{"id":52396,"date":"2026-10-21T07:31:00","date_gmt":"2026-10-21T11:31:00","guid":{"rendered":"https:\/\/www.ecoticias.com\/en\/?p=52396"},"modified":"2026-10-20T09:08:32","modified_gmt":"2026-10-20T13:08:32","slug":"in-a-san-mateo-county-creek-a-geomorphologist-surveying-habitat-for-threatened-california-red-legged-frogs-found-an-intact-pacific-mastodon-molar-a-species-only-named-in-2019-and-stanford-plans-to","status":"publish","type":"post","link":"https:\/\/www.ecoticias.com\/en\/in-a-san-mateo-county-creek-a-geomorphologist-surveying-habitat-for-threatened-california-red-legged-frogs-found-an-intact-pacific-mastodon-molar-a-species-only-named-in-2019-and-stanford-plans-to\/52396\/","title":{"rendered":"In a San Mateo County creek, a geomorphologist surveying habitat for threatened California red-legged frogs found an intact Pacific mastodon molar, a species only named in 2019, and Stanford plans to carbon date it"},"content":{"rendered":"\n

A geomorphologist surveying a creek in a San Mateo County preserve for threatened California red-legged frogs this summer found an intact Pacific mastodon molar from an adult animal, the Midpeninsula Regional Open Space District, known as Midpen, announced on Sept. 9, 2026<\/a>. Stanford University plans to carbon date the tooth to learn its exact age.<\/p>\n\n\n\n

Brigid Lynch, a geomorphologist with Balance Hydrologics, at first took it for an oddly shaped rock in the water, until paleontologists confirmed what it was. “As a geologist, I’ve gone out and seen stuff in the field, but definitely nothing as exciting as this,” she said.<\/p>\n\n\n\n

An oddly shaped rock in a frog creek<\/h2>\n\n\n\n

The surveys were part of a Midpen habitat enhancement project for the frog. Lynch and her colleagues contacted Garret Trask, senior archaeologist for Stanford Heritage Services, for help identifying and preserving the find, according to Stanford University Libraries<\/a>. Midpen does not name the preserve beyond the county.<\/p>\n\n\n\n

Wayne Thompson, a paleontologist and owner of Pacific Paleontology, said the tooth is in immaculate condition, the most complete mastodon molar from the area and the most spectacular one he has ever seen. Stanford calls it an “enormous molar,” though neither Midpen nor Stanford has published its measurements or weight.<\/p>\n\n\n\n

A mastodon species named in 2019<\/h2>\n\n\n\n

The Pacific mastodon, Mammut pacificus<\/em>, is the newest mastodon species to be recognized. It was described in March 2019 in the journal PeerJ by a team led by Alton C. Dooley Jr. of the Western Science Center in Hemet, California.<\/p>\n\n\n\n

For a long time, scientists lumped all North American mastodons of that era into one species, the American mastodon, Mammut americanum<\/em>, and leaned on fossils from the East, especially Florida, New York, the Midwest and the Great Lakes. Western mastodons, the authors note, had received relatively little attention.<\/p>\n\n\n\n

A reservoir project changed that. Beginning in the early 1990s, construction of Diamond Valley Lake in western Riverside County uncovered more than 700 mastodon bones from more than 100 individuals. The Western animals turned out to have narrower teeth, most clearly in the third molars, six vertebrae in the sacrum, a thicker thighbone and no tusks in the lower jaw at any age. The study concludes that the American mastodon was not present in California.<\/p>\n\n\n\n

Researchers believe the species ranged across what is now California, Oregon, the northern Rocky Mountain region and parts of Mexico, Midpen says. The 2019 study lists specimens from throughout California and from two sites in southern Idaho.<\/p>\n\n\n\n

Browsers among the grazers<\/h2>\n\n\n\n

Mastodons were shorter and stockier, with shorter, straighter tusks, according to the National Park Service<\/a>. Their molars carry pointed cones built for chewing woody browse, meaning twigs, leaves and shoots, while mammoth molars have flat surfaces for grinding grass.<\/p>\n\n\n\n

Midpen says mastodons would wrap their trunks around branches and strip the foliage to feed. Stanford adds that the Pacific mastodon browsed on tree leaves in shaded riparian environments, the strips of woodland along streams.<\/p>\n\n\n\n

\"Illustration
Artist’s illustration of a Pacific mastodon feeding on a tree beside a stream, with the upper left molar marked on the skull and a 9-foot scale next to a human figure. (Image: Haley Grunloh for Midpen)<\/figcaption><\/figure>\n\n\n\n

