For the majority of the twentieth century, Ice Age mastodons were considered a single species that inhabited areas across North America.
Now, that all changes thanks to new genetic research that challenges this perspective, showing that climate change contributed to a more intricate evolutionary history for these lost giants, marked by the emergence of multiple lineages and repeated migration patterns.
A study recently published in Science Advances by researchers from McMaster University and Harvard reconstructs mitochondrial genomes from mastodon fossils spanning hundreds of thousands of years. The findings suggest that mastodons were a more diverse group than previously thought, exhibiting broad migratory ranges and possible interbreeding, driven by climate change.
Decoding Ancient DNA
The team analyzed well-preserved teeth, tusks, and bone specimens from several regions, including five fossils from Nova Scotia, a partial genome from northern Ontario, and, for the first time, DNA from a Pacific mastodon specimen found in Tualatin, Oregon. By assembling degraded DNA fragments, researchers were able to reconstruct genetic profiles of populations that are now extinct.
These results contribute important new evidence to ongoing debates about mastodon classification. Mastodons were historically divided into multiple species before being grouped under the single species Mammut americanum, but recent findings have reopened discussion regarding this classification. The study provides support for distinguishing the Pacific form, Mammut pacificus, as a separate lineage, suggesting a greater diversity among the species than previously recognized.
A Fusion of Lineages
The analysis indicates that Pacific mastodons represent a distinct and ancient genetic branch, with a migratory range that extended beyond the Pacific coast into the Pacific Northwest, Alberta, and possibly as far south as Mexico.
Alberta is identified as a region where American and Pacific mastodons overlapped, expanded their migration northward, and may have interbred. This evidence suggests that Alberta and adjacent northern areas functioned as important migratory corridors rather than marginal habitats.
Specimens from Nova Scotia and Ontario reveal two genetically distinct mastodon lineages that occupied the same region at different times. Each of these lineages reflects a separate population, linked to specific migration waves that occurred during warming periods and glacial melting, which made new regions accessible. When the climate cooled again, these genetically distinct groups either shifted their range southward or disappeared entirely.
The study also identifies a genetically distinct Mexican mastodon lineage, which may represent a separate branch within Mammut pacificus or a potential third species of mastodon. This finding adds further complexity to the understanding of mastodon evolutionary relationships.
Reshaping the Family Tree
Mastodons occupied a broad range of land, from Alaska and Yukon to Nova Scotia, and as far south as central Mexico. In contrast to woolly mammoths, which grazed on the open tundra, mastodons were known to inhabit swampy forests, primarily feeding on shrubs and tree branches.
Tracing the evolution of mastodons provides a direct example of how large mammals responded to ancient climate fluctuations. The evidence suggests that mastodons recolonized or migrated out of northern regions as warming and glacial cycles shifted. These trends could potentially be applied to study how current species might respond to modern climate change scenarios.
“These findings create a much more complete picture of how mastodons moved and diversified across North America,” said lead author Emil Karpinski, now at Harvard Medical School. “It also poses new questions. Did these distant species of mastodon interact in Alberta? Did they compete for resources, or did they interbreed as our lab has shown for mammoths?”
Lessons From an Ice Age Giant
The research builds on a 2020 study from the same team. While this analysis utilizes mitochondrial DNA, researchers suggest that sequencing nuclear genomes could provide an even more comprehensive picture of interbreeding and species boundaries.
These findings recast mastodons as a branching, migratory lineage shaped by climate, rather than a single, uniform Ice Age species. The study also demonstrates the value of ancient DNA in reconstructing evolutionary history and understanding adaptation to environmental change.
Although mastodons are extinct, their genetic legacy informs current scientific understanding of survival, extinction, and adaptation in the context of climate change. As the Arctic experiences rapid warming, the evolutionary history of mastodons offers insight into the potential consequences for modern species.
Austin Burgess is a writer and researcher with a background in sales, marketing, and data analytics. He holds a Master of Business Administration and a Bachelor of Science in Business Administration, along with a certification in Data Analytics. His work combines analytical training with a focus on emerging science, aerospace, and astronomical research.