When the researchers analyzed genetic material from the bones, teeth and tusks of 33 American mastodons, they found they traveled wide distances. Mastodons liked wet, warm and forest habitats. During warm periods, they traveled north to areas once covered by ice. During icy periods, they headed south.

“These weren’t stationary populations. The data show there was constant movement back and forth,” says study co-author Hendrik Poinar, an evolutionary geneticist who directs McMaster University’s McMaster Ancient DNA Center, in a news release.

Once they went north, the intrepid mastodons didn’t necessarily thrive. The genetic material points to die-offs when once-cold regions froze over again. New groups would strike north during subsequent cold periods and suffer the same fate.

The mastodons that expanded north were less genetically diverse, too. That made them vulnerable to extinction, the researchers say — and points to potential problems for modern-day mammals, such as moose and beavers, that have widened their range due to climate change.

Take the brown bear, whose habitat is pushing north into the Arctic as the region becomes warmer and warmer. Like the mastodons, they find sustenance in a new but welcoming habitat. But that benefit can be “limited,” warns Ross McPhee, a curator at the American Museum of Natural History and one of the study’s co-authors.

If modern mammals push north without genetic diversity in southern species, the authors write, they could be in danger if southern populations are lost. Perhaps better understanding how ancient mammals like mastodons moved could help researchers better understand how to ensure today’s animals survive the effects of human-caused climate change.