Mammoths and Mastodons: All American Monsters

A mammoth discovery in 1705 sparked a fossil craze and gave the young United States a symbol of national might

Columbian mammoths were larger than mastodons. Both once roamed North America. (Velizar Simeonovski / The Field Museum, Chicago)
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Buffon’s theory of American degeneracy was still on Jefferson’s mind years later, when, as president, he sent Lewis and Clark to explore the American West—partly to see if they could turn up a living mammoth. He was so obsessed with this quest that he once laid out a collection of mastodon and other bones on the floor of the East Room in the White House, where John and Abigail Adams’ laundry had once hung.

Jefferson was right about the robustness of American wildlife. At Larry Agenbroad’s dig at the Mammoth Site in South Dakota, a volunteer from the Earthwatch Institute carefully scrapes dirt from around the rib of a giant short-faced bear, the largest bear species ever known. It weighed 1,200 pounds or more and could stand 15 feet high, half again the regulation height of a basketball rim. Bears, wolves and other carnivores apparently preyed on mammoths struggling at the edge of the thermal pool—and sometimes also died there. Agenbroad has not yet found any lion bones among all the mammoth remains at the site, but just as Jefferson suspected, an American lion—25 percent larger than its modern African counterpart—also once roamed the Great Plains.

Columbian mammoths, the North American species named for Christopher Columbus, stood up to 14 feet tall at the shoulder, towering two feet over African elephants. One woolly mammoth, at most ten feet tall, has also been found at the site, dating to an undetermined time when the climate got colder and Col­umbian mammoths moved south. There are no mastodons at the site, and in the spirit of geographic one-upmanship, Agenbroad dismisses those eight- to ten-foot-tall Easterners as deficient—though not quite degenerate—cousins.

Agenbroad first came to the Hot Springs site in July 1974 on a quick visit from a bison dig an hour or so south. George “Porky” Hanson, a bulldozer operator, had scraped up a mess of bones while getting the area ready for a housing development. Hanson’s son, who had taken a course from Agenbroad at Chadron State College in Nebraska, sent him a note: “We think we have mammoths in Hot Springs.”

They did, and digging commenced in earnest in 1975. The housing developer agreed to back off for three years and, after the scope of the discovery became apparent, sold the property at cost to a nonprofit foundation that Agenbroad helped establish. Work on the site since then has produced—along with 116 tusks and tons of bones—an explanation of what happened there 26,000 years ago.

Some of the Mammoth Site animals died at first snow, according to Agenbroad, and others during an early spring thaw. (Researchers determined the season of death with the help of trace isotopes in different tusks.) The ice age winter, Agenbroad says, left mammoths with two choices: “They could sweep off three feet of snow and get last year’s grass, which is about as exciting as a bowl of cereal with no sugar, berries or milk. Or they could go for the salad bar of plants still growing around the edge of the sinkhole—just like bison in Yellowstone National Park go for the green grass around thermal pools.”

But the sides of the sinkhole sloped at least 67 degrees, Agenbroad estimates, and the stone—Spearfish Valley red shale—gets as slick as grease when wet. Only males were dumb enough to risk it, he figures, because female mammoths stayed within the shelter of the herd their entire lives, like modern elephants. But adolescent males went into exile—and did the sort of imprudent things adolescent males still do today.

Early in the excavation, the concentrated pattern of bones made it practical to think about putting the whole site under a roof. “We made the decision to leave the bones where they were,” Agenbroad says. “They never look the same on a shelf.” The Mammoth Site foundation’s board of directors has always been notably local (Porky Hanson was a member), but Agenbroad persuaded them of the value of emphasizing science, not just tourism. The site now attracts 110,000 visitors a year.

Out on a part of the excavation she calls her “airstrip,” a volunteer named Ruth Clemmer uses a square trowel to make thin shavings of dirt buckle up and away. This is the end of her fifth two-week work session over the past three years, and she can add up what she’s found in that time: one toe bone the size of her fist, one coprolite (fossilized excrement, probably from a wolf) and many mammoth rib fragments. Ribs are cheap around here, since each animal had 40 of them. “If we had a barbecue joint, we’d be in business,” jokes another volunteer.

About Richard Conniff
Richard Conniff

Richard Conniff, a Smithsonian contributor since 1982, is the author of seven books about human and animal behavior.

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