Phylogenetics PG_W0005

Title : An Early Miocene microtoid cricetid (Rodentia, Mammalia) from the Junggar Basin of Xinjiang, China
Author : OLIVIER MARIDET, WENYU WU, JIE YE, JIN MENG, SHUNDONG BI, AND XIJUN
NI
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Abstract :

 Microtoid cricetids are widely considered to be the ancestral form of arvicoline rodents, a
successful rodent group including voles, lemmings and muskrats. The earliest previously
known microtoid cricetid is Microtocricetus molassicus Fahlbusch and Mayr 1975 from the
MN9 (about 10-11 Ma) of Europe. Here we report a new microtoid cricetid, Primoprismus
fejfari, gen. et sp. nov., discovered from locality XJ 200604 in the Junggar basin of Xinjiang,
northwest China. The rodent assemblage found in association with this specimen indicates a
late Early Miocene age, roughly estimated at 18–17 Ma, and thus more than 6 million years
earlier than the record of M. molassicus. While morphological comparisons suggest that the
new taxon is most closely related to M. molassicus, it also presents a striking combination of
primitive characters compared to the latter, including its relatively lower crown, smaller size,
differentiated posterolophid and hypolophid, faint anterolophid, and the absence of an
ectolophid, as well as the presence of a stylid on the labial border of the tooth. Arid conditions
prevailing across the mid-latitude interior of Eurasia during the Early Miocene, enhanced by
the combined effects of the Tibetan uplift and the gradual retreat of the Tethys Ocean, likely
played a role in the appearance of grasslands which triggered the evolution of microtoid
cricetids and, ultimately, the origin of arvicoline rodents.