How mammoths competed with other animals and lost

The Gray Fossil Site, a sinkhole in northeastern Tennessee, is full of prehistoric treasures. Between 7 million and 4.5 million years ago, rhinoceroses, saber-toothed cats and other creatures, even red pandas, perished here by the edge of a pond. But that bounty of fossils pales next to the site’s biggest find: a mastodon’s skeleton, nearly 5 million years old, preserved in exquisite detail all the way down to its ankle bones. “It is just fantastic,” says Chris Widga, a paleontologist at East Tennessee State University in nearby Johnson City.

The ancient elephant relative became known as Ernie because it was enormous, calculated soon after its 2015 discovery to have weighed 16 tons in life. The name came from musician Tennessee Ernie Ford, known for the coal-mining song “Sixteen Tons.” Since then the researchers have revised the mastodon’s weight down to 10.5 tons, says Widga, but the name stuck.

Ernie is still the biggest mastodon ever found in North America. He would have dwarfed today’s large African elephants, which average up to six tons. Excavators are working to dig up the rest of Ernie’s bones before this winter, with an eye to reassemble the ancient beast, the researchers reported in October in Albuquerque at a meeting of the Society of Vertebrate Paleontology.

Ernie is a jaw-dropping example of the ancient elephants that once roamed Earth. Scientists have found the remains of mastodons and their relatives, the mammoths, throughout the Northern Hemisphere — from huge tusks buried in the Alaskan permafrost to mummified baby mammoths in Siberia (SN Online: 7/14/14).

Now, researchers are knitting together these scattered discoveries into a more coherent picture of the lives and deaths of mammoths and mastodons. Scientists are exploring what plants these megaherbivores ate as they rambled across the landscape, and how they competed with other animals — including humans — as climate changed and the last ice age ended some 11,700 years ago.

Clues to these mysteries lie in ancient teeth and bones. Tiny scratches on the teeth of mastodons from North America suggest that they ate a surprisingly varied diet of grasses, twigs and other plants, depending on their environment. A recent analysis of the chemistry of European mammoth bones reveals that those animals probably struggled with dwindling food sources as the climate warmed, which probably hastened the animals’ demise.

Excavating some of the last known sites where mammoths and humans coexisted points to how early Americans gathered around a kill, making the most of the giant carcass to feed themselves.

Scientists hope to better understand the extinct elephants’ role in ancient ecosystems. “How did these big herbivores respond to climatic shifts, both before and after humans arrived?” asks Hendrik Poinar, a geneticist and anthropologist at McMaster University in Hamilton, Canada. “How resilient were these populations — or not?”

The answers may even help biologists eke out lessons about how modern elephants might cope as habitats shrink and hunting pressures rise. 

Regional diets

Roughly a dozen species of mammoths and mastodons ranged across the globe at different times in the last 25 million years. The last of them died out for the most part at the end of the Pleistocene Epoch, which marked the end of the last ice age. The most famous is the woolly mammoth (Mammuthus primigenius), which appeared on the scene relatively late, around 350,000 years ago, and survived long enough to coexist with early humans in North America, Europe and Asia. Its shaggy coat and upturned tusks have made it an ice age icon, famous for roaming northern grasslands alongside saber-toothed cats, cave bears and other extinct beasts.

North America also had the Columbian mammoth (Mammuthus columbi), which arose about 1 million years ago and was bigger and less hairy than the woolly mammoth. It wandered as far south as Central America and left its heavy footprints in places like White Sands National Monument in New Mexico. Park rangers there have studied vast “trample grounds,” where herds of Columbian mammoths once thundered across the landscape.

A third extinct relative of elephants is the mastodon, including the American version (Mammut americanum). Mastodons were typically smaller and longer-bodied than mammoths, and quite a bit heftier. “We often think of mammoths as the supermodels of the Pleistocene, long, slender, very tall animals for their weight,” Widga says. In contrast, “mastodons are stocky.”

To tell a mammoth from a mastodon, start at the teeth. Mastodon teeth have cone-shaped tips, unlike the broad, flat teeth of mammoths. That suggests that mastodons gnawed on more branches, twigs and leafy things as opposed to the grasses that mammoths ground between their teeth.

