Neimengomys qii, MENG & NI & LI & BEARD & GEBO & WANG & WANG, 2007

MENG, JIN, NI, XIJUN, LI, CHUANKUI, BEARD, K. CHRISTOPHER, GEBO, DANIEL L., WANG, YUANQING & WANG, HONGJIANG, 2007, New Material Of Alagomyidae (Mammalia, Glires) From The Late Paleocene Subeng Locality, Inner Mongolia, American Museum Novitates 3597 (1), pp. 1-32 : 16-21

Neimengomys qii , new spesies

HOLOTYPE: IVPP V14711.1 , a right M1 (or M2) ( fig. 13b ).

INCLUDED SPECIMENS: V 14711.2, left P4; V 14711.3–10, 8 M1s and/or M2s; V 14711.11–14, 4 M3S (or M2s); V 14712.1, right p4; V 14712.2, right m1; V 14712.3–5, 14712.3–5, 3 m3s ( fig. 13 ). See table 5 for measurements.

ETYMOLOGY: The trivial name is after Qi Tao (IVPP), who made the first discovery of Tribosphenomys specimens by screenwashing at Subeng in the 1980s.

DIAGNOSIS: Same as for the genus.

TYPE LOCALITY AND AGE: Subeng, about 25 km west of Erlian, Gashatan, Late Paleocene.

COMPARATIVE DESCRIPTION: A P4 is identified for this species ( fig. 13a ). This tooth is smaller than those of T. minutus and transversely oval-shaped. The P4 buccal shelf is much narrower than that of T. minutus and is similar to that of A. inopinatus ( Dashzeveg, 1990b) . It differs from both Tribosphenomys and Alagomys in bearing a very small cuspule on the buccal shelf.

Nine upper cheek teeth are considered to be either M1 or M2 ( fig. 13b–j ), which we cannot yet distinguish with confidence. These teeth have an oval shape in occlusal view. Compared to M1 of Tribosphenomys minutus these teeth are narrower and less symmetrical along the transverse axis, the protocone is more inflated, the hypocone is more inflated and buccally positioned, and the buccal shelf of the tooth is distinctly narrower. The width/ length ratio of these teeth is similar to that of M2 of T. minutus , but M2 of T. minutus is more triangular in occlusal view, the anterior edge of the tooth is much wider than its posterior counterpart, the protocone is anteroposteriorly more compressed, and the hypocone is usually absent. These teeth are also distinctive in size and morphology from upper molars of T. secundus ( Lopatin and Averianov, 2004a).

The molars of Neimengomys qii differ from M1 and/or M2 of Alagomys in having a hypocone and a more prominent buccal shelf. Among species of Alagomys , N. qii is more comparable with the North American A. russelli than the Asian A. inopinatus and A. oriensis . The Asian species are similar in have an anteroposteriorly compressed protocone, while A. russelli has an inflated protocone and a somewhat oval-shaped occlusal outline ( Dawson and Beard, 1996: plate 1F). Subeng specimens differ from A. russelli in having a distinct buccal shelf on the upper molars, whereas the same structure is completely absent in A. russelli . In addition, the molar cusps of A. russelli are less isolated, the lophs are stronger, the protocone is more inflated, and the trigon basin is deeper. In addition, the basin and postcingulum between the protocone and metaconule are more prominent in Subeng specimens.

Four specimens are identified as M3s ( fig. 13k–n ) of Neimengomys qii because of their small size and reduced metacone. Compared to M3 of T. minutus , the M3 of N. qii is also oval-shaped and has a more inflated, conical protocone. The M3 of N. qii is more transverse and cuspate than those of Alagomys ( Dawson and Beard, 1996; Tong and Dawson, 1995). However, we cannot rule out the possibility that these teeth are M2.

One p4 is identified as N. qii because of its smaller size and unique morphology. Unlike those referred to T. minutus , the p4 ( fig. 13o ) has a narrow trigonid consisting of two closely appressed cusps. In contrast, the talonid is wider than the trigonid and formed by two transverse, ridgelike cuspids. The p4 is similar in morphology to that of T. secundus ( Lopatin and Averianov, 2004a), but differs in being much smaller.

The m1 of N. qii ( fig. 13p ) has a narrower trigonid than those of T. minutus and a hypoconulid that is aligned with the entoconid as a ridge. Three m3s are referred to T. qii ( fig. 13q–s ). The hypoconulid on these m3s is more transverse than conical, differing from those referred to T. minutus . The trigonid basin of the lower molar is somewhat restricted, similar to that of T. minutus . In contrast, the trigonid basin in Alagomys is more open.

Although the material is fragmentary, the morphologies of these teeth show that they must be from a previously unknown taxon. Based on these specimens, we propose a new genus and species of alagomyid.

Figures

Fig. 13. Crown views of cheek teeth of Neimengomys qii from late Paleocene Subeng locality. a. Left P4 (V14711.2). b. Right M2 (or M1, the holotype, V14711.1). c–j. M1s and/or M2 (V14711.3–10). k–n. M3 (or M2s, V14711.11–14). o. Right p4 (V14712.1). p. Right m1 (V14712.2). q–s. m3s (14712.3–5).

Tables

TABLE 5 Tooth Measurements (mm) of Neimengomys qii (Length/Width)

Specimens	L/W	Specimens	L/W
P4 (V14711.2) a	0.45/0.84	M3 (V14711.11) k	0.65/1.22
M1 (V14711.1 b	0.77/1.27	M3 (V14711.13) m	0.63/1.00
M1 (V14711.3) c	0.75/1.31	M3 (V14711.14) n	0.63/1.08
M1 (V14711.4) d	0.81/1.25	p4 (V14712.1) o	0.57/0.53
M1 (V14711.5 e	0.87/1.35	m1 (V14712.2) p	0.96/0.77
M1 (V14711.6) f	0.71/1.21	m3 (V14712.3) q	1.02/0.84
M1 (V14711.7) g	0.79/1.27	m3 (V14712.4) r	1.07/0.81
M1 (V14711.8) h	0.77/1.25	m3 (V14712.5) s	1.02/0.81
M1 (V14711.9) i	0.79/1.25
M1 (V14711.10) j	0.77/1.23