Fossil of the month: Mastodon teeth and jaw fragment
This specimen is a fossil mastodon jaw (mandible) fragment with in-place molar (cheek) teeth. Mastodons (Mammut sp.) were a type of ice age elephant that once lived across much of North America during the Pleistocene Epoch. This specimen was found in northern Kentucky. It is on loan from the Department of Earth and Environmental Sciences Paleontological Collection at the University of Kentucky, for a display on the Ice Age at the Kentucky Geological Survey.
Description. Mastodons (Mammut) are a type of ancient elephant ancestor. They were similar in appearance to modern elephants. Like modern elephants, they had trunks. They also had tusks, although mastodons had shorter tusks than modern elephants or mammoths. Their front and back legs were similar in height (e.g., Haynes, 1993). A full-grown adult male mastodon, would have averaged 9.5 ft (2.9 m) at the shoulder, while male African elephants, average 10.5 ft (3.2 m) at the shoulder. Mastodons, however, were stockier (more robust) and heavier, than modern elephants (Larramendi, 2015).
Mastodons vs. Mammoths. Mastodons (Mammut) and mammoths (Mammuthus) are two types of ice age elephants that lived in what is now Kentucky. Genetic studies from fossils show mammoths, mastodons, and modern elephants are different branches of the elephant lineage. Mastodons are more distantly related to modern elephants than are mammoths (Rohalnd Palkopoulou and others, 2018). In the late 1700s and early 1800s, Georges Cuvier, a French scientist, was one of the first to do detailed studies of what would become known as mastodon and mammoth teeth. He named one type of teeth with high conical crowns, “Mastodonts,” for the Latin word for breast (cones)=mastos and the Greek word for teeth=odon (Cuvier, 1796, 1806). Cuvier, however, did not know that similar teeth had been given the name “Mammut” previously, so by the rules of paleontology, the official genus name of mastodons is the first name proposed, Mammut. Unfortunately, “Mammut” sounds a lot like “mammoth” (scientific name Mammuthus), which is a different genus of ice age elephant. The similar sounding names for two extinct elephants that lived at the same time, has led to much confusion through the years. To avoid confusion, Cuvier’s name (mastodon) remains as an informal, commonly used name (Haynes, 1993; Heeden, 2008).
In general, adult mammoths were taller and longer than adult mastodons. The tusks of adult mammoths were longer and more curved than the tusks of adult mastodons. There is considerable overlap, however, between the sizes of their bodies and tusks. Variation in sizes occurs because of differences between males and females and between juveniles and adults. A real distinction between mammoths and mastodons, regardless of age or sex, is the differences in their molar or cheek teeth (like our fossil of the month). Mammoth molars had broad, thin crowns, with small transverse ridges, somewhat like a giant file. In contrast, the crowns on mastodon molars consisted of pairs of connected cones with cusps (Cuvier, 1796, 1806; Skeels, 1962; Maglio, 1963; Haynes, 1993).
Range. Mastodons appear to have evolved from earlier animals with trunks called Gompotheres (Shoshani, 1998). The oldest mastodons are from the late Oligocene Epoch, Paleogene Period, 24 million to 28 million years ago (Rohland and others, 2007). The species, Mammut americanus, evolved later, and did not become widespread in North America until the Pleistocene Epoch, Quaternary Period. Mastodon fossils in Kentucky and Ohio are from the latest Pleistocene to early Holocene, mostly 25,000 to 11,000 years old (e.g., Tankersley and others, 2015). Mastodons went extinct in the early Holocene, between 11,000 and 10,000 years ago (e.g., Haynes, 1993).
Many fossil Mastodon bones have been found in Kentucky, mostly along the Ohio River, or in tributaries to the Ohio River. The most famous sites for mastodon fossils in Kentucky are Blue Licks and Big Bone Lick (Cooper, 1931; Jillson, 1936; Schultz and others, 1963). Big Bone Lick has been called the birthplace of North American paleontology because it was the site of the first purposeful excavation for finding and preserving fossil remains (including mastodons) in North America. Both Benjamin Franklin and Thomas Jefferson studied fossil mastodon bones from Big Bone Lick. Mastodon bones from Big Bone Lick are on public display at the state park, the Cincinnati Natural History Museum, and the Kentucky Geological Survey and Department of Earth and Environmental Sciences at the University of Kentucky.
