Emissary from an Ice-Age Boneyard

By Michelle Klampe, News and Research Communications

An ancient stream channel snakes 10 feet below the north end zone of Oregon State University’s Reser Stadium and under an adjoining parking lot. The sides slope gently upward in what may have been a bog or marsh. For about 12,000 years, the skeleton of a Columbian mammoth rested here, undisturbed.

In 2016, the animal’s quiet repose came to an end when a construction worker digging a foundation struck bone and set off a world-wide media frenzy. The novelty of finding a 5-foot long mammoth femur in the end zone of a college football stadium drew the notice of news outlets everywhere, from ESPN and USA Today to Yahoo Japan.

Additional excavation of a plot the size of a small pickup truck and about 10-feet deep revealed more of the mammoth’s skeleton, including part of the mandible, a molar and molar tooth plate, parts of the scapula, the pelvis, a knee cap and other bones.

The revelation sparked a scientific inquiry by faculty, graduate students and undergraduates from across the university. Together, they have been working for more than a year to understand the significance of the discovery. They have learned that the animal may have been among the last of its species at a pivotal transition in the ice-age landscape that would become western Oregon.

“It’s exciting to discover that you’ve got remains of extinct animals buried right here on campus,” says Loren Davis, an associate professor of anthropology in OSU’s College of Liberal Arts. “We’re working on a project that has a lot of local interest. We don’t have all the answers, and we’re figuring these things out together.”

Davis and Rebecca Terry, an assistant professor in the College of Science, are leading the effort to learn more about the Reser mammoth and the world it roamed.

An archaeologist whose primary research interest is the early history of hunter-gatherers in western North America, Davis typically studies sites where evidence of humans has been found. His expertise in stratigraphy — the study of soil layers — helps him to interpret artifacts such as stone tools, spear points and animal remains.

Terry is a paleontologist who works primarily with much smaller ancient animals, such as rats and mice. She uses the bones and teeth from owl pellet deposits (undigested, regurgitated food) to study how prehistoric climate change and human land use have affected animal communities over time.

Last of Its Line

The Columbian mammoth species was the last in a line that inhabited North America until its extinction around the end of the Pleistocene epoch, about 11,700 years ago. Considerably larger than a modern elephant, the animals weighed about 22,000 pounds and reached as high as 13 feet at the shoulder. Scientists think the species arrived in North America more than 1 million years ago and roamed throughout the northern United States and as far south as Costa Rica. The cause of extinction remains unclear, but climate change and exposure to humans are among the suspected contributors.

The discovery of the Reser skeleton challenges existing views about the timing for the Columbian mammoth’s extinction, which was thought to have occurred about 13,000 years ago. “The whole idea that this mammoth persisted that long makes us need to step back from the argument that these large animals went extinct abruptly at an earlier time,” Davis says. “It’s a compelling and interesting problem to think about.”

The ancient stream channel running under Reser Stadium was likely formed after the Missoula Floods, the cataclysmic ice-age torrents that rushed periodically across eastern Washington, down the Columbia River Gorge and into what we now know as the Willamette Valley. The geological conditions in the channel were ideal for preservation.

The stratigraphy indicates the bones were buried as the stream channel filled with clay. The water table also rose, creating a persistently wet condition that helped keep the bones from drying out and crumbling. Decay slowed as oxygen levels dropped.

Davis and his graduate student, J.D. Lancaster, oversaw the initial excavation, when the large bones were removed and huge piles of soil were pulled from the site. Dozens of OSU faculty and students spent a rainy winter day going through the mounds, searching for additional bones and fragments.

More than 50 bones and pieces have now been unearthed and nearly all of them appear to be from a single Columbian mammoth. Also found were a couple of toes from an ancient bison, a larger version of today’s modern bison that also roamed the region during the Pleistocene. The researchers found no signs of humans and have not seen any signs of human interaction with the mammoth.

“The evidence suggests that animals may have come to the stream and died there,” Davis says.