With new detailed dental studies, researchers are getting a closer look at the animals’ diets. Paleoecologists Gregory Smith and Larisa DeSantis of Vanderbilt University in Nashville recently teamed up with Jeremy Green, a paleontologist at Kent State University in Ohio. They looked at patterns of wear, like the small pits left by nuts or acorns and the elongated scratches left by blades of grass. The team’s study of 65 mastodons from across North America, dating from 51,000 to 11,000 years ago, showed one group of mastodons ate very different plants than another, depending on where the animals lived. In Florida, the teeth indicated that the mastodons had been chewing on relatively soft material, perhaps the delicate tips of cypress trees. In Missouri, mastodons ate harder materials, such as seeds and bark. In New York, they chewed on conifer needles and twigs.

This rare effort to look at mastodon diets across a big geographic area, reported last year in Palaeogeography, Palaeoclimatology, Palaeoecology, shows that mastodons were adaptable. They chomped whatever trees and shrubs were common in their habitat. “It really hadn’t been proven until we started looking at it,” Smith says.

Those mastodons, at least, were flexible enough to change food sources as they migrated across the landscape. Another big ice age herbivore was not as adaptable, Smith reported in October at the Albuquerque meeting.

Living across both North and South America were the gomphotheres (including the genus Cuvieronius). These elephant relatives were smaller than mammoths and mastodons and had a body shape and size more like a modern elephant. Gomphotheres were hunted by early Americans (SN: 8/9/14, p. 7), but the creatures had also begun to dwindle well before people arrived on the scene.

The decline of the gomphotheres is surprising because they could eat just about any plant, from woody material to grasses. In theory, the animals should have been able to adapt to any food source. And yet they were apparently unable to cope as mammoths and mastodons moved into their chomping grounds, and as climate change squeezed the available resources.

To find out why, Smith compared patterns of tooth wear and other evidence from mammoths, mastodons and gomphotheres that once lived along the Gulf coastal plains of Texas and Florida. Starting around 1.8 million years ago, gomphotheres switched from grazing to eating a wider range of foods, Smith found. But the mammoths were already well specialized for eating grasses, and mastodons for eating the woodier plants. Gomphotheres couldn’t compete with the other elephants, Smith reported.

Ultimately, gomphotheres began to disappear from the scene. Only a few lingered until their final extinction, by at least 11,000 years ago.

Competing interests

On the other side of the Atlantic Ocean, a similar battle for resources in the face of climate change unfolded. This time, though, mammoths were competing with horses.

Chemical clues in an animal’s teeth and bones show variations of elements, or isotopes, specific to the types of plants or meat eaten.

Certain plants contain extra neutrons in the atomic nuclei of some of their elements. That distinction is reflected in the isotopic makeup of the skeletons of animals that ate those plants. Meat eaters retain a record of the plant eaters that they ate.

Compared with other herbivores, mammoths have unusual isotopes. Their bones are typically higher in the isotope nitrogen-15, even when compared with horses and other grazing animals in the same region. It may be that mammoths preferred to eat mature and dry grasses, which are higher in nitrogen-15 than younger, greener grasses preferred by other grazers.

But there’s one place where mammoths did not show the high nitrogen-15 levels: a site called Mezhyrich in Ukraine, which is famous for its prehistoric huts made of mammoth bones. Mezhyrich bones contain far less nitrogen-15 than is typical for mammoths. “For me, it was something absolutely new and unusual,” says biogeochemist Dorothée Drucker of the University of Tübingen in Germany.

To see what was going on, she and colleagues recently studied mammoth bones from other sites near Mezhyrich. All date to around 18,000 to 17,000 years ago, a time when the landscape was gradually warming. These other bones, too, contained surprisingly low levels of nitrogen-15. In fact, they were as low as the nitrogen-15 levels found in horse bones from nearby and dating to the same time period, the researchers reported in a paper published online in June in Quaternary Research.

That suggests that mammoths weren’t grazing on their usual grasses rich in nitrogen-15. Instead, something had apparently forced them to shift to a new menu. Perhaps the changing climate altered the types of vegetation growing in the mammoth landscape, shifting from rich and diverse grasslands to a less productive shrubland. Having to compete with other grazers, such as horses, for this less-preferred diet some 17,000 to 13,800 years ago may have been one of the last straws.

Dinner camp

Of course, climate change wasn’t the only thing stressing mammoths and mastodons as the last ice age wound to a close.

