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陕西蓝田晚中新世灞河组的仓鼠化石

2008年 第46卷 第4期:307~316

发表日期:2008-11-07李志恒来源:放大 缩小

编辑:张兆群  郑绍华  刘丽萍

摘要:陕西蓝田是我国晚中新世地层发育最完整的地区之一。新近纪哺乳动物分期中的灞河期即根据该地区灞河组发现的化石而命名。1997至2001年度的中芬合作在灞河组发现大量的新层位与化石标本。连续的地层剖面与大量的化石资料为进一步认识晚中新世哺乳动物的演化历史提供了很好的基础。
    灞河组发现的仓鼠可以归入两个属:微仓鼠Nannocricetus和科氏仓鼠Kowalshia。微仓鼠的分布时限较长,从灞河组的底部到中上部层位,古地磁研究指示其年代为10. 2~8 Ma。根据形态特征与测量数据,发现的微仓鼠标本被归入同一种Nannocricetus primitivus。其主要特征有:个体很小;m1的下前边尖在中度或重度磨蚀的标本上呈单尖,metalophulid I存在,但metalophulid II缺如;M1前边尖与原尖单连接;M3很退化。与Nannocrietus mongolicus相比,m1的下前边尖更少分开,且在唇侧有向后延伸的弱脊,下前小脊很弱或缺失,rn2的舌侧前边尖较发育,M1前边尖与原尖单连接,M3次尖较发育且缺失后尖。推测Nannocricetus primitivusN.mongolicus直接祖先类型,向后者转换的时间大约发生在7~8 Ma。
    根据新的化石材料重新修订了微仓鼠的属征:个体很小的仓鼠;上臼齿的中脊与下臼齿的下中脊完全缺失或极不发育;m1下前边尖呈单尖或较少分开;m2的下次尖靠舌侧,使得m2的后部较窄,m2中原谷向前延伸不太远;M3很退化。
    科氏仓鼠的标本很少,仅发现在剖面的上部,其时代稍早于8 Ma,与云南禄丰的年代大致相当,是目前中国发现的最早纪录之一。推测科氏仓鼠在8 Ma前从欧洲迁移至中国。

关键词:陕西蓝田,晚中新世,灞河组,仓鼠

卷期:46卷 04期

  Late Miocene Cricetids from the Bahe Formation, Lantian, Shaanxi Province 

  Zhang Zhao-Qun , ZHENG Shao-Hua, LIU Li-Ping 

    
Abstract  Fossil cricetids found from the Bahe Formation, Lantian are assigned to Nannocricetus primitivus sp. nov. and Kowalskia indet. respectively by their dental characters and measurements. The new species Nannocricetus primitivus is characterized by its smaller size and having single cusped anteroconid of m1 on moderate and heavily worn teeth, presence of metalophulid I, absence of metalophulid II, no mesoloph on upper molars, absent or very weak mesolophid on lower molars, and very reduced M3. Magnetostratigraphic results of the Bahe Formation indicate that the localities produced Nannocricetus primitivus range from the early Late Miocene to the middle Late Miocene (~10.2?8 Ma). The primitiveness of the new species and its earlier geologic records suggest that it might be the direct ancestor of Nannocricetus mongolicus. The turnover from Nannocricetus primitivus to N. mongolicus should occur at about 7~8 Ma. There found only one m2 of Kowalskia. The fossil level of Kowalskia indet. is in the upper part of the main section, dated to slightly earlier than 8 Ma. Except the material from Lufeng (MN11), the Lantian material is one of the earliest emigrants from the western Eurasia. 
Key words  Lantian, Shaanxi; Late Miocene; Bahe Formation; Cricetidae 

 

 

 

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