Desmatotherium mongoliense ( Osborn, 1923 )

Bai, Bin, Wang, Yuan-Qing, Mao, Fang-Yuan & Meng, Jin, 2017, New material of Eocene Helaletidae (Perissodactyla, Tapiroidea) from the Irdin Manha Formation of the Erlian Basin, Inner Mongolia, China and comments on Related Localities of the Huheboerhe Area, American Museum Novitates 2017 (3878), pp. 1-44 : 18

Desmatotherium mongoliense ( Osborn, 1923)

Desmatotherium mongoliense Osborn, 1923: 2 .

Desmatotherium mongoliense Matthew and Granger, 1925b: 1 , figs. 1–2.

Helaletes mongoliensis Radinsky, 1965a: 227 , figs. 16–17, pl. 4: figs. 1–4.

Helaletes mongoliensis Reshetov, 1979: 15 , pl. 1: fig. 4.

Irdinolophus mongoliensis Dashzeveg and Hooker, 1997: 113 , figs. 4, 10.

HOLOTYPE: AMNH FM 19161 : Right maxilla with P2–M3.

REFERRED SPECIMENS: AMNH FM 20155: right mandible with p3–m3; AMNH FM 20156: left maxilla with P3–4, right maxilla with M2; AMNH FM 81717: right mandible with p3–m1; AMNH FM 81718: right mandible with p3–4; AMNH FM 81792: right mandible with dp4–m1; AMNH FM 81803: right mandible with p2–m2; PSS.41–3: right M1/2.

NEW MATERIAL: IVPP V 14692 : left maxilla with DP1, P2–M2; IVPP V 23367 , associated upper cheek teeth with right P2–3, left P2–3, M1/2, and M3; IVPP V 23368 , a right mandible with p2–4; IVPP V 23369.1, a right P3; IVPP V 23369.2, a left P4; IVPP V 23369.3, a right M3; IVPP V 23369.4, a right m3 talonid; IVPP V 23369.5–6, two left m3.

LOCALITY AND HORIZON: Irdin Manha escarpment (IVPP V 23368 , V 23369.1–2, 4), Duheminboerhe (IVPP V 23367 ), Huheboerhe (IVPP V 23369.3, 5), and Chaganboerhe (IVPP V 14692 , V 23369.6), Erlian Basin, Inner Mongolia; Irdin Manha Formation, middle Eocene. Mergen, eastern Gobi, Mongolia; Mergen Formation, middle Eocene.

DIAGNOSIS: The ascending process of maxilla with a wide and shallow lateral trough. Infraorbital foramen opening above the posterior end of P4 indicating a short infraorbital canal. Symphysis terminating anterior to p2. P2–4 relatively long and narrow, protocone distally extended with the hypocone rudimentary separated. P2–3 metaloph greatly reduced compared with protoloph. M1–2 metacone concave, short, lingually depressed. The apex of M2 paracone distally curved. M3 metacone highly reduced. p2–4 entoconid large, p4 talonid wider than trigonid. m3 with a rather small hypoconulid.

DIFFERENTIAL DIAGNOSIS: Differs from Desmatotherium intermedius in having P2 hypocone and protocone slightly more separated, P3–4 metaloph extending toward hypocone instead of protocone, M1–3 metacone more lingually depressed, M2–3 centrocrista more aligned with metaloph, M3 more trapezoid in outline, p3–4 talonid not considerably wider than trigonid, and m3 hypoconulid more distinct.