Mastodon, common name for any of the extinct elephantlike mammals that constituted the family Mammutidae of the order Proboscidea (“long snouted”). The leaf-eating mastodons were widely distributed in the forests of the world from Oligocene to Pleistocene times. Their remains have been found in North America, Africa, Europe, and Asia, and are often remarkably well preserved. Like the modern elephant, the mastodon was very large, with thick, sturdy legs; a huge head; tusks; and a flexible, muscular trunk. Like the mammoth, the mastodon was covered with shaggy hair. The animals differed from elephants and mammoths, however, in having complete tuberculate teeth. Their upper tusks were long and curved backwards; they had transverse crests on their grinding teeth. Mammut americanum, almost the size of a modern Indian elephant, was common throughout what is now the United States; it did not become extinct until about 8000 years ago.