Preserving Bones for Science

Terry and her graduate student, Brian Tanis, led efforts to inventory, identify and preserve the specimens. Undergraduate students in Terry’s spring 2016 paleobiology class carefully prepared the bones for drying and long-term preservation. Most of the large and identifiable pieces are in an OSU storage facility for now.

“We have about 55 bones being supported in plaster or foam cradles. They need to dry out slowly over a period of years,” Terry says. “We have two bones that we still can’t identify. They might be heel bones or possibly broken parts of the pubis bone.”

After two failed attempts to determine the age of the bones with radiocarbon analysis, a Bothell, Washingon-based laboratory was able to successfully date the remains by using enamel from the tooth plate. Results indicate that the animal lived about 12,000 years ago, the youngest mammoth skeleton discovered in the Willamette Valley and maybe among the last to survive on the mainland of North America.

“That means that humans were co-existing with mammoths,” Terry said. “They were in the same places for about 2,500 years.”

Soil and Culture

Both Terry and Davis have conducted research at Paisley Caves, in south-central Oregon’s Summer Lake basin, where evidence of humans dates back to about 14,400 years and is the oldest known location of human remains — a coprolite, or fossilized feces — in North America. The caves are about 200 miles east of Corvallis, a distance short enough that Davis believes the humans there were likely to encounter mammoths roaming the region at that time.

“From a hunter-gatherer perspective, it makes sense that humans and mammoths would have encountered one another,” he says. “We don’t have a lot of information about the early Willamette Valley — the megafloods and other floods tended to bury things — so there may be other sites we haven’t yet found that show people interacting with mammoths.”

The climate in the Willamette Valley at that time would have been a bit dryer and a few degrees colder than it is today, but the terrain and vegetation would likely have been similar, giving the people and the mammoths plenty of vegetation on which to dine, he adds.

Davis and Lancaster extracted sediment core samples — two-inch cylinders of compacted soil and sediment in five-foot lengths stacked to a depth of at least 10 feet — from the area where the bones were discovered. Davis plans to send some organic material from the sediment cores for radiocarbon dating in an effort to further confirm the age of the mammoth.

The sediment cores also will help researchers understand the environment at the point when the mammoth roamed. The stratigraphy of the cores, which are still being analyzed, can provide further insight into the history and conditions of the area.

“The cores reveal the geologic history that’s buried at Reser Stadium. We can use that information to make interpretations,” says Davis, “about how local environmental conditions changed through time.”

Terry and her spring 2017 paleobiology students will begin going through more than 100 five-gallon buckets of dirt pulled from the construction site, looking for additional bone fragments or remnants of much smaller creatures such as rodents. Much of the dirt is hard clay, which is laborious to break down and may not yield anything in the end.

“But there could be some cool stuff in there, bone fragments or toes or teeth,” she says. “The mud clumps are like giant Easter eggs and you don’t know what might be inside.”

Terry is also interested in studying the mammoth’s stable isotopes, atoms that have the same number of protons and electrons but a different number of neutrons. As their name implies, stable isotopes do not decay into other elements. Carbon isotopes can provide information about the animals’ diet, in terms of plants it likely ate, while oxygen isotopes can shed light on an animal’s migration history.

“The isotopes, recorded in the tooth enamel, are like a tape recorder, giving a chronology of an animal’s life,” she says.

More Bones on Campus

With support from the OSU Research Office, Davis purchased a ground-penetrating radar system last spring to detect objects under the surface without disturbing them. Researchers have used the equipment to follow traces of the ancient stream channel as it led out of the stadium and up toward the parking lot. The radar indicated some additional large hard objects in the bottom of the channel, suggesting the presence of more animal bones.

Davis hopes to develop a course that would allow students to use the equipment on campus and beyond, perhaps in open fields or agricultural lands where excavation would be possible.

“It’s like being a detective,” Davis says. “We have clues that there may be more mammoths to find at Oregon State, and we have lots of expertise here on our campus to help us do so. That provides a great opportunity for us and our students to make wonderful discoveries in the coming years.”