A creek nestled in the San Mateo County hills recently gave up a secret it has held since the Ice Age: the remarkably well-preserved tooth of a mastodon that once lumbered through the Bay Area's redwood forests.
Brigid Lynch, a geomorphologist, made the discovery while surveying a Midpeninsula Regional Open Space District preserve as part of a habitat restoration project for the threatened California red-legged frog.
Lynch said she initially thought it was just an odd rock. But when she showed it to a paleontologist, they identified it as an intact molar from an adult Pacific mastodon, a massive elephant-like animal that went extinct about 11,000 years ago.
"As a geologist, I've gone out and seen stuff in the field," Lynch said in a statement Wednesday. "But definitely nothing as exciting as this."
The tooth is about 10,000 years old, though researchers at Stanford University's Doerr School of Sustainability plan to use carbon dating to determine its precise age.
Wayne Thompson, a paleontologist and owner of Pacific Paleontology, said the tooth is the most complete mastodon molar found in the region. He said it's the most spectacular thing he's ever laid his eyes on.
"The tooth itself is in immaculate condition," Thompson said. "I had chills and shivers up and down my spine. It's another puzzle in the Ice Age saga that we can put into place."
The Pacific mastodon was only recently recognized as a species different from its better-known American cousin east of the Rockies. The major differences: Pacific mastodons have narrower teeth, thicker leg bones and different tusks. And their range was wide, stretching from what is now California, Oregon, the northern Rocky Mountain region and on down to parts of Mexico.
The now-extinct species roamed the Bay Area during the Pleistocene epoch, which began about 2.5 million years ago and ended with their extinction about 11,700 years ago, according to the regional open space district. But unlike grass-eating mammoths - a similar, more well-known species - mastodons were "browsers," using their long trunks to strip leaves, shoots and fruit from plants much like elephants today.
The mastodon that lost its tooth in that creek bed would have interacted with many modern-day species: mountain lions, bobcats, coyotes and badgers. But their neighbors were also now-extinct species, such as saber-toothed cats, dire wolves, Columbian mammoths, western camels and giants Jefferson's ground sloths.
Midpen donated the tooth to Stanford for further study, and researchers told the district they plan to create a 3D scan and printed replica for public education purposes.
"Fossils are our only opportunity to see into past biodiversity," said Christine Garcia, curator and manager of Stanford's Geoscience Specimen Collection. Studying them, she said, can help scientists understand ancient ecosystems and make better decisions about protecting biodiversity.
For Midpen biologist Matt Sharp Chaney, the discovery could help researchers find out when Pacific mastodons went extinct, data that scientists could use to prevent today's species from meeting the same fate.
"That mastodons were out here in the same landscape that we're in today really drives home how important the work that we do is to keep species from winking out forever," Chaney said. "The presence of mastodons wasn't that long ago, in geologic time."
In its statement Wednesday, Midpen did not disclose exactly where and when the tooth was discovered.
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This article originally published at She was looking for frogs in the San Mateo hills. Then she stumbled upon an Ice Age mystery.