A geomorphologist, a scientist who studies how landscapes change over time, was surveying a San Mateo County creek for signs of frog habitat when she spotted what looked like an oddly shaped rock. It was a molar from a Pacific mastodon. The paleontologist brought in to examine it says the specimen is likely between 50,000 and 100,000 years old, far older than the figure circulating in most early reports.
Brigid Lynch, a geomorphologist with Balance Hydrologics, found the tooth in a creek inside a Midpeninsula Regional Open Space District preserve in San Mateo County, California. Her survey was focused on improving habitat for the threatened California red-legged frog. Lynch, describing her years of field experience as a geologist, said she had never encountered anything this exciting.
Wayne Thompson, CEO of Pacific Paleontology, examined the molar and describes its condition as immaculate. Here is what that means: mastodon molars have extremely fragile roots, and most specimens lose those roots after being moved by water. This one still has the majority of its roots intact. Thompson says that tells him the tooth did not travel far from where the animal died.
What the tooth's age actually is
Thompson says most early coverage placed the tooth at roughly 10,000 years old, and that figure is wrong. Based on the sediment layer where the molar was found, he estimates the animal lived between 50,000 and 100,000 years ago. Mastodons went extinct roughly 11,700 years ago, near the close of the last Ice Age. Thompson's reading of the site puts this individual animal much further back.
Mastodons were massive, elephant-like herbivores. They are often confused with woolly mammoths, but the two ate differently. Mammoths grazed on grasses; mastodons browsed on leaves and favored creek and river valleys lined with alder trees. Thompson noted that hundreds of alders still grow along the creek where Lynch found the molar.
Researchers from Stanford University's Doerr School of Sustainability plan to carbon date the molar to pin down its exact age and create a three-dimensional scan to produce a replica. Thompson called a find of this quality quite uncommon. He added that the molar likely emerged from the skull recently, and that the skull, along with the rest of the bones, is probably still buried at the site.