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New research extends range of Pacific mastodon into eastern Montana

Ice age mastodons, who once roamed the Hemet San Jacinto Valley where the Diamond Valley Reservoir is located, may also have lived as far away as eastern Montana, according to new findings released by Western Science Center and Museum of the Rockies paleontologists.

A new paper from the museums reveals that the Pacific mastodon, Mammut pacificus, described in 2019 from the Pleistocene of California and Idaho, was also found in eastern Montana between 639,000 and 160,000 years ago.

The paper is now available in the open access journal PeerJ; the authors include WSC curator Andrew McDonald; Amy Atwater, collections manager MOR; Alton Dooley, executive director WSC and Charlotte Hohman, undergraduate student at Montana State University.

The paper shows the Pacific mastodon is distinguished in part by third molars that are much narrower than those of other North American mastodons. Specimen MOR 605, a partial skull of a mastodon from Miles City in eastern Montana described in this paper, was assigned to M. pacificus because of its extremely narrow molars. The identification of this jaw as a Pacific mastodon greatly expands the geographic range of M. pacificus more than 500 miles east. MOR 605 was found by a Doeden Construction crew working at a gravel pit and donated to the Museum of the Rockies in 1989.

Determining the new find were the Pacific mastodon fossils sent to the Western Science Museum located at 2345 Searl Parkway in Hemet for study by scientists there.

Other fossils found there include extinct Columbian mammoth, giant ground sloths, giant short-faced bear, horses, camels and musk oxen.

The realization that Pacific mastodons lived in Pleistocene Montana helps scientists paint a better picture of what was happening in this prehistoric environment. Glaciers expanded into Montana several times during the ice age – MOR 605 lived between two glacial episodes, when Montana was somewhat warmer. The Pacific mastodon might have been pushed out of Montana by the next glacial episode as the local climate became colder and drier, but more fossils need to be studied in order to learn more about how the distribution of Pacific mastodon changed as glaciers expanded and contracted.

"The Pacific mastodon embodies how much we still have to learn about the ice age, a slice of time relatively close to ours – much closer than the age of dinosaurs for example," McDonald said. "This discovery of Pacific mastodon in Montana adds to the picture of a dynamic time of great and repeated change, as animals were affected by the comings and goings of glaciers.

"The easternmost occurrence of Mammut pacificus (Proboscidea: Mammutidae), based on a partial skull from eastern Montana, USA" is now available for download on PeerJ's website, http://peerj.com, McDonald said.

Tony Ault can be reached by email at [email protected].

 

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