湖南杨二洞更新世晚期动物群研究

湖南花垣县杨二洞化石点位于沅江上游,动物群种类包括有6目26种,动物群时代为晚更新世末期。杨二洞小型哺乳动物化石材料较多。有些小型哺乳动物在我国更新世时期首次发现,如大爪长尾鼩、大黑伏翼、大齿鼠等。杨二洞动物群在我国西南地区更新世末期的材料之中,具有较为突出的森林性特征,反映出湘西北更新世末期具有南亚热带森林古环境。动物群综合研究发现,小家鼠、褐家鼠在中更新世晚期分别产生于中国东北和长江下游,其中小家鼠在更新世晚期经华北向长江流域及其以南扩散,褐家鼠在更新世较晚时期分别向华北和岭南扩散。晚更新世以来,有较多小哺乳动物出现了从低海拔向高海拔山区进行生境转移的现象,这种生境转移对认识大熊猫生态演变有重要参考。杨二洞堆积物特征反映,沅江上游晚更新世末期时河床侵蚀性下切明显,地貌变化显著。

LATE PLEISTOCENE FAUNA AT YANG′ER CAVE IN HUNAN PROVINCE

The study areas in this paper cover South West China,North East China,North China,and the Changjiang River drainage region.Focused on mammal fossils from the Yang′er Cave in Huayuan County of Hunan Province,we also analyzed various mammal fossil species of Pleistocene Epoch found in other sites in North East China,North China,and the middle and lower reaches of Changjiang River.Among the fauna some small mammals such as Soriculus nigrescens,Arielulus circumdatus and Dacnomys millardi first appeared in Pleistocene records in China.The integrated research of zooecology and evolution showed that Yang′er Cave fauna was of typical forest traits in Late Pleistocene in South West China.The rare species Soriculus nigrescens today inhabiting in the South Tibetan Everest and in snow mountain areas of West Yunnan Province with altitudes ranging from 2200 meters to 3400 meters,lived in Late Pleistocene in the northwest of Hunan Province(i.e.Yang′er Cave)with the altitude of only 319 meters.This demonstrated that the habitats for Soriculus nigrescens shifted a great deal from Late Pleistocene to Holocene,which was very similar to that for giant pandas.It confirms that such a kind of habitat shift are not unique to giant pandas.Many animals widely lived in the south of China in Pleistocene Epoch,while in Holocene they moved up to certain mountain areas with high altitude in South West China.This phenomenon is even more distinct for some species of small mammals,e.g.Soriculus nigrescens,Mus musculus,and Rattus norvegicus,which now are widely distributed all over the world.They first appeared in North East China and the lower reaches of Changjiang River in the late stage of Middle Pleistocene.Mus musculus expanded via North China to Changjiang drainage areas as well as more south areas in late Pleistocene.Rattus norvegicus in the same time expanded to North China and Lingnan area respectively.The research on Yang′er Cave provides more new identification data,and draws a conclusion of some new important identification criteria from the research results of specimen modality.For example,for the first time the cognizance is obtained on many measuring indexes of Soriculus nigrescens's fossil specimen mandibular(e.g.the length of mandibular iS ₁7.81mm,the length of lower cheek tooth row is 6.61mm,the length between lower canine and molar is 7.56mm,the length of lower molar series is 5.80mm,etc.).The newly-found mandibular fossil of Dacnomys millardi presents a simple chewing surface structure of lower molar series and by the side of the lip there is no style.The depositional features of Yang′er Cave also manifested remarkable changes of river bed in the upper reaches of Yuanjiang River since the Late Pleistocene.