Proboscidea
Elephant relatives in the Midwest
During the Pleistocene Epoch, the Midwest was home to several large proboscideans, the group of mammals that includes modern elephants. These animals represented many different forms of elephant-like mammals, including mammoths, mastodons and gomphotheres. Mastodons preferred forested environments, where they browsed on leaves, twigs, and shrubs, while mammoths were more adapted to open grasslands and fed primarily on grasses. Gomphotheres formed a group with a convoluted taxonomic history, possibly even including the direct ancestors of mammoths and living elephantids, as well as a diverse array of strange four-tusked extinct proboscideans. In the Pleistocene epoch, the last members of this group were animals like the spiral-tusked Cuvieronius. Fossil discoveries across Midwestern states such as Kansas, Missouri, Iowa, Illinois, and Indiana show that these giant mammals were important members of Pleistocene ecosystems until their extinction near the end of the Ice Age.
Cuvieronius hyodon
Temporal Range: 10 million years ago to approximately 10,700 years ago
Geographic Range: Found across North and South America
Species: C. hyodon, C. tropicus, C. oligobunis, C. priestleyi
Diet: Herbivorous mixed feeder, grass, leaves
Cuvieronius was an elephant-like proboscidean belonging to the trilophodont gomphothere group. It was one of the last surviving gomphotheres and ranged from the southern regions of North America through Central America before eventually spreading into South America.
Unlike mammoths and mastodons, Cuvieronius possessed distinctive tusks that twisted in a gentle spiral. Its lower tusks were greatly reduced or absent in adults. Fossil evidence indicates that it would have lived in a variety of environments, including open grasslands, woodlands, and subtropical habitats. Its flexible diet allowed it to consume a wide range of vegetation rather than specializing on either grasses or browse.
A few sites seem to show the remains of Cuvieronius preserved alongside stone tools, suggesting that the first humans to arrive in the Americas hunted these gomphotheres.
Columbian mammoth
Mammuthus columbi
Temporal Range: 1.5 million years ago to approximately 12,000 years ago
Geographic Range: Genus across North America, Central America
Species: M. columbi
Diet: Herbivorous grazer, grasses
The Columbian mammoth was the largest land mammal found in the Midwest during the Pleistocene. Up until around 12,000 years ago mammoths would have been a common sight all throughout North America. Their range extended from North Dakota all the way down to central Mexico and their remains are found along both the Atlantic and Pacific coasts. Mammoths were at home in grassland habitats where they would have lived alongside giant bison, camels and wild horses. The average adult columbian mammoth would have stood around 12 feet tall at the shoulder, although some very large individuals may have reached heights of 14 feet making them much larger than any elephant species alive today. A particularly large example of a Columbian mammoth skeleton, nicknamed Archie, is on display at the Nebraska State Natural History Museum in Lincoln. This particular specimen is one of the largest mammoth skeletons in the world.
Woolly mammoth
Mammuthus primigenius
Temporal Range: 400,000 years ago to approximately 4,000 years ago
Geographic Range: northers latitudes of North America, Eurasia
Species: M. primigenius
Diet: Herbivorous grazer, grasses
Woolly mammoths were fairly rare in the Midwest. They were almost entirely absent in the southern parts of the Plains and even in parts of South Dakota they seem to have been outnumbered by their larger relatives, the Columbian mammoths. At the Mammoth Site in Hot Springs, South Dakota, a Pleistocene bone bed preserves the remains of dozens of Columbian mammoths but only three woolly mammoths.
Woolly mammoths are well known for their thick coats of fur which would have offered them a great deal of protection from the cold. Some mammoth mummies have even been found with some of their fur coats still intact! Mammoths had longer legs than most of today's elephants and had a distinctive dome on top of their foreheads. The last of the woolly mammoths disappeared from a small island in the Arctic called Wrangel Island around 4,000 years ago, although by then they had been extinct on the mainland for thousands of years.
Stegomastodon nebrascensis
Temporal Range: 4 million years ago to 1.2 million years ago
Geographic Range: Found throughout North America
Species: S. nebrascensis, S. mirificus, S. aftonae, S. primitivus
Diet: Herbivorous mixed diet, grasses, leaves
Stegomastodon was an extinct proboscidean belonging to a group called the trilophodont gomphotheres. These were extinct elephant relatives that had flourished in North America during the Neogene period but became increasingly rare during the Pleistocene. Stegomastodon lived in North America from the Pliocene into the Early Pleistocene. Unlike earlier gomphotheres, which often possessed elongated jaws with a second set of lower symphysial tusks, Stegomastodon had a short lower jaw and only a pair of upper tusks, giving it a more elephant-like appearance than some of its ancestors. Its tusks curved upward and could reach impressive lengths.
Fossils of Stegomastodon have been discovered across much of North America, indicating that it occupied a wide range of habitats. These animals were once thought to have lived in South America but those southern species have since been folded into the genus Notiomastodon.
American mastodon
Mammut americanum
Temporal Range: 8 million years ago to approximately 11,000 years ago
Geographic Range: Genus is found across North America
Species: M. americanum, M. pacificum, M. nevadanum
Diet: Herbivorous browser, leaves
American mastodons were some of the first large animals whose fossils were recorded as having been found in North America. Their bones were likely found across the continent for thousands of years but the first recorded find of one of their fossils is likely a piece of a tooth surface found sometime around 1705. Early in their history of study, in the 19th century, the large cusps on the teeth of these animals were interpreted as a sign that they were carnivorous, although this idea was soon dismissed. We now know that these large cusped teeth were likely an adaptation for feeding on woody plant material.
Mastodons were found all across North America, from Alaska to central Mexico. These animals could be differentiated from mammoths by their stockier builds, straighter tusks, unique tooth surface shapes, and the lack of a large bony dome over their foreheads. They preferred to live in forest habitats. Although these animals are typically reconstructed with a thick coat of fur, some researchers have suggested that they might not have been very hairy after all, with their stockier build keeping them warm even in colder areas. This is still an unresolved question and future finds may give us more information about the life appearance of these ancient animals.
The American mastodon also has an important cultural presence in the US and has been designated the official fossil of the states of Michigan and Indiana!
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