Repeated climate-driven dispersal and speciation in peripheral populations of Pleistocene mastodons

Ancient DNA has been useful in reconciling deep evolutionary relationships and responses to ecological changes in proboscideans. Here, we report the sequencing of a mitochondrial genome from a morphologically distinct Pacific mastodon, as well as from six eastern American mastodons with ages that range through the Middle and Late Pleistocene. We show that Pacific mastodons fall within a deeply divergent mitochondrial clade, extending the range of this species into western Canada and potentially Mexico. We also present evidence for at least three discrete expansion events into northeastern coastal regions and identify two new mastodon clades, which contain temporally distinct but geographically colocalized specimens. We integrate these findings with those of previous work into a comprehensive model of Mammut phylogeography.