Bienotheroides shartegensis, Watabe & Tsubamoto & Tsogtbaatar, 2007

Watabe, Mahito, Tsubamoto, Takehisa & Tsogtbaatar, Khishigjav, 2007, A new tritylodontid synapsid from Mongolia, Acta Palaeontologica Polonica 52 (2), pp. 263-274 : 264-265

Bienotheroides shartegensis sp. nov.

Figs. 3–6 , 7C .

Holotype and only known specimen: MPC−Nd 10 /301, an incomplete skull associated with right and left lower jaws. Casts of MPC−Nd 10 /301 are deposited in HMNS ( HMNS 1486 and 1491).

Type locality: Ulaan Malgait Hills, Shar Teg locality, Gobi−Altai Aimag, southwestern Mongolia ( Fig. 2 ; Gubin and Sinitza 1996).

Formation and age: From a red mudstone bed of the lower part of the Ulaan Malgait Beds (about 10 meters above the boundary between the Ulaan Malgait Beds and the underlying Shar Teg Beds); Upper Jurassic ( Gubin and Sinitza 1996).

Derivation of the name: Named after the type locality.

Diagnosis.—Differs from the other species of Bienotheroides in having a much smaller M1 cusp. Differs from Bienotheroides zigongensis and Bienotheroides ultimus in

having proportionally shorter and wider PC/pc. Differs from B. ultimus in lacking a projection on the middle part of the mesial margin of PC. Differs from Bienotheroides wansienensis in lacking B0 cusp and a diastema between upper I1 and I2.

Figures

Fig. 3. Tritylodontid Bienotheroides shartegensis sp. nov., MPC−Nd 10/301, Upper Jurassic; Shar Teg, Mongolia. A. Ventral view of the skull with the posterior part of the right lower jaw; A1, stereo−photograph; A2, schematic drawing. B. Dorsal view of the skull with the posterior part of the right lower jaw; B1, stereo−photograph; B2, schematic drawing.

Fig. 4. Tritylodontid Bienotheroides shartegensis sp. nov., MPC−Nd 10/301, Upper Jurassic; Shar Teg, Mongolia. A. Left lateral view of the skull with the posterior part of the right lower jaw; A1, stereo−photograph; A2, schematic drawing. B. Right lateral view of the skull right and left lower jaws; B1, stereo−photograph; B2, schematic drawing.

Fig. 5. Tritylodontid Bienotheroides shartegensis sp. nov., MPC−Nd 10/301, Upper Jurassic; Shar Teg, Mongolia. A. Dorsal view of the left and anterior part of right lower jaw; A1, stereo−photograph; A2, schematic drawing. B. Left lateral view of the left lower jaw; B1, stereo−photograph; B2, schematic drawing. C. Lingual view of the right upper and lower postcanine teeth in occlusion; C1, stereo−photograph; C2, schematic drawing. D. Buccal view of the right upper and lower postcanine teeth in occlusion; D1 stereo−photograph; D2, schematic drawing. Upper scale corresponds to A and B; and lower scale corresponds to C and D.

Fig. 6. Tritylodontid Bienotheroides shartegensis sp. nov., MPC−Nd 10/301, Upper Jurassic; Shar Teg, Mongolia. A. Occlusal view of the left upper postcanine dentition; A1, stereo−photograph of an epoxy cast; A2, schematic drawing. B. Occlusal view of the left lower postcanine dentition; B1, stereo−photograph of an epoxy cast; B2, schematic drawing.

Fig. 7. Comparison of right upper postcanine teeth among the species of Bienotheroides in occlusal view (not to scale). A. Bienotheroides wansienensis (after Sun 1984b). B. Bienotheroides zigongensis (after Sun 1986). C. Bienotheroides shartegensis sp. nov. (reversed). D. Bienotheroides ultimus (after Maisch et al. 2004).

Fig. 2. Map of Mongolia, showing the Shar Teg locality (star) of Gobi Altai Aimag (gray area). The Shar Teg locality, dated as the Upper Jurassic, has yielded the type specimen of Bienotheroides shartegensis sp. nov.