New fossil mammal materials found in the upper Lingcha Formation of the Hengyang Basin, Hunan, China, include a complete skull of Hapalodectes hetangensis and a taxon new to the fauna, Dissacus zengi, n. sp. H. hetangensis is the morphologically least derived species of the genus and currently is the earliest known record of the genus. D. zengi, n. sp. is the second Asian early Eocene record of the genus and represents the last occurrence of the genus in Asia.

The Lingcha Formation includes two fossiliferous intervals. The upper contains about 12 species belonging to 7 mammalian orders, and the lower has yielded one mammalian species and one reptilian species. Biostratigraphic, chemostratigraphic, and magnetostratographic study in the Lingcha Formation indicates that the transient carbon isotope excursion that marks the Paleocene–Eocene boundary as currently advocated is present in the upper Lingcha Formation. The fauna from the upper Lingcha Formation occurs within the excursion interval, and is of earliest Eocene age. It is correlative with the Wasatchian-0 faunal zone in the Big Horn Basin, Wyoming, North America. The lower Lingcha Formation is of Paleocene age.