Bumbanius ningi, Missiaen & Smith, 2008

Missiaen, Pieter & Smith, Thierry, 2008, The Gashatan (late Paleocene) mammal fauna from Subeng, Inner Mongolia, China, Acta Palaeontologica Polonica 53 (3), pp. 357-378 : 365-367

Bumbanius ningi sp. nov.

Fig. 9 ; Table 3.

Etymology: In honour of Ning Pei Jie, manager of the Erlian Dinosaur Museum, in Erlianhot (Inner Mongolia, China), who guided and assisted us during fieldwork in the Subeng area since 1995.

Holotype: IMM−2004 −SB−034, right M1?.

Type locality: Subeng, Inner Mongolia, China.

Type horizon: upper part of the Nomogen Formation, Gashatan (late Paleocene).

Referred material: IMM−2001−SB−042, right p4; IMM−2001−SB−043, left m2; IMM−2001−SB−044, right m3; IMM−2001−SB−045, left m1; IMM−2001−SB−046, left m3; IMM−2001−SB−047, left m3; IMM−2001− SB−048, right M1 or M2; IMM−2001−SB−049, fragmentary right M2?; IMM−2001−SB−050, right M1 or M2; IMM−2004−SB−035, right M1 or M2; IMM−2004−SB−036, right M3; IMM−2004−SB−037, right p4; IMM−2004−SB−038, right p4; IMM−2004−SB−039, right m1; IMM−2004−SB−040, left m3; IMM−2004−SB−041, right m2; IMM−2004−SB−042, right m2; IMM−2004−SB−043, left M1?; IMM−2004−SB−044, right p4.

Diagnosis.—Praolestine nyctitheriid similar in size to Bumbanius rarus . Differs from B. rarus by the taller trigonid on lower molars, the more pronounced hypoconulid on m3 and the more transversely expanded upper molars. Differs from Praolestes by the lower position of the paraconid on p4 and by the less transversely expanded upper molars with strong conules and conule crests. Differs from all other Praolestinae by the expanded talon shelf with large hypocone.

Description.—The upper molars ( Fig. 9A, B ) have a transversely expanded crown with generally well−developed cusps and crests. The stylar shelf is narrow and lacks cusps. The paracone and metacone are equally robust, closely spaced and slightly fused at the base. The paraconule and metaconule are both well developed, with the paraconule slightly the more robust. The conule wings and pre− and postprotocrista all are clearly present on the upper molars. The protocone is about the same height as the paracone and metacone, but is the most massive molar cusp. A narrow precingulum is present, as well as a relatively wide postcingulum with a rounded posterior border and a prominent hypocone. Because the M1 and M2 of Praolestinae have a similar structure ( Lopatin 2006), and the upper molars available to us are all isolated and similar in form, it is difficult to differentiate M1 and M2 with certainty, although the holotype specimen probably represents an M1 based on the anteriorly directed parastyle and the shallow ectoflexus.

The M3 ( Fig. 9C ) is moderately smaller than the preceding molars, with a reduced stylar shelf and lower paracone and metacone The conules and associated crests are reduced, the precingulum is absent and the postcingulum is much smaller with only a faint trace of a hypocone.

None of the referred p4s is complete, but the available specimens ( Fig. 9D–F ) suggest that p4 is relatively large and semimolariform. The paraconid projects anteriorly and bears a small precingulid. The protoconid is the main trigonid cusp, with the smaller metaconid closely appressed to it and somewhat more posterior in position. The talonid is simple, consisting only of a single talonid cusp.

The m1 ( Fig. 9G ) has a moderately tall trigonid in which the metaconid is slightly more robust and higher than the protoconid. The paraconid arises from high on the metaconid and slightly labial to it, and is connected to the protoconid by a strong paracristid. The anterior side of the paracristid bears a moderate precingulid. The oblique crest connects the hypoconid to the middle of the trigonid wall, but does not rise high onto it. All three talonid cusps are subequal in height but the hypoconid is the most robust. The apex of the entoconid is displaced slightly posterolabially toward the hypoconulid, forming a more rounded posterolingual edge to the talonid. In contrast, the labially protruding hypoconid forms a more acute angle.

The m2 ( Fig. 9H ) is the largest lower molar, with a more anteroposteriorly compressed trigonid than m1. The m3 ( Fig. 9I ) is narrower than m2 and only slightly longer; it supports a small hypoconulid lobe, and the crests running from the hypoconid and entoconid toward the hypoconulid variably curve toward one another and fuse before reaching the hypoconulid. Discussion.— Bumbanius ningi sp. nov. described here strongly resembles the type species Bumbanius rarus from the early Eocene of Mongolia in having well−developed cusps and crests on the upper molars, a narrow labial cingulum, and in the presence of both a pre− and postcingulum. The lower cheek teeth of B. ningi resemble those of B. rarus in the precingulid, the large metaconid, the strong hypoconid and the U−shaped notch in the entocristid. B. ningi differs from B. rarus , however, in having more transversely elongated upper molars and a better−developed postcingulum and hypocone, in the slightly taller molar trigonids, with a higher positioned paraconid, and in the stronger hypoconulid lobe on m3 ( Russell and Dashzeveg 1986).

The genera Bumbanius and Praolestes have been grouped in the subfamily Praolestinae ( Lopatin 2006) . B. ningi resembles Praolestes in the semimolariform p4, in the anteroposteriorly short molar trigonids that are dominated by the high, large protoconid and metaconid, and in the shape of the postcristid on m3. Important features distinguishing B. ningi from Praolestes are the strong conules and the large talon and hypocone on the upper molars, and the large p4. Because of the clear and discrete nature of the latter differences, we assign our new specimens to a new species of Bumbanius rather than a new species of Praolestes . However, B. ningi is a morphological intermediate between B. rarus and Praolestes , considering the transverse length of the upper molars, the position of the paraconid on p4, the height of the lower molar trigonid and the expression of the hypoconulid lobe on m3. The discovery of such an intermediate form is an additional reason for grouping the two genera together and we suggest that B. ningi is more primitive predecessor to the Eocene B. rarus .

Figures

Fig. 9. The nyctitheriid Bumbanius ningi sp. nov., from the Gashatan (Paleocene) of Subeng, China, in labial (A1–I1), occlusal (A2–I2), and lingual (A3–I3) views. A. IMM−2004−SB−035, RM1 or M2. B. IMM−2004−SB−034 (holotype), RM1?. C. IMM−2004−SB−036, RM3. D. IMM−2004−SB−037, Rp4. E. IMM− 2004−SB−038, Rp4. F. IMM−2001−SB−042, Rp4.G. IMM−2004−SB−039, Rm1. H. IMM−2001−SB−043, Lm2. I. IMM−2001−SB−044, Rm3. SEM micrographs.