People hunted mammoths across Europe and northern Asia for thousands of years, possibly contributing to the animals’ gradual decline (SN: 7/27/13, p. 10). In North America, the downfall was more abrupt. Mammoths and mastodons roamed without major predators for hundreds of thousands of years or more. Then humans crossed a land bridge from Siberia to Alaska probably some time after 16,000 years ago (SN Online: 8/8/18), bringing with them the knowledge of how to use spears to take down the huge hairy beasts.

Scientists have argued for decades about how much human hunting versus climate and other environmental changes contributed to the death of North America’s mammoths and mastodons. Todd Surovell, an archaeologist at the University of Wyoming in Laramie, says the evidence points mostly to people. “Humans arrived to a continent full of large naïve animals,” he says. The mammoths were “easy pickings,” he says, “practically like a herd of cattle.”

Surovell studies archaeological sites where humans butchered mammoths, mastodons or gomphotheres. He and colleagues have spent the last few years excavating a 12,900-year-old site known as La Prele, in eastern Wyoming. It is one of about 15 butchery sites known of in North America.

When first discovered in 1986, the site yielded part of a mammoth and a few stone tools. In 2014, Surovell and his team stumbled on archaeological gold. While widening a path 12 meters away from the 1986 find, a team member’s shovel struck a large stone artifact, a tool probably used for chopping. “All of a sudden the site expanded hugely,” Surovell says.

Since then, the researchers have unearthed a dramatic story of how early hunters gathered triumphantly around their kill. The mammoth bones mark where the animal lay; nearby is a string of fire pits, presumably where people camped as they butchered the meat. Near the campfires lie domestic artifacts such as bone needles and bone beads, which suggest that several families or a small village temporarily settled around the mammoth kill.

“We always expected to find campsites associated with animals, but this is only the second time we’ve found this kind of thing archaeologically” in North America, Surovell says. For a smaller animal, hunters might have cut up the carcass and carried the meat back to their camp. That wasn’t possible for a mammoth, which could have weighed up to 10 tons. Instead, the people “moved their camp to the mammoth,” he says. Surovell has presented findings from the La Prele site at various small archaeology meetings.

Based on the number of artifacts at La Prele, Surovell thinks the people may have stayed around the carcass for perhaps a week, feasting and drying meat to take with them. There’s no question that humans ate mammoth; Drucker, among others, has found high nitrogen-15 levels in the bones of early European humans, which suggest the people derived a large fraction of their protein from mammoth meat.

Ultimately, many experts say, mammoths and mastodons probably went extinct because of some combination of human hunting and climate change, with those factors varying around the globe. Different species winked out at different times in different locations; most vanished by around 11,000 years ago as the great northern ice sheets receded and temperatures rose. A few isolated herds hung on for another few thousand years.

One group of woolly mammoths made it until about 5,600 years ago on St. Paul Island, north of Alaska’s Aleutian Islands. The animals probably died out when the island’s lakes dried up (SN Online: 8/1/16). Another group survived all the way until 4,000 years ago on Wrangel Island off Siberia, where genetic studies suggest that the creatures eventually succumbed to too much inbreeding.

Once those last animals vanished, it was the end of the mammoth lineage. But understanding their fate may help researchers help modern elephants. Across Asia and Africa, elephants are facing some of the same stresses that mammoths and mastodons did long ago. Climate change is reshaping the landscape. Humans are hunting elephants and destroying their habitat.

The lessons of the past might help conservationists come up with new ways to help elephants survive, Smith says. “The fossil record can tell us what happened in the past in similar circumstances,” he says. “My hope is that a better understanding of ancient ecology can give us some insight into the future.”

Poinar agrees. He and grad student Emil Karpinski are working on the biggest analysis of mastodon DNA. They have more than 100 samples gathered from around the Northern Hemisphere. (Sadly, Tennessee Ernie is too old for good DNA preservation.) The researchers hope to show how mastodon populations grew and shrank over time, and how those changes were linked to shifting climate and to human hunting.

“It’s no shock to say that humans have played a drastic role in extinctions in the past and are doing so as we speak,” Poinar says. “But if we were to leave species on their own, how would climate change affect their ability to be resilient?”

The answers, when they come, may just show what today’s elephants need to survive.

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This article appears in the November 24, 2018 issue of Science News with the headline, “A Mammoth World: How ice age beasts competed with other animals and lost.”