Proboscidea
Midwestern Elephant Relatives
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 the gomphothere 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.
Anatomy
(BELOW) Features of the skulls of proboscideans, in this case the gomphothere Cuvieronius. The large tusks found in many types of proboscideans are composed of a pair of enlarged incisors. Some proboscideans had lower jaw tusks as well.
Skull and Dentition
One of the defining features of proboscideans both living and extinct is their large, highly modified skulls. In many proboscideans, the skull is saturated with air-filled cavities that make the bones more lightweight without losing the strength needed to hold the mass of the trunk and tusks. Living elephants have a tall, sometimes domed skull with enlarged nasal openings situated high on the face. This position is linked to the shape of the base of the trunk. Extinct proboscidean groups each had their own special suites of skull features which ranged from the longer, lower-profile skulls of amebelodontids which often held long tusks on their lower jaws, as well as the more familiar skull shapes seen in animals like mammoths. The teeth of proboscideans changed quite a bit over the course of their evolutionary history as well. Early members of the group had a larger number of teeth than their modern relatives and had relatively simple molars with low crowns. Over time molar structure became increasingly specialized. Mastodons had molars with tall cusps suited for browsing on woody vegetation, while mammoths and modern elephants evolved large flattened grinding teeth characterized by multiple enamel ridges which are perfect for chewing up grasses and other tough silicate-rich plant matter. In many species the upper incisors eventually turned into tusks which, depending on the genus, could be straight, curved or even spiral-shaped.
(BELOW) Lower jaws of two types of extinct proboscideans on display at the KU Natural History Museum. Mammoth jaw on the left side of the image, mastodon lower jaw on the right. Note the differences in the shapes of the molars.
Postcranial Skeletal Anatomy
Most proboscideans were/are rather large animals. As a result of their size, most of their skeletal anatomy is adapted for holding up extreme amounts of weight. These animals have massive, pillar-like limbs which are thick and heavily reinforced. Their nearly vertical orientation beneath the body helps to reduce mechanical stress as these animals move. Compared with many other mammals, the lower limb joints of proboscideans are quite inflexible and are supported by a cushioned pad beneath each foot. Their vertebral columns and rib cages are similarly sturdy and often very wide.
(BELOW) A labeled diagram of the skeletal anatomy of a Columbian mammoth, based on the skeletal mount from the University of Nebraska State Museum of Natural History.
External Anatomy
Modern elephants have relatively little body hair and, in many species, they additionally have large ears that they can use to cool down by flushing them with blood. In contrast, woolly mammoths and possibly some mastodons were covered by a thick coat of fur and an insulating underlayer, adaptations for survival in cold environments. Proboscideans living in colder climates also likely had smaller ears in order to keep their body heat from escaping. Mammoths and other Pleistocene proboscideans living in warmer climates may have had mostly hairless skin like that seen in living elephants.
(BELOW) Features of the external anatomy of the proboscidean Stegomastodon from the early Pleistocene epoch
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 had 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 mounted mammoth skeletons in the world.
(ABOVE) A skeleton of a Columbian mammoth, nicknamed "Archie" on display the University of Nebraska State Museum of Natural History, Morrill Hall. Woolly mammoth skeleton in the background on the right.
(ABOVE) An adult mammoth tooth (left) compared with a tooth from a juvenile (right). Mammoths and other proboscideans lost their teeth as they got older and new sets moved in to take their place. Teeth are on display at the KU Natural History Museum in Lawrence, KS.
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.
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!
(ABOVE) A mastodon tooth on display at the KU Natural History Museum. The tall cusps on these teeth were well adapted for processing woody browse. Worn teeth of this size are found in older individuals.
(ABOVE) A mastodon skeleton on display the University of Nebraska State Museum of Natural History, Morrill Hall. Unlike mammoths, these mastodons did not have a prominent dome on their foreheads.
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 had 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.
(ABOVE) A skeleton of Stegomastodon on display the University of Nebraska State Museum of Natural History, Morrill Hall. Note the length of the tusks in this animal and the width of the bones of the ribcage and pelvis
Media Gallery
Suggested References: Proboscidea
Bader, Camille; Delapré, Arnaud; Göhlich, Ursula B.; Houssaye, Alexandra (2024). "Diversity of limb long bone morphology among proboscideans: how to be the biggest one in the family". Papers in Palaeontology. 10 (6) e1597.
Dooley Jr., Alton C.; Scott, Eric; Green, Jeremy; Springer, Kathleen B.; Dooley, Brett S.; Smith, Gregory James (2019). "Mammut pacificus sp. nov., a newly recognized species of mastodon from the Pleistocene of western North America". PeerJ. 7 e6614
Louguet-Lefebvre, Sophie (2013). "The Columbian mammoths from the Upper Pleistocene of Hot Springs (South Dakota, United States)". Paléo. 24 (24): 149–171.
Pérez-crespo, V. A.; Prado, J. L.; Alberdi, M. T.; Arroyo-cabrales, J.; Johnson, E. (2016). "Diet and habitat for six American Pleistocene proboscidean species using carbon and oxygen stable isotopes". Ameghiniana. 53 (1): 39–51.
Lucas, Spencer G.; Aguilar, Ricardo H.; Speilmann, Justin A. (2011). "Stegomastodon (Mammalia, Proboscidea) from the Pliocene of Jalisco, Mexico and the species-level taxonomy of Stegomastodon". New Mexico Museum of Natural History and Science Bulletin. 53: 517–553.
Mothé, Dimila; Avilla, Leonardo S.; Cozzuol, Mário; Winck, Gisele R. (2012). "Taxonomic revision of the Quaternary gomphotheres (Mammalia: Proboscidea: Gomphotheriidae) from the South American lowlands". Quaternary International. 276–277: 2–7.
Mead, Jim I.; Arroyo-Cabrales, Joaquin; Swift, Sandra L. (2019). "Late Pleistocene Mammuthus and Cuvieronius (proboscidea) from Térapa, Sonora, Mexico". Quaternary Science Reviews. 223 105949.
Mothé, Dimila; Avilla, Leonardo S.; Cozzuol, Mario A. (2012). "The South American Gomphotheres (Mammalia, Proboscidea, Gomphotheriidae): Taxonomy, Phylogeny, and Biogeography". Journal of Mammalian Evolution. 20: 23–32.
Nabavizadeh, Ali (2024). "Of tusks and trunks: A review of craniofacial evolutionary anatomy in elephants and extinct Proboscidea". The Anatomical Record. 308 (11) ar.25578.
Sanders, William J. (2023). "Chapter 3:Late Paleogene: First Major Diversification and Adaptive Radiation of Proboscideans". Evolution and Fossil Record of African Proboscidea. CRC Press. pp. 45–99.
Sanders, William J. (2017). "Horizontal tooth displacement and premolar occurrence in elephants and other elephantiform proboscideans". Historical Biology. 30 (1–2): 137–156.
Smith, Gregory James; DeSantis, Larisa R. G. (2020). "Extinction of North American Cuvieronius (Mammalia: Proboscidea: Gomphotheriidae) driven by dietary resource competition with sympatric mammoths and mastodons". Paleobiology. 46 (1): 41–57.