A strange object discovered in a San Mateo County creek has given scientists a rare glimpse into the Bay Area’s Ice Age past. the discovery happened during a field survey at a Midpeninsula Regional Open Space District preserve, where Brigid Lynch, a geomorphologist with Balance Hydrologics, was working on a habitat enhancement project for the threatened California red-legged frog.
At first, the object looked like an oddly shaped rock. However, it was an exceptionally preserved fossilized tooth from an adult Pacific mastodon, an enormous Ice Age mammal that once roamed what is now California. Researchers believe the specimen could be around 10,000 years old, though carbon dating will be used to determine its exact age.
A remarkably preserved discovery
The tooth was examined by paleontologists, who identified it as belonging to Mammut pacificus, or the Pacific mastodon. Wayne Thompson, a paleontologist and owner of Pacific Paleontology, described the tooth as being in “immaculate condition”. He said it is the most complete mastodon molar from the area that he has seen and the most spectacular mastodon molar he has encountered.
Pacific mastodons are distinguished from American mastodons by features including narrower teeth, thicker leg bones and differences in their tusks. Researchers believe their range included present-day California, Oregon, the northern Rocky Mountain region and parts of Mexico.
The ancient Bay Area
According to the Midpeninsula Regional Open Space, the animal lived during the Pleistocene epoch, which began roughly 2.5 million years ago and ended around 11,700 years ago. The landscape would have supported a striking mix of animals. Mastodons were browsers, using their trunks to strip leaves, soft shoots and fruits from woody plants. They shared the broader region with Columbian mammoths, Jefferson’s ground sloths and western camels. Some animals familiar to Californians today were also part of the ancient ecosystem, including mountain lions, bobcats, coyotes and tule elk. Saber-toothed cats and dire wolves also lived in the region.
What happens to the fossil now?
Midpen has donated the tooth to Stanford University’s Doerr School of Sustainability for further study. Researchers plan to carbon-date the specimen and create a 3D scan, then print a replica for Midpen to use in public education and outreach. For Lynch, the discovery was an extraordinary moment during what began as a modern conservation project. “As a geologist, I’ve gone out and seen stuff in the field, but definitely nothing as exciting as this,” she said.
