A fossilised tooth found in a San Mateo County creek has been identified as an exceptionally well-preserved molar from an adult Pacific mastodon that lived at least 10,000 years ago.
The discovery was made this summer by geomorphologist Brigid Lynch, who was carrying out field surveys linked to a habitat improvement project for the threatened California red-legged frog.
Lynch initially believed the object, partly submerged in a creek in a Midpeninsula Regional Open Space District preserve, was an unusually shaped rock. Paleontologists later confirmed it was an intact Pacific mastodon molar.
The tooth measures about 8.5in long, 7in deep and 3in wide. Wayne Thompson, a paleontologist and owner of Pacific Paleontology, described it as the most complete mastodon molar found in the area.
“The tooth itself is in immaculate condition. It’s the most complete mastodon molar from our area, and the most spectacular mastodon molar that I’ve ever seen,” he 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.”
Lynch said: “As a geologist, I’ve gone out and seen stuff in the field, but definitely nothing as exciting as this.”
The exact location of the find has not been disclosed. Midpen said it did not want visitors searching waterways for fossils, and described the site only as a creek in the redwood forests of San Mateo County.
Pacific mastodons were large, hairy relatives of modern elephants which inhabited parts of California, Oregon, the northern Rocky Mountains and Mexico during the Pleistocene epoch. They became extinct about 11,700 years ago.
The species, known scientifically as Mammut pacificus, was only formally recognised as distinct from the better-known American mastodon in 2019. Pacific mastodons had narrower teeth, thicker leg bones and differently shaped tusks.
Unlike mammoths, which primarily grazed on grasses, mastodons were browsers. They used their trunks to strip leaves, shoots and fruit from woody plants.
The animals lived alongside other now-extinct giants in ancient California, including Columbian mammoths, western camels and bison-sized Jefferson’s ground sloths.
Midpeninsula Regional Open Space District, which manages 27 preserves covering more than 70,000 acres across the Bay Area, donated the fossil to Stanford University’s Doerr School of Sustainability in July.
Researchers will use carbon dating to establish the tooth’s precise age and will produce a three-dimensional scan and printed replica for public education.
Christine Garcia, curator and manager of Stanford’s Geoscience Specimen Collection, said fossils offered a rare way to examine past biodiversity and the ecosystems in which extinct animals lived.
Midpen biologist Matt Sharp Chaney said the discovery also underlined the importance of conservation work in the region.
“The fact 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,” he said.
