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Temporal range: Late Miocene - Late Pleistocene, 5.3–0.011 Ma
|Mounted M. americanum skeleton (the "Warren mastodon"), AMNH|
|The inferred range of Mammut (Eurasian range includes that of Zygolophodon borsoni, whose genus assignment is uncertain, and M. matthewi)|
Mastodons (Greek: μαστός "breast" and ὀδούς, "tooth") are any species of extinct mammutid proboscideans in the genus Mammut, distantly related to elephants, that inhabited North and Central America during the late Miocene or late Pliocene up to their extinction at the end of the Pleistocene 10,000 to 11,000 years ago. Mastodons lived in herds and were predominantly forest dwelling animals that fed on a mixed diet obtained by browsing and grazing with a seasonal preference for browsing, similar to living elephants.
M. americanum, the American mastodon, is the youngest and best-known species of the genus. They disappeared from North America as part of a mass extinction of most of the Pleistocene megafauna, widely presumed to have been related to overexploitation by Clovis hunters, and possibly also to climate change.
The first remnant of Mammut, a tooth some 2.2 kg (5 lb) in weight, was discovered in the village of Claverack, New York, in 1705. The mystery animal became known as the "incognitum". The first bones to be collected and studied scientifically were found in 1739 at Big Bone Lick State Park, Kentucky, by French soldiers, who carried them to the Mississippi River, from where they were transported to the National Museum of Natural History in Paris. Some time later, similar teeth were found in South Carolina, which, according to the slaves, looked remarkably similar to those of African elephants. This was soon followed by discoveries of complete bones and tusks in Ohio; people started referring to the "incognitum" as a mammoth, like the ones that were being dug out in Siberia. Anatomists noted that the teeth of mammoth and elephants were different from those of the "incognitum", which possessed rows of large conical cusps, indicating that they were dealing with a distinct species. In 1806 the French anatomist Georges Cuvier named the 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Mastodon as a genus name is obsolete; the valid name is Mammut, a name that preceded Cuvier's description, making Mastodon a junior synonym.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.
M. americanum, the American mastodon, the best known and the last species of Mammut. Its earliest occurrences date from the early-middle Pliocene (early Blancan stage). It had a continent-wide distribution, especially during the Pleistocene epoch, known from fossil sites ranging from present-day Alaska and New England in the north, to Florida, southern California, and as far south as Honduras. The American mastodon resembled a woolly mammoth in appearance, with a thick coat of shaggy hair. It had tusks that sometimes exceeded 5 meters (16 ft) in length; they curved upwards, but less dramatically than those of the woolly mammoth. Its main habitat was cold spruce woodlands, and it is believed to have browsed in herds. It became extinct at the end of the Pleistocene approximately 11,000 years ago.
M. matthewi—found in the Snake Creek Formation of Nebraska, dating from the late Hemphillian. Some authors consider it practically indistinguishable from M. americanum. There is one report of it in China.
M. raki—Its remains were found in the Palomas Formation, near Truth or Consequences, New Mexico, dating from the early-middle Pliocene, between 4.5 and 3.6 Ma. It coexisted with Equus simplicidens and Gigantocamelus and differs from M. americanum in having a relatively longer and narrower third molar, similar to the description of the defunct genus Pliomastodon, which supports its arrangement as an early species of Mammut. However, like M. matthewi, some authors do not consider it sufficiently distinct from M. americaum to warrant its own species.
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 four 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. Compared to mammoths, mastodons had shorter legs, a longer body and were more heavily muscled, a build similar to that of the current Asian elephants. The average body size of the species M. americanum was around 2.3 m (7 ft 7 in) in height at the shoulders, corresponding to a large female or a small male, but large males could grow up to 2.8 m (9 ft 2 in) in height. However, the 35-year-old specimen AMNH 9950 grew 2.89 metres (9.5 ft) tall and weighed 7.8 tonnes (7.7 long tons; 8.6 short tons), and another male grew 3.25 metres (10.7 ft) tall and weighed 11 tonnes (11 long tons; 12 short tons).
Like modern elephants, the females were smaller than the males. They had a low and long skull with long curved tusks, with those of the males being more massive and more strongly curved. Mastodons had cusp-shaped teeth, very different from mammoth and elephant teeth (which have a series of enamel plates), well-suited for chewing leaves and branches of trees and shrubs.
Based on the characteristics of mastodon bone sites, it can be inferred that, as in modern proboscideans, the mastodon social group consisted of adult females and young, living in bonded groups called mixed herds. The males abandoned the mixed herds once reaching sexual maturity and lived either alone or in male bond groupings. As in modern elephants, there probably was no seasonal synchrony of mating activity, with both males and females seeking out each other for mating when sexually active.
Mastodons have been characterized as predominantly browsing animals.[note 1] Most accounts of gut contents have identified coniferous twigs as the dominant element in their diet. Other accounts (Burning tree mastodon) have reported no coniferous content and suggest selective feeding on low, herbaceous vegetation, implying a mixed browsing and grazing diet, with evidence provided by studies of isotopic bone chemistry indicating a seasonal preference for browsing.
The range of most species of Mammut is unknown as their occurrences are restricted to few localities, the exception being the American mastodon (M. americanum), which is one of the most widely distributed Pleistocene proboscideans in North America. M. americanum fossil sites range in time from the faunal stages of Blancan to Rancholabrean and in locations from as far north as Alaska, as far east as Florida, and as far south as the state of Puebla in central Mexico, with an isolated record from Honduras, probably reflecting the results of the maximum expansion achieved by the American mastodon during the Late Pleistocene. A few isolated reports tell of mastodons being found along the east coast up to the New England region, with high concentrations in the Mid-Atlantic region. There is strong evidence indicating that the members of Mammut were forest dwelling proboscideans, predominating in woodlands and forests, and browsed on trees and shrubs. They apparently did not disperse southward to South America, it being speculated that this was because of a dietary specialization on a particular type of vegetation.
Fossil evidence indicates that mastodons probably disappeared from North America about 10,500 years ago as part of a mass extinction of most of the Pleistocene megafauna that is widely presumed to have been a result of human hunting pressure. The latest Paleo-Indians entered the Americas and expanded to relatively large numbers 13,000 years ago, and their hunting may have caused a gradual attrition of the mastodon population. Analysis of tusks of mastodons from the American Great Lakes region over a span of several thousand years prior to their extinction in the area shows a trend of declining age at maturation; this is contrary to what one would expect if they were experiencing stresses from an unfavorable environment, but is consistent with a reduction in intraspecific competition that would result from a population being reduced by human hunting.
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