Résumé
The Oligocene fossil deposits of Ulantatal in Inner Mongolia show an amazing faunal richness, comparable to the highly diversified contemporaneous faunas from the Valley of Lakes in Central Mongolia. To date, only a few taxa have been described. The present study consists of the description of 13 species of cricetid rodents from seven localities ranging in age from the late Early Oligocene to the Late Oligocene epoch. Most of them are new and belong to Eucricetodontinae, the dominating cricetid group at Ulantatal. These taxa give new information regarding the evolution of the Cricetidae in Central and Eastern Asia during the Oligocene. Four new species. Eucricetodon jilantaiensis nov. sp., Eucricetodon bogus nov. sp., Bagacricetodon tongi nov. gen., nov. sp. and Plesiodipus wangae nov. sp., show noticeable evolutionary trends. These species display more derived dental characters than their European contemporaries, in which they are much more comparable to Miocene forms. This observation reinforces the assumed early diversification of cricetids in this part of Asia. A striking case of sympatric evolution is indicated by the similarity of size and dental morphology of two sibling species. Eucricetodon asiaticus and Eucricetodon jilantaiensis nov. sp. Other taxa such as Witenia yolua nov. sp.. Pseudocricetops matthewi nov. gen., nov. sp. and a primitive Tachyoryctoidinae, are scarcely represented and present unusual morphologies. The Cricetidae from Ulantatal also provide evidence suggesting faunal exchanges between Asia and Europe through the Paratethyan pathway during the second half of the Paleogene. (C) 2012 Elsevier Ltd. All rights reserved.