straight-tusked mastodon

Probioscidean (elephant relative)

Belen, Valencia County

Pliocene, about 2 million years ago

Pair of lower jaws

Stegomastodon was a gomphothere or mastodon with rather straight to slightly curved upper tusks, lacked lower tusks, and had 3rd molars with complicated enamel and extra plates or lophs. Tall teeth (hypsodont) with complicated enamel suggests that Stegomastodon was a grazer that fed on coarse vegetation such as grasses, compared to other contemporary gomphotheres and mastodons with simple, low-crowned teeth that were better suited for browsing on soft vegetation such as leaves. Stegomastodon disappeared in the early part of the Pleistocene epoch about 1 million years ago, shortly after the first appearance of mammoths in North America. Stegomastodon may have become extinct because it lost out in the competition with mammoths, which were highly efficient grazers on coarse grasses, having extremely tall teeth with numerous plates composed of complexly folded enamel.