Eomylus bayanulanensis Meng, Wyss, Hu, Wang, Bowen, and Koch, 2005

Missiaen, Pieter & Smith, Thierry, 2008, The Gashatan (late Paleocene) mammal fauna from Subeng, Inner Mongolia, China, Acta Palaeontologica Polonica 53 (3), pp. 357-378 : 363-364

Eomylus bayanulanensis Meng, Wyss, Hu, Wang, Bowen, and Koch, 2005

Fig. 7 .

Referred material: IMM−2001−SB−027, right m1; IMM−2001−SB−028, right m1; IMM−2001−SB−029, left M2; IMM−2001−SB−030, left m3; IMM−2001−SB−031, left M2; IMM−2001−SB−032, right m2; IMM−2001−SB−033; right DP4; IMM−2004−SB−028, left M1; IMM−2004− SB−029, left P3; IMM−2004−SB−030, right dp4; IMM−2004−SB−031, left P3; IMM−2004−SB−032, right M2.

interpretation, and provide further illustrations of the new specimens of this much discussed taxon.

Stratigraphic and geographic range.— Pseudictops lophiodon is typical for the Gashatan (late Paleocene). P. lophiodon is known from Member I of the Gashato Formation and from the Zhigden and Naran Member of the Naran Bulak Formation ( Mongolia); and from the Nomogen Formation (Inner Mongolia, China).

Description.—Based on comparable size and morphology, and on comparison with related taxa, we were able to identify the previously unknown P3, DP4 and dp4 of Eomylus bayanulanensis . The P3 ( Fig. 7A ) has a simple, ellipsoid shape with two roots and two main cusps of subequal size in unworn specimens. A low ectocingulum with two weak stylar cusps, and a small hypocone can also be distinguished. A similar P3 morphology is known for other basal Glires such as Mimotona , Eurymylus , Heomys , and Sinomylus ( Dashzeveg and Russell 1988; Meng et al. 2003), but the anteroposteriorly short crown, the little expanded hypoconal shelf, and the lingual position of the hypocone are more typical of the upper molars of Eomylus .

IMM−2001−SB−033 is identified as a DP4 ( Fig. 7B ). The general shape of the crown is triangular, and the tooth bears two labial roots and one lingual root. A narrow, bilobed stylar shelf is present, with a large anterior and small posterior stylar cusp. The paracone is small and anteroposteriorly compressed, whereas the metacone is more massive and slightly taller. The preprotocrista forms the anterior border of the tooth and runs toward the anterior stylar cusp. The paraconule is only weakly developed.The postprotocrista is directed toward the metacone and supports a prominent metaconule. The protocone is well developed. The protocone, hypocone and metaconule all exhibit the posterior wear facets also seen in Eomylus zhigdenensis and E. bayanulanensis . The hypocone is small and is slightly more lingually placed than the protocone.

IMM−2004−SB−030 ( Fig. 7E ) is identifiable as the dp4 of E. bayanulanensis . It is similar to the p4 of E. borealis , but differs in having a small, anterior paraconid and a wider, fully developed talonid with a mesoconid and much better developed hypoconid.

Discussion.—The identification of the species of the Gashatan genus Eomylus has been problematic ( Kondrashov and Lopatin 2003), but three species are currently recognized ( Meng et al. 2005). E. borealis and E. bayanulanensis come from two sites in Inner Mongolia, Nomogen and Bayan Ulan respectively, while the type species, E. zhigdenensis , comes from the Mongolian Tsagan Khushu locality. The new specimens from Subeng more closely resemble the teeth of E. bayanulanensis , clearly demonstrating its presence at the Subeng site. The lower molars from Subeng have the marked hypoconid and diagonal wear trough typical of Eomylus ( Meng et al. 2005) , and the partial anterior cingulid and the less transverse crown typical of E. bayanulanensis . The upper molars possess a large hypocone and metaconule, and weak unilateral hypsodonty, features that are characteristic of the upper teeth of E. bayanulanensis ( Meng et al. 2005) .

Stratigraphic and geographic range.— Eomylus bayanulanensis is known from the Gashatan (late Paleocene) Nomogen Formation at Bayan Ulan and Subeng in Inner Mongolia, China.

Figures

Fig. 7. The eurymylid Eomylus bayanulanensis Meng, Wyss, Hu, Wang, Bowen, and Koch, 2005, from the Gashatan (Paleocene) of Subeng, China, in labial (A1–H1), occlusal (A2–H2), and lingual (A3–H3) views. A. IMM−2004−SB−031, LP3. B. IMM−2001−SB−033, RDP4. C. IMM−2004−SB−028, LM1. D. IMM−2001−SB−031, LM2. E. IMM−2004−SB−030, Rdp4. F. IMM−2001−SB−028, Rm1. G. IMM−2001−SB−032, right dentary fragment with m2. H. IMM−2001−SB−030, Lm3. SEM micrographs.