Science2 publishers3 min readPublished
A geologist surveying frog habitat found the most complete Pacific mastodon molar in the area
Brigid Lynch took it for an oddly shaped rock in a San Mateo County creek bed. Midpen has since donated the tooth to Stanford, where a radiocarbon date will test a preliminary estimate of about 10,000 years.
The Scientist · Science desk
What happened
- She was there for a habitat enhancement project supporting the threatened California red-legged frog inside a Midpeninsula Regional Open Space preserve in San Mateo County.
- ABC reports the tooth measures about 8.5 inches long, 3 inches wide and about 7 inches deep, and paleontologists describe its condition as excellent.
- Midpen donated the molar to Stanford University's Doerr School of Sustainability in July, according to the Los Angeles Times.
Compiled by The ScientistSomething wrong?How this is made
Why it matters
- capability Because the difference between the two mastodon species includes a narrower third molar, an unbroken crown can carry a species assignment on morphology; worn or fragmentary teeth from the same region often leave that question open.
- contradiction "About 10,000 years" and "at least 10,000 years" are not the same claim, so the pending Stanford date decides whether this animal died inside the Pleistocene or after the 11,700-year boundary the same accounts use.
- precedent A permitted frog-habitat job by a private consultancy fed a specimen through a public agency into a university collection.
- constraint A single tooth supports almost no inference about how common mastodons were on the peninsula, and the superlative behind the coverage rests on one consulting firm's preliminary look.
The Pacific mastodon has only been recognized as a species since 2019 [14]. 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 [15]. 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 [8].
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 [9]. Live Science writes that it dates to at least 10,000 years ago, around when the Pacific mastodon is thought to have gone extinct [10]. "At least" is a floor and "about" is a point estimate. Both accounts put the end of the Pleistocene at 11,700 years ago [16][17], 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 [17], 2.6 million in Live Science [16].
Researchers at Stanford hope to determine the age more accurately using carbon dating [12]. 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 [13].
What to watch
- The radiocarbon result from Stanford, and whether it lands before or after the 11,700-year Pleistocene boundary both accounts cite.
- A published description of the specimen, including which molar position it occupies, since the species distinction rests on the third molar.
- Whether the 3D scan is released in a form other researchers can measure rather than only used for outreach.