中国北方哺乳动物群在中中新世气候适宜期的记录和表现

RECORDS AND CHARACTERISTICS OF THE MAMMALIAN FAUNAS OF NORTHERN CHINA IN THE MIDDLE MIOCENE CLIMATIC OPTIMUM

哺乳动物的起源和演化无不受其生活环境的调控和制约，因此化石物种及其组合的特点与变化是反映气候环境变化的重要标志之一。东亚的哺乳动物群在晚新生代期间经历了多次重大的转换，中新世中、晚期之交即发生了一次剧烈的动物群演替事件，适应于森林环境的铲齿象动物群被适应于草原环境的三趾马动物群所取代。中中新世全球气候变化也达到一个顶峰，南极冰量显著减少，大洋底层水温度进一步上升，形成17~15Ma期间的中中新世气候适宜期（Middle Miocene Climatic Optimum，简称MMCO），代表了地质历史时期与人类活动无关的一次强烈的增温事件。中国中中新世的哺乳动物群对MMCO的升温事件有敏感的响应，出现了大量喜暖喜湿的哺乳动物，如铲齿象、上猿、河狸、睡鼠、安琪马、爪兽、库班猪、利齿猪和古麟等。中中新世的铲齿象动物群反映了相当暖湿的气候环境，上猿等典型的森林动物在此背景下甚至分布到新疆、甘肃、宁夏、内蒙古等中国的北方地区。尽管中国的中中新世哺乳动物群几乎都产自河湖相沉积中，尤其以河流相的砂岩为主，保存为化石的机会较少，但仍然有充分的材料显示出哺乳动物对温暖湿润环境的适应性状，从而有足够的记录来描绘哺乳动物在MMCO期间的表现和响应。

The origin and evolution of mammals must be controlled and constrained by their living environments, so the characteristics and variations of their fossil species and assemblages are one of important signals reflecting the climatic and environmental changes. The East Asian mammalian faunas underwent several significant turnovers during the Late Cenozoic. There was a dramatic turnover event of mammalian faunas in the transition between the Middle and Late Miocene, namely, the forest-adapted Platybelodon fauna was replaced by the grassland-adapted Hipparion fauna. The global climatic change peaked in the Middle Miocene with the marked reducing of Antarctic continental ice-sheets and the further rising of ocean bottom temperatures, so that the Middle Miocene Climatic Optimum（MMCO）was formed from 17Ma to 15Ma, representing a major warming event irrelative to human activities in the geological time. The Middle Miocene mammalian faunas in China had sensitive responses to the MMCO warming event, so a large number of warm- and wet-adapted mammals appeared, such as Platybelodon, Pliopithecus, beavers, dormice, Anchitherium, Chalicotherium, Kubanochoerus, listriodonts, and Palaeotragus. The Middle Miocene Platybelodon fauna reflected relatively warm and wet climate and environment, and Pliopethecus and other typical forest animals dispersed even into Xinjiang, Gansu, Ningxia, and Inner Mongolia of North China under this background. Although almost all of the Chinese Middle Miocene mammalian faunas are preserved in fluvial and lacustrine deposits, especially fluvial sandstones, lacking dense fossils concentrations, there are sufficient materials to show the adaptive characteristics of mammals to warm and wet environments, thus there are enough records to display the behavior and response of mammals during the MMCO.