Abstract:

The Early Oligocene is a critical time for global climate changes in the Cenozoic. This epoch witnessed severe mammalian faunal turnovers known as “Grande Coupure” in Europe and “Mongolian Remodelling” in Asia. However, insights about morphological changes in Oligocene mammal lineages have not been explored in detail. One of the least diversified groups of recent mammals, lagomorpha, is globally common in the fossil records, especially in Asia. During the Oligocene, many Eocene archaic lagomorph taxa died out and were replaced by more advanced forms. New findings from Nei Mongol and re-examination of the specimens from older collections enabled a revision of a common Asian lagomorph genus, Ordolagus, which possibly has a close affinity with the Middle-Late Eocene genus Gobiolagus. In Nei Mongol, we recognized the presence of Ordolagus during the basal Early Oligocene. Comparisons with coeval and slightly older lagomorph taxa from Asia and North America show that Ordolagus attained some salient tooth morphological characters (i.e., development of anteroconid on p3, full hypselodonty of cheek teeth, and lingual connection of trigonid and talonid on p4-m2), which are also the key features of modern leporids. The appearance of those morphologic features in Ordolagus is coeval to major global or regional climatic changes. Further investigations on Asian early lagomorphs compared with the study of other small mammals and local climatic factors will be essential to refine the role of lagomorphs as palaeoclimatic proxies.

Key words: Nei Mongol, northern China, Paleogene, Leporidae, taxonomy, evolutionary trends, convergence patterns, aridity/climate deterioration

摘要：

早渐新世是新生代全球气候变化的关键时期。这一时期发生了重大的哺乳动物群转换事件,在欧洲称之为 “大间断”, 在亚洲则为 “蒙古重建”。然而,关于渐新世哺乳动物各谱系的形态变化尚缺少详细探讨。兔形目是现代哺乳动物中多样性最低的类群之一,在全球的化石记录中很常见,尤其是在亚洲。渐新世时,许多古老的始新世兔形类灭绝并被更进步的类群所取代。内蒙古的新发现及对老标本的再研究使我们得以修订鄂尔多斯兔(Ordolagus) (亚洲常见的兔形类,可能源自中-晚始新世的戈壁兔Gobiolagus)。在内蒙古,我们识别出Ordolagus在早渐新世初期就已存在。与亚洲和北美的同期或稍早的兔形类的对比表明,Ordolagus具有一些显著的牙齿形态特征(p3下前边尖发达,颊齿完全高冠,p4-m2下三角座和下跟座舌侧相连等), 这些也是现生兔形类的主要特征。Ordolagus中这些特征的出现与重大全球或区域气候变化同步。对亚洲早期兔形类的进一步研究,并参考其他小哺乳动物与区域气候因素的研究,将有助于完善兔形类作为古气候代用指标的作用。

关键词: 内蒙古, 古近纪, 兔科, 分类学, 演化趋势, 趋同模式, 干旱化/气候恶化