Lambdopsalidae Chow and Qi, 1978

Mao, Fang-Yuan, Wang, Yuan-Qing & Meng, Jin, 2016, New specimens of the multituberculate mammal Sphenopsalis from China: Implications for phylogeny and biology of taeniolabidoids, Acta Palaeontologica Polonica 61 (2), pp. 429-454 : 433

Family Lambdopsalidae Chow and Qi, 1978

Type genus: Lambdopsalis Chow and Qi, 1978 .

Included genera: Sphenopsalis Matthew, Granger, and Simpson, 1928 .

Emended diagnosis.—Differ from other multituberculates, including the North American taeniolabidoids, in having a combination of the following features: tooth formula 2.0.1.2/1.0.1.2; upper incisors anteriorly positioned, simple and pointed, with circular cross-section, and lacking diastema between I2 and I3; long diastema between I3 and P4; M1 cusp formula 7:7:8, M2 cusp formula 1:2:4; occlusal surface of molars, particularly M2/m2 forming a sloped trench with a broad V-shape in distal view; M2 cusps crescentic, with the two medial cusps in the shape of an oblique, strong ridge and nearly twice the width of the lingual ones; lower incisor with circular cross-section; m1–2 cusp formula 5:4 and 3:2, respectively; m1 significantly narrower than m2, with distal end wedged in the notched mesial surface of m2; the two lingual cusps of m2 strongly crescentic and about twice the width of the buccal cusps.

Geographic and stratigraphic range.—Upper Paleocene (Gashatan) of Mongolia and China.