Stegomastodon (Greek for "roof nippled tooth"); pronounced STEG-oh-MAST-oh-don
Plains of North and South America
Late Pliocene-Modern (three million-10,000 years ago)
Size and Weight:
About 12 feet long and 2-3 tons
Moderate size; long, upward-curving tusks; complex cheek teeth
Its name sounds impressive-like a cross between a Stegosaurus and a Mastodon-but you might be disappointed to learn that Stegomastodon is actually Greek for "roof-nippled tooth," and that this prehistoric elephant wasn't even a true Mastodon, being more closely related to Gomphotherium than to the genus to which all Mastodons belonged, Mammut. (We won't even mention Stegodon, another elephant family to which Stegomastodon was only distantly related.) As you may already have guessed, Stegomastodon was named after its unusually complex cheek teeth, which allowed it to eat such un-pachyderm-like foods as grass.
More importantly, Stegomastodon is one of the few ancestral elephants (besides Cuvieronius) to have prospered in South America, where it survived until historical times. These two pachyderm genera made their way south during the Great American Interchange, three million years ago, when the Panamanian isthmus rose up from the seafloor and connected North and South America (and thus allowed the native fauna to migrate in both directions, with sometimes deleterious effects on native populations). To judge by the fossil evidence, Stegomastodon populated the grasslands east of the Andes mountains, while Cuvieronius preferred higher, cooler altitudes.
Given that it survived until shortly after the last Ice Age, 10,000 years ago, it's almost certain that Stegomastodon was preyed on by the indigenous human tribes of South America-which, along with inexorable climate change, drove this pachyderm to complete extinction.