Gobiomys exiguus Wang, 2001
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publication ID |
https://doi.org/ 10.4202/app.00292.2016 |
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persistent identifier |
https://treatment.plazi.org/id/03E687D4-FFFC-FFC6-FFE9-794BFE8821E4 |
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treatment provided by |
Felipe |
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scientific name |
Gobiomys exiguus Wang, 2001 |
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Fig. 13 View Fig .
Material.—Right M2 (V20827.1), right M3 (V20827.2), left lower jaw with m1 (V20827.3), right m2 (V20827.4) from Wulanhuxiu, Erlian Basin, Nei Mongol, China, upper and middle part of horizon 2, middle Eocene.
Description.—The M2 is square (length 1.50 mm, width 1.50 mm) in crown outline ( Fig. 13A View Fig ). The protocone, paracone, and metacone are all well-developed. A distinct hypocone is present but smaller than the protocone. The metaconule is subequal and anterolingual to the metacone. The protoloph is complete and the protoconule is absent. A weak metaloph extends from the metacone to the metaconule, whereas the metaconule and protocone are isolated from one another. The anterior cingulum is well developed and reaches the protoloph lingually. The entoloph is absent.
M3 (length 1.60 mm, width 1.50 mm) has a rounded triangular outline in occlusal view ( Fig. 13B View Fig ). The metacone is reduced, and the hypocone is slightly buccally displaced and smaller than that of M2. The metaconule is absent and the well-developed metaloph extends to the protocone. The anterior and posterior cingula are distinct.
The m1 (length 1.30 mm, width 1.20 mm) is oval in occlusal view, with wider posterior side ( Fig. 13C View Fig ). The m2 (length 1.80 mm, width 1.60 mm) is larger than m1 ( Fig. 13D View Fig ). The protoconid and metaconid of m1 and m2 are prominent and connected by a low but complete preprotocristid. The protoconid and hypoconid are larger than the two lingual cuspids. The postprotocristid is short and extends rather posteriorly. In m1 and m2 a distinct hypoconulid is situated at the mid-point of the posterior margin of the talonid. The hypolophid of m1 and m2 is absent. The ectolophid is complete and located buccally with respect to the middle longitudinal line.
Gobiomys was described by Wang (2001), and includes three species, G. neimongolensis , G. exiguus , and G. asiaticus . The new specimen differs from G. neimongolensis in being smaller, in having a weaker metaloph on M2, and a more buccally located ectolophid on m1. In G. asiaticus the lower molars have a complete arm of the entoconid reaching to the hypoconid, but in the new specimens the hypolophid of m1–m2 is absent. Moreover, G. asiaticus differs from the new specimen in having wider and shorter upper molars. The new specimen shares the following features with G. exiguus : small size, absence of protoconule, distinct metaconule and short metaloph on M2, and the absence of the lingual part of the postprotocristid and of entoconid arm on the lower molars. Compared to the holotype of G. exiguus , the specimens reported here are slightly larger.
Stratigraphic and geographic range.—Middle Eocene, Nei Mongol, China.
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