陕西洛南古新世湖口兽头骨

A MESONYCHID (MAMMALIA) SKULL FROM THE PALEOCENE OF LAONAN, SHAANXI

本文记述的是湖口兽属的一头骨化石,代表了该属的一个新种。湖口兽属是踝节目的成员,化石最早发现在广东省南雄县湖口公社,所在地层时代是中古新世。

This paper deals with a new species of Mesonychid, Hukoutherium shimemensis sp. nov., secured in the Yanghe Brigade, Shimemen Commune, Laonan County, Shaanxi Province on the southern slope of Qingling Ridge in the autumn of 1978. Hukoutherium which belongs to Condylarthra was first discovered in the middle Paleocene of Nanxiong Basin of Guangdong province. The discovery of the new species in Shaanxi indicates that there exists paleocene strata, and provides good material for the study of contemporary ancient mammals. Hukoutherium Chow, Zhang, Wang et Ding, 1973 Type species: Hukoutherium ambigum Chow et al., 1973 Known Distribution: Middle Paleocene of Asia. Revised Diagnosis: Medium-sized mesonychids; the facial and cranial parts of the skull nearly of the same hight and length, the posterior area of the obrit compressed transversely, the sagittal crest much higher, the zygomatic arch extends far laterally; the mandibular horizontal ramus flat long, the condyle lower, on the same level as the chcek teeth row; tooth formula: I_3^(3(?)), C_1~1 P_4~4, M_3~3; canines large, stout, tusk-like with ends curved backward, premolars simple, conical, uper molars wide transversely with vestigial metacones, M_3~3 reduced, talonid of M_3 crested. Hukoutherium shimemensis sp. nov. Type: A poorly preserved skull with rather perfect outline, associated with lower jaws, most of the cheek teeth on each side of upper and lower jaws preserved (v 6260). Diagnosis: A mesonychid somewhat smaller than Hukoutherium ambigum, the anterior part of the mandible not steep, the symphysis very narrow, the distance between the two lower canines extremely short, lower premolars simple with apexes straight upward, M_3 with long talonid, cingulum undeveloped. Hukoutherium shimemensis similar to H. ambigum in most of morphology, and sedimentary series of the Shimem Basin also similar to those of the Nanxiong Basin in lithologic facies lead us to the conclusion that the deposits in both Basins are the same in age——Middle paleocene. Thus Shimen section is the first one of paleocene in Shaanxi Province.