Yuomys sp.

Li, Qian, Wang, Yuan-Qing & Fostowicz-Frelik, Łucja, 2016, Small mammal fauna from Wulanhuxiu (Nei Mongol, China) implies the Irdinmanhan-Sharamurunian (Eocene) faunal turnover, Acta Palaeontologica Polonica 61 (4), pp. 759-776 : 773

Yuomys sp.

Fig. 14 .

Material.—Fragmentary right maxilla with M1 (V20829.1), fragmentary right mandible with m2–m3 (V20829.2) from Wulanhuxiu, Erlian Basin, Nei Mongol, China, upper part of horizon 4, middle Eocene.

Description.—The M1 (length 3.00 mm, width 3.50 mm; Fig. 14A ) has a well-developed hypocone and metaloph directed toward but never in contact with the protocone. On M1 there is no paraconule, but the metaconule is distinct, being larger than the metacone. On m2–m3 (m2, length 2.90 mm, width 2.50 mm; m3, length 3.70 mm, width 2.80 mm; Fig. 14B ) the postprotocristid is short, the trigonid basin is open posteriorly, and the transverse hypolophid extends to the complete ectolophid. All these features are similar to those of Yuomys .

Compared to Yuomys cavioides ( Li, 1975) , the new specimens from Wulanhuxiu are smaller, have a weaker postprotocristid, and lack a conule on the hypolophid on m2–m3. The new specimens differ from Y. eleganes ( Wang, 1978) in being smaller, and having a short anterior cingulum on M1 and with the metaconid located no farther anteriorly than the protoconid on m2–m3. Differences from Y. weijingensis ( Ye, 1983) include weaker parastyle and metaloph on M1, and lack of mesostylid and conule on the hypolophid. Y. yunnanensis ( Huang and Zhang, 1990) differs from the new specimens in larger size, and longer postprotocristid that contacts the base of the metaconid on m2. Differences from Y. huangzhuangensis ( Shi, 1989) are: smaller size and smaller ratio of length to width of M1 (length/width 0.86 in new specimens, 1.07 in Y. huangzhuangensis ).

In general, the new specimens have morphologically simpler teeth that lack a mesoconid on m2–m3, a mesostylid and a conule on the hypolophid. Among all the known species, the new specimens are most similar to Y. huheboerhensis from the Irdin Manha Formation of the Huheboerhe section, Erlian Basin ( Li and Meng 2015) morphologically, but Y. huheboerhensis is smaller than the new specimens, and its M1 and M2 are both approximately as long as wide in occlusal view, and sometimes m3 has an ectomesolophid.

Figures

Fig. 14. Ctenodactyloid rodent Yuomys sp. from the Eocene of Wulanhuxiu, Nei Mongol, China. A. Right maxilla with M1 (IVPP V20829.1). B. Right mandible with m2–m3 (IVPP V20829.2). All in occlusal view.