泥河湾盆地新发现的梅氏犀及裴氏板齿犀化石

在河北省阳原县大黑沟中更新世和岑家湾附近石沟早更新世地层中分别发现了犀牛的下颌骨和股骨化石。其下颌联合部窄长、无下门齿、牙齿釉质层平滑而无褶皱、牙齿表面无垩质充填,股骨较披毛犀的长,故将其归入梅氏犀(Stephanorhinus kirchbergensis)。泥河湾盆地的化石是我国早期梅氏犀化石中材料最可靠,地点层位最明确的记录。山神庙咀和大黑沟出土的板齿犀牙齿及前脚骨化石,是泥河湾盆地发现的最好材料,尤其是大黑沟出土的板齿犀牙齿化石,是迄今在泥河湾盆地首次发现的完整材料;依据冠面结构和测量数据,该批材料可归入裴氏板齿犀(Elasmotherium peii);裴氏板齿犀特征鲜明,是有效名称,我国早更新世的板齿犀均应归入该种。我国第四纪的板齿犀与高加索板齿犀之间存在显著差异,表现在釉质层厚度较大但褶皱不够强烈、下颊齿的下后尖发育、颊齿冠面的前后径多数大于颊舌径、M3比M2小、M3后附尖欠发育,后脊与外脊已完全融合、上颊齿的齿脊更厚。此外,我国的板齿犀与西伯利亚板齿犀也有差异,后者的牙齿齿冠更高、无齿根、釉质层薄且褶皱强烈、上颊齿无后窝。最新地层研究表明,我国含板齿犀属的地层时代不晚于早更新世,且集中出现于下更新统。在晚新生代期间,犀牛在泥河湾盆地十分常见,先后出现过如下属种:大唇犀(Chilotherium sp.)(上新世)、裴氏板齿犀(Elasmotherium peii)(早更新世)、泥河湾披毛犀(Coelodonta nihowanensis)(早更新世)、梅氏犀Stephanorhinus kirchbergensis(早-中更新世)和真披毛犀(Coelodonta antiquitatis)(中-晚更新世)。

New Fossils of Stephanorhinus kirchbergensis and Elasmotherium peii from the Nihewan Basin

Rhinoceros mandibles and femora from Daheigou and Shigou were collected from Middle and Early Pleistocene strata, respectively. The specimens were attributed to Stephanorhinus kirchbergensis (=Stephanorhinus mercki) based on the following characters: constriction of the symphysis; lack of incisors; smooth enamel layer without cementum; and a long femur. The fossils of Stephanorhinus kirchbergensis herein reported represent the definite earliest record with certain provenance of this species in China. The teeth and foot bones of Elasmotherium from Shanshenmiaozui and Heitugou represent the best fossil materials ever recovered in the Nihewan Basin. In particular, tooth specimens are the first discovery in the Nihewan Basin. Based on dental morphology and dimensions, the elasmothere fossils recently discovered can be referred to the species Elasmotherium peii. The authors propose here that Elasmotherium peii is a valid species name and that all Early Pleistocene elasmothere fossils in China can be included in this species. The Quaternary elasmothere in China is quite different from those of the Caucasian region in the following aspects: thicker but less crimped enamel layer; metaconid much more developed; more elongated upper teeth; smaller M3 compared to M2; less developed metastyle; metaloph fused with ectoloph in M3; and lophs more developed in upper teeth. In addition, Chinese materials are also different from Elasmotherium sibiricum in their relatively less hypsodont teeth, thicker enamel and prominent roots. Recent biostratigraphic studies show that the Elasmotherium-bearing strata are Early Pleistocene in age. Since the Pliocene onward, the following rhinoceros taxa occurred in the Nihewan Basin: Chilotherium sp. (Pliocene), Elasmotherium peii (Early Pleistocene), Coelodonta nihowanensis (Early Pleistocene), Stephanorhinus kirchbergensis (Early to Middle Pleistocene) and Coelodonta antiquitatis (Middle to Late Pleistocene)