Hyopsodus arshantensis, Bai & Wang & Zhang & Meng, 2021
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publication ID |
https://doi.org/ 10.4202/app.00908.2021 |
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persistent identifier |
https://treatment.plazi.org/id/723787B9-E960-FFD6-FCD6-CF46FF52FCA9 |
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treatment provided by |
Felipe |
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scientific name |
Hyopsodus arshantensis |
| status |
sp. nov. |
Hyopsodus arshantensis sp. nov.
Fig. 1A View Fig .
ZooBank LSID: urn:lsid:zoobank.org:act:79A0AB22-A930-4159-8FB8-BBD321777F76
Etymology: In the reference to the Arshanto Formation, where the new species was found.
Holotype: IVPP V 28282 , a right mandible with m1–m2.
Type locality: Chaganboerhe, Erlian Basin, Inner Mongolia, China.
Type horizon: Upper level of the middle part of the Arshanto Formation (AS-4), Arshantan ALMA, middle Eocene.
Differential diagnosis.—Differs from other species of Hyopsodus by the combination of following characters of m1– m2: a moderate degree of lophodonty, a relatively longer trigonid without a paraconid, a moderately obliquely aligned protolophid, an angle between the cristid obliqua and posthypocristid slightly greater than 90°, a midline position of the hypoconulid on m2, a relatively larger entoconid, and absence of the cingulids on the buccal and lingual sides. Further differs from contemporaneous Bridgerian species of Hyopsodus in having a generally larger size and in lacking a variably developed metastylid. Further differs from H. marshi by a generally less robust appearance. Differs from Asiohyopsodus confuciusi in having more lophodont molar crowns, a more obliquely aligned protolophid, a more lingually directed cristid obliqua, a more distinct posthypocristid and postentocristid, a larger entoconid on m1– m2, and absence of the paraconid on m1.
Material.— Holotype only.
Description.— m1: The tooth is moderately worn and rectangular in outline with the talonid slightly wider than the trigonid ( Table 1). The protoconid and metaconid are conical and obliquely arranged. The protolophid is shallowly notched, joining the posterior walls of the protoconid and metaconid. The paralophid descends from the protoconid anteriorly more than lingually, and then extends lingually to the anterobuccal base of the metaconid. The paraconid is absent, and the trigonid is relatively open and expanded rather than being anteroposteriorly compressed. The hypoconid is as high as the protoconid, extending the cristid obliqua anterolingually to the posterobuccal wall of the metaconid. The posthypocristid, which joins the hypoconid and hypoconulid, is posterolingually extended, and forms an angle of slightly less than 90° with the cristid obliqua at current wear stage. As a result, the hypoconid exhibits a selenodont appearance. The hypoconulid is deeply worn and relatively small, and is positioned closer to the entoconid than to the hypoconid. The entoconid is conical, obliquely arranged relative to the hypoconid, and relatively isolated with a narrow postentocristid joining the hypoconulid. A weak cingulid is present along the anterior border, and the posterior cingulid rises up to form the hypoconulid, with the buccal side of the hypoconulid much more distinct than the lingual one.
m2: The tooth is slightly worn and rectangular in outline with the talonid slightly narrower than the trigonid. The m2 is larger than m1, but is similar to the latter in morphology. The m2 mainly differs from m 1 in that: (i) the buccal wall of the hypoconid is lingually slanted, with the angle between the cristid obliqua and posthypocristid becoming narrower during wear, with the current slightly wear stage associated to an angle slightly greater than 90°; (ii) the hypoconulid is positioned near the midline of the talonid; and (iii) the postentocristid is more distinct, joining the entoconid and hypoconulid.
Stratigraphic and geographic range.— Type locality and horizon only.
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