For the majority of the twentieth century, Ice Age mastodons were considered a single species that inhabited areas across North America. Decoding Ancient DNAThe 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. Alberta is identified as a region where American and Pacific mastodons overlapped, expanded their migration northward, and may have interbred. This finding adds further complexity to the understanding of mastodon evolutionary relationships. These findings recast mastodons as a branching, migratory lineage shaped by climate, rather than a single, uniform Ice Age species.