Strange 8.5-inch object found in California creek turns out to be 10,000-year-old mastodon tooth; scientist says, “I had chills and shivers up and down my spine”

A researcher in California was out for a routine field survey in a San Mateo County creek looking for an appropriate habitat for a threatened frog. But she was stunned when she stumbled upon an extraordinary discovery from the Ice Age, a remarkably preserved Pacific mastodon molar believed to be at least 10,000 years old, reports The Daily Beast. The discovery has shocked a paleontologist who said he had "hills and shivers up and down his spine"

What initially appeared to be an oddly shaped rock nestled in the dirt to geomorphologist Brigid Lynch actually turned out to be the giant 10,000-year-old tooth of an extinct Ice Age mammal. Paleontologists said the fossil is exceptionally complete and could provide scientists with a rare glimpse into the ancient ecosystems of California, when enormous Ice Age mammals roamed the region.


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The discovery was made this summer during field surveys in a preserve managed by the Midpeninsula Regional Open Space District, commonly known as Midpen. The fossil has since been donated to Stanford University for further study.

Paleontologist says the tooth gave him chills

What has made the discovery important and interesting is the condition of the fossil. Paleontologist Wayne Thompson, owner of Pacific Paleontology, described it as an extraordinary specimen and said it could help researchers understand the prehistoric animals that once inhabited the region.

“It's the most complete mastodon molar from our area, and the most spectacular mastodon molar that I've ever seen,” Thompson said. “I had chills and shivers up and down my spine.” He added: “It’s another puzzle in the Ice Age saga that we can put into place.”

As of now, the fossil's exact location has not been disclosed. Midpen said it does not permit visitors to search for fossils in waterways, making the discovery a particularly unusual result of scientific fieldwork rather than a recreational fossil hunt.

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Researcher was searching for frog habitat when she found the fossil

While surveying the creek bed, Brigid Lynch noticed an unusual object in the dirt. At the first glance, it did not look like the remains of a giant prehistoric animal.

“As a geologist, I've gone out and seen stuff in the field, but definitely nothing as exciting as this,” Lynch said.

The object was later identified as an intact molar belonging to an adult Pacific mastodon. According to reports, what Lynch found was a molar from a Pacific mastodon, a hairy ancestor of today’s elephant that used to roam the West Coast during the Pleistocene epoch. That period began around 2.5 million years ago and ended just 11,700 years ago.

The tooth measures about 8.5 inches long, 7 inches deep and 3 inches wide, according to Midpen.

All about Mammut pacificus that lived in California thousands of years ago

The animal that left behind the tooth was a Pacific mastodon, scientifically known as Mammut pacificus. The species was officially recognized in 2019 and is different from the better-known American mastodon. Researchers distinguish the Pacific mastodon by features including narrower teeth, thicker leg bones and different tusks.

Pacific mastodons once lived across a large part of western North America, including California, Oregon, the northern Rocky Mountains and parts of Mexico. They belonged to the Pleistocene world, an era that began roughly 2.5 million years ago and ended about 11,700 years ago.

Unlike mammoths, which primarily grazed on grasses, mastodons were browsers. Their teeth were adapted for crushing and processing vegetation such as twigs, leaves, soft shoots and fruits from woody plants.

Stanford will carbon-date and 3-D scan the tooth

The ancient tooth has been donated to Stanford University's Doerr School of Sustainability, where researchers will conduct additional tests. Scientists are planning to use carbon dating to determine its exact age and create a 3-D scan of the fossil. A 3-D copy will also be produced for Midpen's educational and public outreach work.

“Fossils are our only opportunity to see into past biodiversity,” Christine Garcia, curator and manager of Stanford's Geoscience Specimen Collection, said.

Garcia said fossils can help researchers understand ancient wildlife and ecosystems and “help us make better predictions and better decisions about how to help our ecosystems and biodiversity thrive into the future.”

The latest discovery follows another unusual Pacific mastodon find in California. In 2023, a woman walking along Rio Del Mar State Beach near Santa Cruz spotted what appeared to be a piece of driftwood. After posting a photograph online, she was connected with Thompson, who identified the object as a Pacific mastodon molar.

That fossil was subsequently added to the Santa Cruz Museum of Natural History's collection. The latest San Mateo County discovery is even more remarkable because of its exceptional preservation and completeness, giving scientists another rare opportunity to investigate a vanished chapter of California's natural history.