Meanwhile, ground sloths, mammoths, camels, pronghorn and bison grazed the grassy fields nearby, Stanford says, and Midpen adds that mountain lions and bobcats may have stalked prey alongside saber-toothed cats and dire wolves. Similar Ice Age casts of characters turn up elsewhere in the West, from human footprints beside mammoth tracks at White Sands<\/a> to the American cheetah of the Yukon<\/a>.<\/p>\n\n\n\n

A tooth in the Stanford collection<\/h2>\n\n\n\n

Midpen donated the molar to Stanford University’s Doerr School of Sustainability. It is now held in the Geoscience Specimen Collection, where it is being preserved for carbon dating, 3D imaging and further study. “Fossils are our only opportunity to see into past biodiversity,” said Christine Garcia, curator and manager of the collection.<\/p>\n\n\n\n

\"Midpen
Matt Sharp Chaney of Midpen and Christine Garcia of Stanford hold the mastodon tooth. (Photo: Midpeninsula Regional Open Space District)<\/figcaption><\/figure>\n\n\n\n

A 3D scan by Tony Calavano of the Libraries’ Digital Library Systems and Services department is posted in the Stanford Digital Repository, and Stanford will print a replica for Midpen to use in public outreach.<\/p>\n\n\n\n

Jonathan Payne, the Dorrell William Kirby Professor in Stanford’s Department of Earth and Planetary Sciences, said fossils such as this tooth are critical for understanding what species lived in the area before and during early human occupation. They also help show what a pre-human baseline ecosystem looked like and how parts of it might be restored, he said.<\/p>\n\n\n\n

Habitat work for a threatened frog<\/h2>\n\n\n\n

The California red-legged frog is the largest native frog in the western United States, with females reaching 5.4 inches (138 millimeters), according to the U.S. Fish and Wildlife Service. The agency names habitat loss and alteration, along with non-native species, as the main threats. The frog was listed as threatened in 1996 and, once found in 46 counties, is now known from 35 California counties, though it is still common in the San Francisco Bay Area.<\/p>\n\n\n\n

It spends most of its life in or near streams or stock ponds, where it breeds, and hides from summer heat under rocks, leaf litter or in animal burrows. Each egg mass holds about 300 to 4,000 eggs, but fewer than 1 percent survive the tadpole stage. Amphibians can move in fast once there is water, as one backyard pond dug for frogs<\/a> showed within weeks.<\/p>\n\n\n\n

“That mastodon 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,” said Midpen biologist Matt Sharp Chaney.<\/p>\n\n\n\n

What one tooth cannot tell us<\/h2>\n\n\n\n

Midpen’s headline called the fossil 10,000 years old, but the district also said researchers plan to use carbon dating to determine its exact age. Mastodons roamed the region during the Pleistocene epoch, which began about 2.5 million years ago, and went extinct around 11,700 years ago, Midpen says.<\/p>\n\n\n\n

Radiocarbon dating relies on carbon-14, which living things take in until they die and which then decays into nitrogen-14 with a half-life of about 5,730 years, according to the National Institute of Standards and Technology. NIST says the method has dated objects as old as 60,000 years, and in some cases older. It also helps date sites such as a 13,800-year-old Ice Age camp in Alaska<\/a>.<\/p>\n\n\n\n

One tooth also cannot explain why mastodons disappeared or how this individual died, though Payne says fossils help pin down the timing of extinctions so scientists can learn how species responded to past climate change. Neither Midpen nor Stanford has given the exact spot in the creek, the tooth’s size or anything about the sediment it lay in.<\/p>\n\n\n\n

The Pacific mastodon species was described in PeerJ<\/a>.<\/p>\n\n\n\n

Photo: Balance Hydrologics via Midpeninsula Regional Open Space District<\/p>\n","protected":false},"excerpt":{"rendered":"

A geomorphologist surveying a creek in a San Mateo County preserve for threatened California red-legged frogs this summer found an … <\/p>\n

Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":52393,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8],"tags":[],"class_list":["post-52396","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-science","resize-featured-image"],"_links":{"self":[{"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/posts\/52396","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/comments?post=52396"}],"version-history":[{"count":2,"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/posts\/52396\/revisions"}],"predecessor-version":[{"id":52579,"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/posts\/52396\/revisions\/52579"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/media\/52393"}],"wp:attachment":[{"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/media?parent=52396"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/categories?post=52396"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ecoticias.com\/en\/wp-json\/wp\/v2\/tags?post=52396"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}