For decades, paleontologists assumed mastodons - the shaggy, elephant-like relatives that once roamed North America - were a relatively uniform species with a broad range. A new study published in Science Advances is rewriting that narrative, showing that climate change repeatedly drove mastodons to expand, contract, and diversify in ways more complex than previously understood.
The research team, led by Emil Karpinski of Harvard Medical School and Hendrik Poinar of McMaster University, analyzed mitochondrial genomes from seven mastodons spanning North America’s eastern seaboard to the Pacific Northwest. By sequencing DNA from teeth and bones dating back hundreds of thousands of years, the team reconstructed patterns of dispersal that aligned closely with the waxing and waning of Ice Age glaciers.
One of the most striking findings comes from Oregon’s Tualatin mastodon. Identified morphologically as a Pacific mastodon (Mammut pacificus), its DNA confirmed this classification and expanded the known range of the species northward into Oregon and even Alberta, Canada. This challenges earlier ideas that Pacific mastodons were confined largely to California and parts of the American West. The genetic data suggest these animals may have overlapped with American mastodons (M. americanum) in Alberta, opening the possibility of hybridization between the two.
In Mexico, the researchers found evidence of a highly divergent mastodon lineage, tentatively linked to the Pacific mastodon but genetically distinct enough that it could represent an entirely new, cryptic species. This finding pushes the southern boundary of mastodon diversity and underscores how little is known about populations that lived in warmer, less fossil-friendly environments.
On the opposite side of the continent, mastodons from Nova Scotia and the Georges Bank revealed an equally surprising story. Instead of belonging to a single lineage, their DNA showed at least three distinct dispersal events into the region during different interglacial periods. One specimen from Little Narrows, Nova Scotia, may even represent the oldest mastodon sequenced to date, with an estimated age of up to 471,000 years. These results suggest that eastern North America was repeatedly colonized and abandoned as glaciers advanced and retreated, making it a dynamic frontier for mastodon populations.
Taken together, the study paints a picture of mastodons as climate-sensitive migrants, repeatedly shifting their ranges in response to environmental change. Unlike static, regionally confined species, mastodons appear to have been opportunistic, moving northward during warmer periods and withdrawing southward when ice sheets returned. This ebb and flow produced genetic divergences that sometimes rose to the level of speciation.
The work also highlights the power of ancient DNA to resolve debates that morphology alone cannot. For example, earlier studies had questioned whether Pacific mastodons were truly a distinct species or simply a morphological variant of the American mastodon. By tying genetic clades to clearly identified specimens, the new study confirms that the Pacific mastodon was indeed a separate lineage, while hinting that Mexico’s fossils may add a third to the roster.
Beyond clarifying taxonomy, the findings carry implications for understanding how megafauna respond to climate stress. “These dispersal and extinction patterns show that mastodons were highly sensitive to glacial cycles,” the authors write. Their repeated expansions into marginal regions - followed by local extinctions - illustrate both resilience and vulnerability. In the end, mastodons, like mammoths and other Pleistocene giants, failed to survive the climatic upheavals and human pressures of the late Ice Age.
Still, the research underscores just how dynamic their evolutionary history was. What once looked like a single species marching steadily across North America now appears to have been a shifting mosaic of lineages, each adapting - or failing to adapt - to the ice age’s relentless cycles.
Written with the help of a news-analysis system.