Two New Mylagaulid Rodents from the Early Miocene of China

<div><p>Mylagaulid fossorial rodents are a common component of North American Miocene fossil faunas. However outside of North America, only three species are known from Asia. Here we report two new mylagaulids, <i>Irtyshogaulus minor</i> gen. et sp. nov. and <i>Irtyshogaulus major</i> gen. et sp. nov., recovered from early Miocene sediments in the Junggar Basin in northwestern China. The two new taxa are small-sized, high-crowned promylagauline rodents. Their lower molars possess high metastylid crests, small mesostylids, broad and posterolingually expanded labial inflections, and transversely extending metalophid IIs. The mesoconid is absent in both species. The anterior and posterior fossettids are large and equally developed. Their upper M1-2s possess a square occlusal surface with five deep fossettes. The two new taxa are distinguished from each other mainly by their size, the morphology of fossettes and fossettids, development of mesial and distal lophs, posterior reduction of M3, and the orientation of m2 hypolophid. Our phylogenetic analysis indicates that <i>Irtyshogaulus</i> and <i>Lamugaulus</i> (another early Miocene Asian mylagaulid) are sister taxa. The two genera are nested among the North American promylagaulines, and share a common ancestor from North America, indicating early Miocene intercontinental dispersal within this clade of rodents.</p></div

Measurements for <i>Irtyshogaulus minor</i> gen. et sp. nov.

<p>Measurements for <i>Irtyshogaulus minor</i> gen. et sp. nov.</p

Terminology used for the mylagaulid molars.

<p>(A), Upper molar; (B), Lower molar.</p

Phylogeny and distribution of mylagaulid and aplodontine rodents.

<p>Strict consensus is from 58 most-parsimonious trees. Each tree has a Best Score of 1585, a Consistency Index of 0.1684 and a Retention Index of 0.6659. (A), Summarized phylogeny of Aplodontoidea, showing the phylogenetic positions of Mylagaulidae and Aplodontinae; (B), Phylogeny of Mylagaulidae and Aplodontinae. Branch lengths indicate the number of character changes, but have no temporal meaning. The paleobiogeographic distribution of mylagaulids and aplodontines was reconstructed by using parsimony criterion in Mesquite v3.03: black for North America, red for Asia, and blue for equal parsimony. Dashed square brackets on the right show the previously published classifications, and solid line brackets show the classification scheme used in this paper.</p

Upper and lower teeth of <i>Irtyshogaulus minor</i> gen. et sp. nov.

<p>(A), V 20328, left M1 (holotype); (B), V 20329.1, left M1; (C)-(E), V 20329.2–4, right M1s; (F), V 20329.5, left M2; (G)-(H), V 20329.6–7, right M2s; (I), V 20329.8, left M3; (J)-(L), V 20329.9–11, right M3s; (M)-(N), V 20329.12–13, right m1s; (O), V 20329.14, left m2; (P), V 20329.15, right m2; Scale bar, 1 mm.</p

Two new Pliocene hamsters (Cricetidae, Rodentia) from southwestern Tibet (China), and their implications for rodent dispersal ‘into Tibet’

<p>Two new species of fossil hamsters (Cricetinae, Cricetidae) collected from early Pliocene sediments (∼4.4 Ma) in the Zanda Basin, southwestern Tibet (China), demonstrate greater past diversity among cricetines in the hinterland of the Tibetan Plateau within the Himalayan Range (beyond the previously known ‘<i>Plesiodipus</i>’ <i>thibetensis</i> from the late Miocene of the Gyirong Basin). The occurrence of <i>Nannocricetus qiui</i>, sp. nov., in the Zanda Basin indicates a dispersal of <i>Nannocricetus</i> from its center of origin in northern and northwestern China and the Mongolian Plateau, into the hinterland of the high-elevation Tibetan Plateau and subsequently into the Himalayan Range. The new taxon <i>Aepyocricetus liuae</i>, gen. et sp. nov., possibly represents a specialized (and endemic) Neogene hamster from the Tibetan Plateau. The dispersal of these hamsters into the high-elevation portions of Tibet during the early Pliocene contrasts with the hypothesized biogeographic shift of several large mammal lineages out of Tibet. The absence of <i>Aepyocricetus</i> and <i>Nannocricetus</i> from adjacent portions of the south slope of the Himalayans (and the Siwalik Hills in India and Pakistan) further implies that the Himalayan range functioned as a dispersal barrier for these small mammals by the early Pliocene.</p> <p>http://zoobank.org/urn:lsid:zoobank.org:pub:9EE286AA-0C00-4041-8F0C-877B35283181.</p> <p>SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at <a href="http://www.tandfonline.com/UJVP" target="_blank">www.tandfonline.com/UJVP</a></p> <p>Citation for this article: Li, Q., T. A. Stidham, X. Ni, and L. Li. 2018. Two new Pliocene hamsters (Cricetidae, Rodentia) from southwestern Tibet (China), and their implications for rodent dispersal ‘into Tibet’. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1403443.</p