Archaeology

Expanding the Known Range of the Pacific Mastodon

Andrew Boehm stands next to a bison skeleton on display. He smiles at the camera.

Dr. Andrew Boehm stands in front of a bison skeleton in the Muséum national d’Histoire naturelle in Paris, France.

The Tualatin mastodon, perhaps the most well-known mastodon fossil in Oregon, is at the forefront of a new species classification.

In a new paper, museum zooarchaeologist Dr. Andrew Boehm and a team of international researchers examine the mastodon fossils displayed in the Tualatin Public Library and reclassify the skeleton as belonging to the Pacific mastodon. This is the first Oregon specimen to be identified as the new species.

The Pacific mastodon (Mammut pacificus) was first described as a distinct species from the American mastodon (Mammut americanum) in 2019. The new analysis, published in January in the open-access Journal PeerJ, includes contributions from researchers from Canada, the United States, and Mexico and expands the known range of the Pacific mastodon species by re-examining fossils previously thought to be M. americanum.

A map of North America. Dots across the central and eastern United States are blue, indicating fossils found of the American Mastodon. Dots on the West Coast and in western Canada and central Mexico are red, indicating locations of Pacific mastodon fossils.

Late Pleistocene distribution map of Mammut pacificus and Mammut americanum. Credit Dooley et al., 2025.

METHODS: The team assigned a specimen to M.pacificus based on criteria laid out in the initial description of the species—a particular width ratio in the leg bones, the presence of mandibular tusks, and a size range for molars are all examples.

The Tualatin mastodon, recovered from a marsh in 1962, has a molar and left femur that are more typical of the new mastodon species than M. americanum, leading the team to believe the mastodon belongs to M. pacificus.

RESULTS: In addition to the Tualatin mastodon, the team of scientists applied these criteria to mastodon fossils from across the United States as well as Canada and Mexico. The results expand the known range of the Pacific mastodon south to include Jalisco and Hidalgo, Mexico, and north to to include Alberta, Canada.

The paper also suggests the two species of mastodons had geographic overlap. Further research is needed to know if the species lived in the same places at the same time.