Ancient DNA has been useful in reconciling deep evolutionary relationships and responses to ecological changes in elephants and their relatives. In new research, scientists sequenced the mitochondrial genomes of several mastodons: five from Nova Scotia and the eastern seaboard, one of which may date to approximately 500,000 years ago, and for the first time, a unique specimen of a Pacific mastodon from Tualatin, Oregon, in addition to a partial mitochondrial genome from Northern Ontario. Their results show that Pacific mastodons fall within a deeply divergent mitochondrial group, extending the range of this species into western Canada and potentially Mexico. The authors also found evidence for at least three separate expansion events into northeastern coastal regions and identified two new mastodon groups, which contain distinct but geographically colocalized specimens.
An adult mastodon (Mammut sp.) consuming a spruce branch set against a backdrop illustrating their cyclical continental migrations linked to climate fluctuations. At least two species of mastodons roamed North America during the Middle and Late Pleistocene: the American mastodon, stretching from the eastern seaboard to central parts of the continent, and the Pacific mastodon from central Alberta through California. Image credit: Kathryn Killackey.
Mastodons were initially split into numerous separate species but later consolidated back into a single one: the American mastodon (Mammut americanum).
More recently, this classification has been revised to potentially include at least two distinct species: the American mastodon and the Pacific mastodon (Mammut pacificus), although a debate over the split has persisted.
The genetic analyses confirm the Pacific mastodons belong to a very old, well-established and separate genetic branch, with a range that extended much farther than previously believed — reaching deep into the Pacific Northwest, possibly south to Mexico, and as far north as Alberta.
Interestingly, Alberta appears to have been a ‘hot spot,’ where Pacific and American mastodons congregated, expanded northward and may have interbred.
The East Coast and Northern Ontario specimens revealed two new and distinct genetic groups, known as clades, of mastodons living in the same region but at different times.
The eastern species were surprisingly diverse, arriving in distinct waves of migration at least three times — a pattern driven by repeated cycles of climate warming, leading to glacial melting and the opening of new territory for northward expansion.
When climate cooled and glaciers expanded, mastodons were driven south or went locally extinct.
“The data shift our view of the region today known as Alberta and the north more generally, from a marginal roaming ground to a repeatedly occupied migratory corridor and significant landscape for mastodons with possible interbreeding,” said Dr. Hendrik Poinar, director of the McMaster Ancient DNA Centre at McMaster University.
The researchers also pinpointed a mysterious and genetically distinct Mexican mastodon lineage, which they believe could be a deeper branch of the western species the Pacific mastodon pacificus or possibly an entirely new, third mastodon species.
The mastodon was among the largest living land animals on Earth during the Ice Age, roaming from Beringia (present-day Alaska and the Yukon) east to Nova Scotia and south to Central Mexico.
They were primarily browsers, living in swampy settings, eating shrubs and low-hanging tree branches, and occupied a very different habitant from their distant cousins, the Ice Age iconic woolly mammoths which roamed on open grasslands and tundra.
“This study represents several firsts which includes our work on the Pacific mastodon,” said Emil Karpinski, a researcher at the Harvard Medical School.
“It also poses many new questions. For example, how did these distant species of mastodon interact in Alberta?”
“Did they compete for resources, or did they interbreed as our lab has previously shown for mammoths?”
“These new findings, combined with those reported in the team’s 2020 study, create a much more complete picture of how mastodons moved and diversified across North America, helping conservationists today prepare for an ever warming artic and northern migrating species,” the scientists said.
Their paper was published September 12, 2025 in the journal Science Advances.
_____
Emil Karpinski et al. 2025. Repeated climate-driven dispersal and speciation in peripheral populations of Pleistocene mastodons. Science Advances 11 (37); doi: 10.1126/sciadv.adw2240