Astigalidae Zhang and Tong, 1981

Missiaen, Pieter & Smith, Thierry, 2008, The Gashatan (late Paleocene) mammal fauna from Subeng, Inner Mongolia, China, Acta Palaeontologica Polonica 53 (3), pp. 357-378 : 360

Family Astigalidae Zhang and Tong, 1981 Astigalidae gen. et sp. indet.

Fig. 2 .

Referred material: IMM−2001−SB−023, left m3; IMM−2004−SB−020, right m3.

Description.—The two referred specimens are similar in having an anteroposteriorly compressed, high trigonid with a nearly connate paraconid and metaconid, and with a weak precingulid. The talonid is much narrower than the trigonid, is strongly elongate and bears a prominent hypoconulid lobe. The lophs connecting different cusps are only weakly developed. The oblique crest is low, and directed toward the lingual part of the base of the protoconid. The entocristid is reduced, leaving the talonid basin open lingually. Although the cusps are high in unworn specimens, the crown is apparently quickly lowered by wear. Both teeth display a limited unilateral hypsodonty. Although there is some difference in the shape of the paraconid between the two specimens, we consider this partly as a difference in wear stage, and partly as intraspecific morphological variability.

Discussion.—The referred specimens possess many characters that have been recognised as diagnostic of “ Anagalida ”: an anteroposteriorly compressed trigonid with partially or completely united paraconid and metaconid, an unreduced m3, and a tendency towards unilateral hypsodonty ( Szalay and McKenna 1971; Tong and Wang 2006). Within the “ Anagalida ”, the Subeng specimens are closest to the enigmatic family Astigalidae , based on a trigonid that is much taller and anteroposteriorly shorter than the talonid, the limited development of lophs, the strong cusps and the lingually open talonid basin. Currently, three different genera of astigalids have been described: Astigale and Zhujegale from the early Paleocene of South China ( Zhang and Tong 1981) and the recently described, more derived Yupingale from the early Eocene of Wutu (Shandong Province, China) ( Tong and Wang 2006). The new Subeng specimens thus partly fill in the temporal gap between both previously described occurrences. Because of their lower crowned, less lophodont morphology, the new late Paleocene specimens from Subeng are morphologically closer to early Paleocene taxa than to the early Eocene Yupingale .

Figures

Fig. 2. The gliriform Astigalidae gen. et sp. indet. from the Gashatan (Paleocene) of Subeng, China, in labial (A1, B1), occlusal (A2, B2), and lingual (A3, B3) views. A. IMM−2001−SB−023, Lm3. B. IMM−2004−SB−020, Rm3. SEM micrographs.