Paleoecologies and paleoclimates of late cenozoic mammals from Southwest China: Evidence from stable carbon and oxygen isotopes
Paleoecologies and paleoclimates of late cenozoic mammals from Southwest China: Evidence from stable carbon and oxygen isotopes
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DOI：
10.1016/j.jseaes.2011.04.013
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发表时间：
2012-01-30
影响因子：
3
通讯作者：
Flynn, Lawrence
中科院分区：
文献类型：
--
作者：
Biasatti, Dana;Wang, Yang;Flynn, Lawrence
为了研究已灭绝类群的古饮食和栖息地，并了解长期的区域气候变化，我们测定了中国西南部云南省六个地点的食草动物牙齿化石和土壤样本的碳和氧同位素组成，这些样本的年龄从大约10Ma到现在。尽管空间和时间覆盖范围有限，但这些初步结果揭示了过去 1000 万年来哺乳动物类群的环境和饮食发生了重大变化。在 2-3 Ma 之前，虽然大多数受检查的哺乳动物都吃纯或接近纯的 C-3 饮食，但有些个体食用少量的 C-4 草（高达 20% C-4）。从那时起，C-4 草成为大多数食草动物的重要饮食成分，更新世元谋组和香格里拉的釉质三角洲 C-13 值较高，这很可能反映了该地区 C-4 生物量的增加。碳同位素结果表明，香格里拉2.5-1.75 Ma类似哺乳动物的饮食范围为纯C-3到纯C-4，而元谋1.7 Ma马的饮食中C-4草含量为0-70%。元谋和陆丰地区生活在8-7 Ma的哺乳动物的饮食和栖息地非常相似，气候条件也相似。与 3-4 Ma 类似后 C-4 生物量的增加表明区域气候的某些方面发生了显着变化，例如降雨的季节性增加或季节性干旱和火灾的增加，因为这些因素对现代草原很重要。数据还显示，与印度次大陆的斯瓦利克动物群不同，喜马拉雅-青藏高原东南侧的云南哺乳动物直到大约3-4 Ma都生活在以茂密森林为主的环境中。尽管如此，古土壤碳酸盐和化石釉质的δ C-13值都表明，元谋地区在中新世末期和上新世末期（约8-3.5 Ma）就存在C-4草，可能存在于森林冠层破碎或洪泛平原上的大分散、小斑块的开阔生境中，并且在约3.5 Ma后，C-4生物量显着增加。元谋（小河组）的氧同位素结果在大约8.5 Ma后显示出正变化，这在时间和幅度上与在临夏盆地的马和犀牛以及巴基斯坦和尼泊尔的化石和古土壤中观察到的Delta O-18变化相似，表明西藏东北部、东南部和南部边界的气候向干燥转变 中新世晚期的高原。综合起来，碳和氧同位素数据表明，随着时间的推移，当地气候普遍干燥，元谋地区从大约8 Ma的茂密森林环境转变为3-4 Ma之后的森林和草原镶嵌的更加开放的环境。元谋个体化石牙齿内的齿内三角洲 C-13 和三角洲 O-18 变化表明，与中新世晚期相比，降雨的季节性更强，约为 1.7 Ma。在云南哺乳动物牙齿中观察到的三角洲C-13和三角洲O-18的时空变化可能反映了区域气候和/或构造的变化，但需要更多的数据来充分探讨三角洲(18)O和三角洲C-13数据中的区域模式与该地区气候和构造演化的关系。 (C) 2011 Elsevier Ltd. 保留所有权利。
To examine paleodiets and habitats of extinct taxa and to understand long-term regional climate change, we determined the carbon and oxygen isotopic compositions of fossil herbivore teeth and soil samples from six localities in Yunnan Province, Southwest China, ranging in age from similar to 10 Ma to the present. Although limited in spatial and temporal coverage, these initial results reveal significant changes in the environments and diets of mammalian taxa over the last 10 million years. Prior to 2-3 Ma, while most mammals examined had pure or nearly pure C-3 diets, some individuals consumed a small amount of C-4 grasses (up to 20% C-4). Since then, C-4 grasses became a significant dietary component for most herbivores as indicated by higher enamel-delta C-13 values in the Pleistocene Yuanmou Formation and at Shangri-La, most likely reflecting an increased C-4 biomass in the region. The carbon isotope results show that the diets of mammals of similar to 2.5-1.75 Ma from Shangri-La ranged from pure C-3 to pure C-4 while 1.7 Ma horses from Yuanmou had 0-70% C-4 grasses in their diets. Mammals living at similar to 8-7 Ma in the Yuanmou and Lufeng region had very similar diets and habitats, with similar climatic conditions. Increased C-4 biomass after similar to 3-4 Ma suggests a significant change in certain aspects of regional climate, such as increased seasonality of rainfall or an increase in seasonal drought and fires as these factors are important to modern grasslands. The data also show that unlike the Siwalik fauna in the Indian subcontinent, mammals in Yunnan on the southeast side of the Himalayan-Tibetan Plateau lived in an environment dominated by dense forests until similar to 3-4 Ma. Nonetheless, both delta C-13 values of paleosol carbonates and fossil enamels indicate that C-4 grasses were present in the Yuanmou region in the latest Miocene and Pliocene (similar to 8-3.5 Ma), likely in greatly dispersed, small patches of open habitats where the forest canopy was broken or on flood plains, and the C-4 biomass increased significantly after similar to 3.5 Ma. The oxygen isotope results from Yuanmou (Xiaohe Formation) show a positive shift after similar to 8.5 Ma, which is similar in timing and magnitude to delta O-18 shifts observed in horses and rhinos from the Linxia Basin and in fossils and paleosols from Pakistan and Nepal, suggesting a shift toward a drier climate at the northeast, southeast, and southern borders of the Tibetan Plateau during the late Miocene. Taken together, the carbon and oxygen isotope data indicate a general drying of the local climate over time and a change from a largely dense-forest environment at similar to 8 Ma to a more open environment with a mosaic of forests and grasslands after 3-4 Ma in the Yuanmou region. Intra-tooth delta C-13 and delta O-18 variations within individual fossil teeth from Yuanmou suggest a stronger seasonality of rainfall at similar to 1.7 Ma than in the late Miocene. The spatial and temporal delta C-13 and delta O-18 variations observed in mammalian teeth from Yunnan likely reflect changes in regional climate and/or tectonics, but more data are needed to fully explore the significance of the regional patterns in the delta(18)Oand delta C-13 data in relation to climate and tectonic evolution of the region. (C) 2011 Elsevier Ltd. All rights reserved.