Phylogeny and systematic revision of Eocene Cricetidae (Rodentia, Mammalia) from Central and East Asia: on the origin of cricetid rodents

The origin of the Cricetidae and the relationships among earliest species from Central and East Asia are still disputed. The taxonomic status of some Eocene cricetid taxa is also doubtful. A parsimony analysis based on 65 cranial and dental characters and including 22 early Myomorpha was performed to elucidate these issues. As a result, the North American Elymys, known as the first Myodonta, belongs to dipodoid rodents, although it shares a suite of characters with the first cricetids. This implies that the split between dipodoids and muroids occurred in North America during the early middle Eocene, as previously supposed. The disputed Simimys and Nonomys could constitute an early dipodoid radiation. It appears that the earliest offshoot of the cricetid clade is the Asian genus Palasiomys. This taxon has a more advanced cricetid plan than contemporaneous dipodoids. The genus Raricricetodon no longer exists here because it is polyphyletic; the species are included in Palasiomys (P. minor, P. trapezius) and Pappocricetodon (P. zhongtiaensis). The genus Pappocricetodon displays a complete cricetid plan associated with both the loss of P⁴ and the development of an anterocone on M¹. The disputed genera Eocricetodon and Oxynocricetodon characterize the beginning of the Oligocene radiations of Eucricetodontinae throughout the Holarctic continents.