Learn more about:
- Big Bone Lick
- Benjamin Franklin and mastodon teeth
- Thomas Jefferson, and big mammoth and mastodon bones
- Georges Cuvier, mastodons from Kentucky, and the idea of extinction
What do fossil teeth tell us about the way mastodons lived? You have probably heard the saying, “you are what you eat.” This is true for animals living today as well as for ancient animals. Animal teeth are tools which allow food to be processed in the mouth. Fossil teeth, like this month’s fossil, provide information about the animal they came from by (1) their shape, (2) the amount of wear and abrasion, and (3) their isotopic composition.
The shape of teeth enable different types of functions, such as slicing, stabbing, tearing, and grinding. By comparing the shape of fossil teeth to the teeth of animals that live today scientists can interpret if an ancient animal was a meat eater (carnivore), plant eater (herbivore), or at both meat and plants (omnivore).
Mastodons have teeth composed of pairs of conical structures, which is very different than modern elephants, or their ice age cousins, the mammoths. The shape of their teeth intrigued some of the early scientists who studied them. At first, many scientists thought the high cones meant that mastodons were carnivores. Cuvier (1796, 1806) used comparative anatomy with living organisms to argue that mastodons were plant eaters. Their high conical teeth would have been good at crushing twigs and other hard plant tissues. Thereafter, it was accepted that mastodons were herbivore browsers, with a diet of twigs, bark, and leaves from small trees and shrubs (Skeels, 1962; Maglio, 1963; Haynes, 1993; Heeden, 2008).
Modern studies of microwear texture on fossil mastodon teeth confirm a dominantly woody diet (bark, twigs), consistent with browsing, but with considerable variation depending on available plants in different areas (Rivals and others, 2012; Green and others, 2017).
Likewise, isotopic studies of fossil mastodon teeth also confirm a diet of woody, forest vegetation. Different types of plants are composed of different chains of carbon molecules. If a plant-eating animal has a diet dominated by a certain kind of plant, that plant’s composition can leave an imprint in the tooth, which can be detected through isotopic analyses (Smith and DeSantis, 2018).
In addition to these somewhat indirect methods for interpreting diet from fossil teeth, mastodons are a type of fossil for which rare, partial soft-part remains have been found in peat and lake- bottom sediments. From these, scientists have actual stomach and intestinal contents to interpret diet, which show a diet consisting of conifer twigs but in some areas including also deciduous trees, shrubs, and herbaceous plants (Webb et al., 1992; Laube and others, 1994; Teale and Miller, 2012).
More paleoecology. Mastodon remains are mostly found in stream and lake sediments. Mastodons appear to have lived in forested areas, and near streams and wetlands surrounded by forested areas (Skeels, 1962; Maglio, 1963; Haynes, 1993). At Big Bone Lick and Blue Licks, Kentucky, abundant mastodon fossils have been found, which indicates they often visited the salt licks. They shared these lakeside and streamside environments with other Pleistocene animals including mammoths, bison, woodland musk ox, stag moose, complex-toothed horse, giant sloths, and deer (Schultz and others, 1963; Tankersley and others, 2015).
Mastodon extinction. Mastodons went extinct 11,000 to 10,000 years ago. Mastodon, mammoth, and many other Ice Age large animals are considered to have gone extinct because of (1) hunting from paleo humans, called the “Pleistocene overkill hypothesis” (Martin, 1984; Fisher, 1987; Meltzer, 2015); (2) climate and subsequent vegetation changes following the last glacial advance (Guthrie, 1984; Graham and others, 1996; Yansa and Adams, 2012; Cooper and others, 2015); or combinations of the two. The loss of so many species of large mammals, is considered by many scientists to be a sixth mass extinction, sometimes called the Holocene extinction, or Anthropocene extinction (Leakey and Lewin, 1995; Ceballos and Ehrlich, 2018; Turvey and Crees, 2019).
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- Smith, G.J., and DeSantis, L.R., 2018, Dietary ecology of Pleistocene mammoths and mastodons as inferred from dental microwear textures: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 492, v. 1, p.10-25.
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Text and illustrations by Stephen Greb (KGS).