Chalicotheriinae Gill, 1872

Chavasseau, Olivier, Chaimanee, Yaowalak, Coster, Pauline, Emonet, Edouard-Georges, Soe, Aung Naing, Kyaw, Aung Aung, Maung, Aye, Rugbumrung, Mana, Shwe, Hla & Jaeger, Jean-Jacques, 2010, First record of a chalicothere from the Miocene of Myanmar, Acta Palaeontologica Polonica 55 (1), pp. 13-22 : 15-16

Subfamily Chalicotheriinae Gill, 1872

Gen. et sp. indet.

Figs. 4 , 5 .

Locality and age: MFI−105 was discovered in early late Miocene Khoratpithecus −bearing outcrops at N20°06'30.56'' E95°07'28.25'', near the village of Ondwe which is situated 20 km southeast of Magway ( Fig. 1 ) .

Material.—MFI−105, left hemimandible corpus belonging to an adult individual and preserving a long portion of the diastema, the root of the p2, p3–m1 crowns and the partial anterior alveolus of the m2. This fossil is conserved at the Department of Archaeology of the National Museum and Library of Mandalay under the authority of the Ministry of Culture of the Union of Myanmar.

Description.—MFI− 105 specimen preserves the central portion of the corpus, which is slender and straight. The anterior doi:10.4202/app.2009.0033

tooth and joins the summit of the protoconid. There is no distinct paraconid at the origin of this paralophid. A short and mostly mesio−distally oriented protolophid starts from the apex of the protoconid and descends linguo−distally, but there is no distinct metaconid. The talonid, whose lingual wall is damaged, is as long as the trigonid. It displays a disto−buccally directed metalophid, which is connected mesially to the protolophid and distally to the hypoconid. The orientation of the metalophid shows only a weak buccolingual component. The height of the hypoconid is approximately half that of the protoconid. Buccally, a weakly expressed valley closed by a low cingulum separates the protoconid from the hypoconid. The features of the disto−lingual part of the tooth (e.g., possible presence of an entoconid) are not accessible because of damage.

The p4, displaying a paraconid, a metaconid and an entoconid, is more molarized than the p3. Its outline is subrectangular with a trigonid equal in length to the talonid but distinctly narrower than the latter ( Table 1). The stage of wear of this tooth is faintly more advanced than that of the p3. The crest patterns are similar to those of the p3, except that they possess more oblique orientations. The mesio−lingual valley is U−shaped. Its opening is wide because the paralophid does not extend to the lingual half of the crown. Contrary to the condition displayed by the p3, the hypoconid is nearly as high as the protoconid. The buccal valley is deeper and wider than on the p3 but remains closed by a low cingulum. A distinct entoconid is discernible disto−lingually. This cusp is bucco−lingually elongated, lower and less worn than the other cusps, and connected to the hypoconid by a weak hypolophid.

The m1 is strongly worn and exhibits an outline close to that of the p4, except for a greater length ( Table 1). The trigonid is shorter than the talonid. The paralophid is more transverse and more lingually extended than those of the premolars. Combined with the advanced stage of wear, this renders the anterior lingual valley narrow and U−shaped in occlusal view. The region of the metaconid is too worn to determine whether a “metastylid” was present or not. The appearance of the wear outline indicates that this tooth most probably possessed a fully developed entoconid and a hypolophid. As observed on the p3 and the p4, a thin cingulum closes the opening of the buccal valley. A weak and low cingulum is also present at the opening of the posterior lingual valley while a thicker cingulum surrounds the posterior wall.

Figures

Fig. 4. Chalicotheriine mandible MFI−105 from the early late Miocene of Ondwe (Magway province, Myanmar) in occlusal view (A), enlarged occlusal view of the teeth (B), buccal view (C), and lingual view (D).

Fig. 5. Interpretive drawings of MFI−105 from the early late Miocene of Ondwe (Magway province, Myanmar) in buccal (A) and lingual (B) views.

Fig. 1. A. Map of Myanmar showing the area of study within the Myanmar Central Basin. B. Detailed map of the Magway region positioning the outcrops that yielded the chalicothere mandible MFI−105.