Neocometes sp.

Qiu, Zhuding & Ni, Xijun, 2019, Platacanthomyids (Rodentia, Mammalia) From The Late Miocene Yuanmou Hominoid Locality Of Yunnan, China, Fossil Imprint 75 (3 - 4), pp. 383-396 : 384-385

Neocometes sp.

Text-fig. 2

R e f e r r e d m a t e r i a l. One right M 3 and one left M 2 (IVPP V 25882.1–2) from Loc. 9905, Leilao, Yuanmou.

M e a s u r e m e n t s. M 3: 1.65 × 1.40 mm; M 2: 2.05 ×

1.55 mm (length × width).

D e s c r i p t i o n. The M 3 is subrectangular in occlusal view, with longitudinally concave grinding surface. It is unilaterally hypsodont, with the lingual crown height distinctly higher than the buccal one. The anteroloph is connected with the endoloph lingually and separated from the paracone by a notch buccally. The anterior extra ridge is fused with the anteroloph to form a thick lingual portion of the ridge. The protoloph is pronounced, but distinctly constricted at the contact with protocone. Its mesial angle to the longitudinal axis is about 70°. The buccally free mesoloph is almost as thick as, and roughly parallel to the protoloph. The metaloph is interrupted into two cusp-like parts, with the lingual one connecting with the hypocone and the posteroloph, and the buccal one with the mesoloph and the metacone. The posteroloph is thin and curved backwards, originating from the hypocone and extending to the base of metacone. The endoloph is continuous, but indicative of a weaker connection between the protocone and hypocone in early stages of wear. Syncline Ia is absent. Syncline I is narrow and shallow, lingually closed and buccally opened. Syncline II is the longest syncline of the tooth, widely opened buccally. The buccally open syncline III and the distinct syncline IV are interrupted by the incomplete metaloph. The M 3 has two smaller anterior roots and a larger posterior one.

The M 2 is longer than wide and rectangular in occlusal view, with straight anterior margin, curved posterior margin and nearly parallel lateral margins. The grinding surface is longitudinally concave, consisting of five thick diagonal/ transversal ridges and four synclines. The anterolophid is nearly transverse, extending from the paraconid to the anterolingual corner of the tooth. The anterior extra ridge is completely confluent with the anterolophid to thicken the lingual portion of the ridge. The paraconid-metaconid connection is thick and slightly curved posterobuccally. The laterally free mesolophid is as strong as, and roughly parallel to the paraconid-metaconid connection, with a ~70° mesial angle to the longitudinal axis. The lingually free hypolophid is oriented nearly transversely, and slightly constricted at the contact with the hypoconid buccally. The posteriorly curved posterolophid is also prominent, extending from the hypoconid to the posterolingual corner of the tooth. The endolophid is not continuous. Syncline Ia is obliterated. Syncline I is a closed furrow obliquely situated. Syncline II and syncline III are longer, laterally opened, and similar in orientation. The lingually opened syncline IV is like syncline I in length, but more transversely directed. The M 2 has two roots.

D i s c u s s i o n. The two teeth exhibit characters that are highly diagnostic for the genus Neocometes SCHAUB et ZAPFE, 1953 : the concave grinding surface, the distinctly inclined mid-ridges/synclines, the opening of the midbuccal synclines on M 3, and the laterally open synclines II and III on M 2. By these features, they can be easily distinguished from Platacanthomys and Typhlomys in the family Platacanthomyidae . Moreover, the two teeth show consistency in: the relatively large size with strong and crowded ridges, the fused anterior extra ridge with the anteroloph(id), and the early obliteration of syncline Ia.

Neocometes similis , Neocometes cf. N. similis and N. brunonis from Europe, and five species from Asia, N. orientalis , Neocometes cf. N. orientalis ( Thailand) , N. sinensis , N. magna ( China) and Neocometes aff. N. similis ( South Korea) are documented in the early or middle Miocene ( Schaub and Zapfe 1953, Fahlbusch 1966, Fejfar 1974, 1999, Mein et al. 1990, Mein and Ginsburg 1997, Fejfar and Kalthoff 1999, Chaimanee et al. 2007, Lee and Jacobs 2010, Qiu and Jin 2017). Remains of these taxa are usually scarce, especially those from Asia. This scarcity hinders attempts to effectively compare the two teeth from Yuanmou with other species, because corresponding teeth, either M 3 or M 2 are absent in most samples from Asia. As far as dimension is concerned, the two teeth are larger than those of any previously described sample other than N. magna . In addition, the Yuanmou specimens are characterized by their strong and crowded ridges, and confluence of anterior extra ridge with the anteroloph(id). By these characters they can be distinguished from most other known taxa. The M 2 differs from the corresponding tooth of N. orientalis and N. cf. N. orientalis in having a lingually opened syncline III. There is a possibility that the specimens described may be referred to N. sinensis , because of the closeness in size and the presence of similar ridges, but no corresponding teeth are available for comparison. The scarcity of the material renders it impossible to give a more definitive identification below the generic rank.

The indeterminate species represented by the two teeth from the late Miocene deposits of Yuanmou is considered the latest occurrence of the genus. Its dental characters and late occurrence deserve further attention. Whether it can be assigned to a new species of Neocometes must await more material.

Figures

Text-fig. 2. Neocometes sp. from Leilao, Yuanmou. a) right M3 (IVPP V 25882.1, reversed), b) left M (IVPP V 25882.2). 2