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The American mastodon (Mammut americanum) is an extinct species of proboscidean. Although they likely resembled mammoths and elephants in external appearance, American mastodons belong to the taxonomic family Mammutidae and mammoths and elephants to Elephantidae. The earliest record of the American mastodon dates to about 3.75 million years ago, and comes from south-central Washington in the United States. In Canada, fossil evidence of American mastodons is restricted to the latter portions of the Pleistocene epoch (2.68 million–10,000 years ago). American mastodons lived across much of Canada. Paleontologists have found fossils in Yukon, the Northwest Territories, British Columbia, Alberta, Saskatchewan, Manitoba, Ontario, Quebec, Nova Scotia, and New Brunswick. Later records of mastodons in Canada overlap in time with archaeological records of Indigenous people. However, while there is evidence that people hunted American mastodons at the Manis Site in Washington, to-date no similar evidence has been found in Canada. American mastodons went extinct around 10,000 years ago.
Fossil Record in Canada
During the Ice Age, glaciers moved across much of Canada. This movement likely eroded away much of the fossil record of large, extinct Ice Age mammals, including mastodons. Although much of the record of the American mastodon consists of isolated skeletal elements, there are a few exceptional records. For example, paleontologists found an adult male skeleton (60 per cent complete) and a juvenile (10 per cent complete) in East Milford, Nova Scotia. In addition, a partially complete skeleton was found in Hillsborough, New Brunswick. In both instances, the finds included both dung and bones.
The geologic age of American mastodon fossils vary across Canada. Most records in Yukon and Alberta are older than can be accurately dated by radiocarbon (i.e., more than roughly 45,000 years before present). However, many of the records from Eastern Canada indicate the more recent presence of mastodons (e.g., about 12,000 years before present). Another contemporary species of mastodon, Mammutpacificus, occurs in the fossil record of the Western United States. However, the presence or absence of that species in Canada requires further research. Paleontologists found a rare, middle Miocene (16.3–13.6 million years ago) record of Zygolophodon proavus, a related taxon, in Saskatchewan.
Description
American mastodons resembled mammoths and elephants in external appearance. However, features of their skeleton point to a distinct evolutionary history. In particular, the teeth of American mastodons have large cusps on the chewing surface. This is in contrast to the flattened series of enamel plates that characterize the chewing surface of mammoth and elephant teeth. American mastodons stood between about 2.4 and 3.0 m at the shoulder, with some females as short as 2.3 m. Body weight ranged from 4 to 5 tons. American mastodons were heavily built, with short, thick limbs, giving them a stockier appearance than the distantly related mammoths. The head was low-domed and the back shape was straighter than that of mammoths. Mastodons may have had a dense coat of coarse, brownish hair.
American mastodons had three cheek teeth on each side of their lower and upper jaws. “Baby” cheek teeth were replaced by permanent teeth through the maturation of an individual. Their upper tusks projected horizontally from the skull, curving outward and then inward closer to the tips of the tusk. Some males also had tusks on their lower jaw.
Evolution
American mastodons evolved in North America. They were the last of an evolutionary lineage that originated in Africa approximately 22 million years ago. Ancestral populations that may have given rise to American mastodons first travelled to Canada during the middle Miocene (15.5 million years ago) via the Bering Strait, when low sea levels created a land bridge between Canada and portions of Eastern Russia. Different hypotheses regarding whether or not those ancestral populations arrived in North America all at once or over the course of multiple journeys shape the view of how American mastodons evolved.
Research on DNA preserved in fossils dating to the last Ice Age (i.e. 2.6 million to about 10,000 years old) revealed interesting patterns of movement of the species across North America. During the Ice Ages, American mastodons likely dispersed northward when warmer, interglacial cycles permitted the expansion of forests and wetlands into areas of Alberta and Yukon. As climate shifted to colder conditions, northern populations became locally extinct, only to be replaced by different, northward dispersing populations during the next interglacial cycle.
Distribution and Habitat
In Canada, paleontologists have recovered fossil remains of the American mastodon from every territory except Nunavut, and every province except Newfoundland and Labrador and Prince Edward Island. Remains of American mastodon are rare in the West, but more common in portions of Eastern Canada, particularly in Ontario near Lake Erie.
Cross-Canada differences in abundance of American mastodon fossils may reflect differences in the species’ habitat preferences and distribution patterns. Remains of American mastodon are commonly associated with woodland environments (e.g., spruce-dominated forests) that grew in Canada and the United States during the Pleistocene epoch. Fossils found in the West are likely related to expansions of those woodlands during interglacial cycles.
Diet
The American mastodon’s diet consisted of trees, shrubs, and herbs found in woodlands and similar habitats. Sedges and grasses found from the intestines of a mastodon from Ohio indicate some grazing, perhaps reflecting seasonal differences in diet. Direct evidence of the diet of American mastodons in Canada comes from dung recovered with skeletal remains in New Brunswick and Nova Scotia. Spruce needles, birch macrofossils and sedges were abundant in dung associated with a juvenile American mastodon from East Milford, Nova Scotia. Spruce, pine, and alder pollen were abundant in remains interpreted as dung from Hillsborough, New Brunswick.
Life History and Behaviour
American mastodons were likely long-lived with life spans exceeding 50 years. They probably had some form of social structure similar to living elephants, where adult females and juveniles formed groups or herds. An assemblage of bones from Boney Spring, Missouri, includes individuals of mixed-ages that likely died at the same time. American mastodons may also be responsible for the dispersal of some skeletal elements at Boney Spring. This reflects a behaviour observed when living elephants encounter the remains of deceased elephants.
Extinction
The extinction of American mastodons and other large-bodied, Ice Age animals remains an area of intense study. Proposed causes of extinction include climate and environmental change, human predation, disease, and meteorite impact. American mastodons became locally extinct in some regions of Canada (Yukon) earlier than elsewhere in North America. This was likely because of ecological shifts that pre-dated the end of the Pleistocene epoch. Regardless of the cause, all populations of American mastodons became extinct across their range near the end of the Pleistocene epoch (about 10,000 years ago).
