Comments on the age and dispersal of Microtoscoptini (Rodentia: Cricetidae)

The tribe Microtoscoptini, comprising the genera from Eurasia and and from North America, is an enigmatic group of microtoid cricetids, which was widespread during the Late Miocene. Although fossil remains have been reported from 33 localities, their evolutionary and dispersal history is still poorly understood. Here we give an overview of sites and records and discuss temporal ranges and some aspects of the dispersal history. The branch of cricetids that gave rise to the Microtoscoptini is still unknown. The currently oldest records are those of from Shala in China, considered 8 to 9 Ma and correlated with MN 10 or MN 11. All other remains from Eurasia are distinctly younger (MN 11 – MN 13). The earliest North American records of and are from the early Hemphillian beginning at 9.0 Ma (approximately MN 10 – MN 11 transition). Whether from Shala actually indicates the origin of Microtoscoptini in Asia and subsequent dispersal to North America is still unclear. The presence of Microtoscoptini in both Central Asia and North America during the Late Miocene does suggest dispersal through Beringia. The Microtoscoptini inhabited probably open grasslands locally differentiated by shrubs, tree patches and water bodies. It is far from clear why the Microtoscoptini became extinct even though they had developed an efficient arvicoline-like cheek-tooth pattern.