Mammoth construction of the Great Pyramid of ancient Egypt. The earliest known proboscideans, the clade that contains the elephants, existed about 55 million years ago around the Tethys Sea area. The closest relatives of the Proboscidea are the sirenians and the hyraxes. The family Elephantidae is known to have existed six million years ago in Africa, and includes the living elephants and the mammoths. Among many now extinct clades, the mastodon is only a distant relative of the mammoths, and part of the separate Mammutidae family, which diverged 25 million years before the mammoths evolved. The following cladogram shows the placement
Mastodon incognitum "mastodon". The name "mastodon" (or "mastodont") means "breast tooth" (Ancient Greek: μαστός "breast" and ὀδούς, "tooth"), and was assigned by the French naturalist Georges Cuvier in 1817, for the nipple-like projections on the crowns of its molars. "Mastodon" as a genus name is obsolete; the valid name is "Mammut", a name that preceded Cuvier's description, making "Mastodon" a junior synonym. The change was met with resistance, and authors sometimes applied ""Mastodon"" as an informal name; consequently it became the common term for members of the genus. Species include: Since a tentative 1977 report of "M. matthewi" in China, there