A geologist surveying frog habitat found the most complete Pacific mastodon molar in the area

The Pacific mastodon has only been recognized as a species since 2019 ^[13]. What separates it from the American mastodon is a set of skeletal details: a narrower third molar, thicker hind-leg bones, and lower-jaw tusks that are sometimes absent, according to the Royal Alberta Museum as cited by Live Science ^[14]. That list gives teeth real diagnostic weight. If this specimen is a third molar, it is the same element the 2019 species split relies on. It came out of the creek bed intact at roughly 8.5 inches long and 3 inches wide ^[17].

The age estimate is preliminary, and the two published accounts state it differently. Discover reports that paleontologists put the tooth at about 10,000 years old ^[8]. Live Science writes that it dates to at least 10,000 years ago, around when the Pacific mastodon is thought to have gone extinct ^[9]. "At least" is a floor and "about" is a point estimate. Both accounts put the end of the Pleistocene at 11,700 years ago ^[15][16], so a flat 10,000-year date would place this animal some 1,700 years into the Holocene ^[18]. The two accounts also disagree on when the epoch began: 2.5 million years ago in Discover ^[16], 2.6 million in Live Science ^[15].

Researchers at Stanford hope to determine the age more accurately using carbon dating ^[11]. The donation puts a field find into a curated collection with a named custodian, Christine Garcia, curator and manager of the Geoscience Specimen Collection at Stanford ^[19]. "Fossils are our only opportunity to see into past biodiversity," Garcia said in the Midpen release ^[19].

The tooth fixes a single animal at a single site. It does not say how many mastodons used that drainage, or when the local population ended. The work behind the superlative is a preliminary analysis by Pacific Paleontology, the consulting firm Wayne Thompson runs ^[4]. The claim is also regional in its own terms: the most complete mastodon molar from the area ^[5].

Lynch, a geomorphologist with the hydrology consulting firm Balance Hydrologics, was surveying the creek this summer when she noticed the shape ^[1]. "As a geologist, I've gone out and seen stuff in the field, but definitely nothing as exciting as this," Lynch said in the Midpen statement ^[7]. Thompson's account of the specimen, in the same statement: "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. I had chills and shivers up and down my spine." ^[5] He also called it "another puzzle in the Ice Age saga that we can put into place" ^[6]. Midpen plans to use a 3D copy of the molar for public outreach and education ^[12].