Total-evidence phylogeny reveals recent crown group radiation and biogeographical history of hamsters

The systematics of extant hamsters (Cricetinae) have been increasingly clarified, due to advances in molecular phylogenetics. In contrast, their relationships with their fossil relatives have remained relatively unclear. Furthermore, studies on the biogeographical history and divergence times of the main groups of extant hamsters have so far been limited to molecular phylogenies and node dating approaches.

Here, we present the first 'total-evidence' analysis of hamsters that combines extinct and extant taxa, based on a comprehensive dataset covering 82 species (~ 75% of the total known diversity of 109 species). We performed a relaxed-clock Bayesian phylogenetic reconstruction and used the resulting tip-dated tree to estimate ancestral geographic ranges. Our results confirm '†Kowalskia' as a synonym of †Neocricetodon, support the previously suggested non-monophyly of †Allocricetus, †Cricetulodon, and '†Cricetinus' and reveal several fossil taxa as potential close relatives of the crown group. We recover a Pliocene origin of the crown hamsters, considerably younger than previous estimates of a late/middle Miocene origin. Our biogeographic reconstructions suggest a Central and Eastern European origin of the entire group, with crown hamsters emerging in the region around the Black Sea and the Eastern Mediterranean. Subsequent dispersal events into Western Europe and East Central Asia may be linked to the expansion of open vegetation.

Based on a total-evidence phylogenetic reconstruction, we highlight necessary taxonomical revisions for several fossil cricetine taxa and explore the biogeographical evolution of the group. Importantly, our estimated divergence dates reveal a substantially younger group of crown hamsters than previously assumed.