mastodon, name for a number of prehistoric mammals of the extinct genus Mammut, from which modern elephants are believed to have developed. The earliest known forms lived in the Oligocene epoch in Africa. These were long-jawed mastodons about 41/2 ft (137 cm) high, with four tusks and a greatly elongated face. Their descendants in the Miocene epoch were the size of large elephants, the latest forms having long, flexible trunks, like those of elephants, and only two tusks. During Miocene times they spread over Europe, Asia, and North America. The mastodons were forest dwellers; they obtained their food by browsing and their teeth were more numerous and of a simpler form than those of the elephant. They were apparently extinct in the Old World by the early Pleistocene epoch but survived in North America until late Pleistocene times. They are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Proboscidae, family Mammutidae.

Any of several extinct elephant species (genus Mastodon) that lived worldwide 23.7 million–10,000 years ago or later in North America, where they were contemporaneous with historic American Indian groups. Well-preserved remains are quite common. Mastodons ate leaves and had small grinding teeth and long, parallel, upward-curving upper tusks; males also had short lower tusks. Shorter than modern elephants, they had long, heavily built bodies and short, pillarlike legs. Their long hair was reddish brown. The skull was similar to that of modern elephants but lower and flatter, and the ears were small. Human hunting may have played a role in the mastodon's extinction. Seealso mammoth.

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