A well-preserved upper left molar belonging to a Pacific mastodon, estimated to be at least 10,000 years old, has been discovered in a creek bed in San Mateo County, California, according to the Midpeninsula Regional Open Space District. Field researchers identified the prehistoric fossil during habitat improvement work, and experts describe the specimen as the most complete mastodon molar found in the San Francisco Bay Area.
Pacific Mastodon Molar Discovered in San Mateo County
Field Discovery Along a Bay Area Creek Bed
Brigid Lynch, a geomorphologist with Balance Hydrologics, found the fossil while conducting field surveys for a Midpeninsula Regional Open Space District project aimed at improving habitat for the threatened California red-legged frog, as reported by Open Space. Initially mistaking the object for an unusually shaped rock while examining the creek bed, Lynch photographed the item and continued her survey work. She identified the object as a prehistorical fossil the following day while reviewing her field photographs.
Paleontologist Wayne Thompson, owner of Pacific Paleontology, noted that the tooth is in pristine condition. “It’s the most complete mastodon molar in our area and the most spectacular I’ve ever seen,” Thompson said in a press statement released by Midpen. To protect the site from unauthorized artifact gathering, the Open Space organization decided not to disclose the exact location of the creek.
Anatomy and Habitat of the Pacific Mastodon
The Pacific mastodon is a distinct species recognized separately from the American mastodon following a 2019 anatomical study that identified narrower teeth and a proportionally thicker femur. These large herbivores lived during the Pleistocene epoch, which spanned from hace unos 2,5 millones de años hasta hace 11.700 años, ranging across what is now California, Oregon, the northern Rocky Mountains, and parts of Mexico.
Unlike mammoths, which primarily grazed on grasses, mastodontes were browsers that used their trunks to pull leaves, tender shoots, and woody fruits from large plants. According to Thompson, alders were a favored food source, with remains of the plant occasionally preserved in the mouths and stomachs of mastodonts found in archaeological sites. They shared their environment with other extinct Pleistocene fauna, including saber-toothed cats, dire wolves, Columbian mammoths, western camels, and Jefferson’s ground sloths.
Stanford University Research Plans
The fossil has been donated to the Doerr School of Sustainability at Stanford University. Researchers at the institution plan to subject the molar to carbon dating to establish a precise age, alongside 3D scanning and dietary analysis to shed light on past climates and ecosystems.
“Fossils are our only opportunity to observe the biodiversity of the past,” said Christine Garcia, curator and director of the Geosciences Specimen Collection at Stanford. “We can study the fossils to understand better the past of the Earth, the fauna of the past, and the ecosystem of which they were a part, and to help us make better predictions and make better decisions on how to help our ecosystems and biodiversity thrive in the future.” Following the analysis, Stanford plans to provide a 3D-printed replica of the specimen to Midpen for public education and outreach activities.