In 1817 Cuvier named the "incognitum" "Mastodon". Cuvier assigned the name "mastodon" (or "mastodont") - meaning "breast tooth" (Ancient Greek: μαστός "breast" and ὀδούς, "tooth"), - for the nipple-like projections on the crowns of the molars. "Mastodon" as a genus name is obsolete; the valid name is "Mammut", as that name preceded Cuvier's description, making "Mastodon" a junior synonym.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 have been no reports of currently recognized "Mammut" species outside of North America according to Paleobiology database (which does not recognize "M. borsoni"). However, the status of "Mammut" or "Zygolophodon borsoni" in the literature appears equivocal. "Mammut" is a genus of the extinct family Mammutidae, related to the proboscidean family Elephantidae (mammoths and elephants), from which it originally diverged approximately 27 million years ago. The following cladogram shows the placement of the American mastodon among other proboscideans, based on hyoid characteristics: Over the years, several fossils from localities in North America, Africa and Asia have been attributed to "Mammut", but only the North American remains have been named and described, one of them being "M. furlongi", named from remains found in the Juntura Formation of Oregon, dating from the late Miocene. However, it is no longer considered valid, leaving only five valid species. A complete mtDNA sequence has been obtained from the tooth of an "M. americanum" skeleton found in permafrost in northern Alaska. The remains are thought to be 50,000 to 130,000 years old. This sequence has been used as an outgroup to refine divergence dates in the evolution of the Elephantidae. The rate of mtDNA sequence change in proboscideans was found to be significantly lower than in primates. Modern reconstructions based on partial and skeletal remains reveal that mastodons were very similar in appearance to elephants and, to a lesser degree, mammoths, though not closely related to either one.