A new Eocene cylindrodontid rodent from the Erlian Basin (Nei Mongol, China) and its implications for phylogeny and biochronology

We report a new early–middle Eocene cylindrodontid rodent, <i>Gobiocylindrodon ulausuensis</i>, gen. et sp. nov., from the Ula Usu West locality, Erlian Basin, Nei Mongol, China. <i>Gobiocylindrodon ulausuensis</i> is morphologically more primitive than known later cylindrodontids in having lower-crowned molars, less-rounded upper molars in occlusal view, a more oblique hypolophid on p4, a slightly anterolabially extended hypoconid on m1–3, and a narrow posterosinusid posteriorly and a broad mesosinusid anteriorly on the lower cheek teeth. The lower incisor enamel of <i>G. ulausuensis</i> is pauciserial. Our phylogenetic analysis of a data matrix including 14 taxa and 40 morphological characters reveals that <i>G. ulausuensis</i> is a basal cylindrodontid. <i>Gobiocylindrodon ulausuensis</i> casts new light on early cylindrodontid evolution in Asia and provides new evidence for mammalian dispersals between Asia and North America during the early–middle Eocene. <i>Gobiocylindrodon</i>-bearing strata are probably Arshantan in age.