Erenlagus anielae Fostowicz-Frelik and Li, 2014

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 : 765-766

Erenlagus anielae Fostowicz-Frelik and Li, 2014

Figs. 5 , 6 .

Material.—left M1 (IVPP V20260), right m2(IVPP V20258) from Wulanhuxiu, Erlian Basin, Nei Mongol, China, horizon 4, Irdinmanhan (middle Eocene).

Description.—The M1 matches in size that of the type sample (the crown width is 2.37 mm and the crown length 1.47 mm; see Fostowicz-Frelik and Li 2014). The upper molar is worn and the buccal roots are broken ( Fig. 5 ). The occlusal surface is symmetrical and roughly rectangular, which indicates M1 rather than M2. The remains of an almost vanished crescent are asymmetrical (with the anterior arm larger) and shifted anteriorly. There is a narrow and small hypostrial lake positioned diagonally, separating the trigon from the hypoconal shelf. The hypostria is only a shallow indentation. The protocone is slightly larger than the hypocone, and it protrudes farther lingually then the latter. The hypoconal shelf is not inflated, covering roughly 30% of the occlusal surface, it is relatively extended buccolingually but short anteroposteriorly. The tooth curvature is slightly greater than in the upper molars of Erenlagus from Huheboerhe.

The m2 is close (apart from the more strongly bent roots) to the holotype specimen ( Fig. 6 ; see also Fostowicz-Frelik and Li 2014: fig. 2A–J). The occlusal surfaces of the trigonid and talonid are lingually confluent as in the holotype. The length of the occlusal surface is 1.65 mm and the maximum crown height equals 1.98 mm; the trigonid (1.88 mm in width) is oval with flattened anterior and posterior edges. The metaconid is higher than the protoconid, even at this strongly worn stage, and both cusps are aligned. The enamel layer surrounding the protocone is thickened markedly. The anterior wall of the trigonid is concave and displays a wide enamel-less hiatus. The occlusal surface of the talonid (1.41 mm in width) is placed lower than the trigonid one; it is generally rectangular with a tapering buccal side. The entoconid is placed more distally than the hypoconid, but both have a similar height. The poorly distinguished hypoconulid is aligned with the entoconid and both cusps form a straight flat distal margin of the talonid. The anterior margin of the talonid is irregular curving anteriorly. The whole tooth column is slightly bent distally, which is typical of m 2 in lagomorphs. The roots are broken apically. The part which is preserved shows a fused condition, with the apical trigonid and talonid part distinct, but having a common root chamber. In this respect the Wulanhuxiu specimen is different from the type specimen, in which the roots have separate dental chambers.

Stratigraphic and geographic range.—Irdin Manha Formation and Ulan Shireh Formation, Irdinmanhan, middle Eocene, Erlian Basin, Nei Mongol, China.

Figures

Fig. 5. Lagomorph Erenlagus anielae Fostowicz-Frelik and Li, 2014 from the Eocene of Wulanhuxiu, Nei Mongol, China. Left M1 (IVPP V20260) in occlusal (A) and posterior (B) views.

Fig. 6. Lagomorph Erenlagus anielae Fostowicz-Frelik and Li, 2014 from the Eocene of Wulanhuxiu, Nei Mongol, China. Right m2 (IVPP V20258) in occlusal (A), apical (B), mesial (C), lingual (D), distal (E), and buccal F) views.