专题：青藏高原综合科学研究进展（Protovis himalayensis）不仅将羊类的化石记录扩展到青藏高原的上新世，并且显示青藏高原（可能还包括天山—阿尔泰山）代表了盘羊的祖先生活地区，这一基干类群是所有盘羊现生种的最近共同祖先，并与冰期动物“走出西藏”的起源理论一致。原羊小于现生的亚洲盘羊，但与盘羊一样具有向后外侧弯曲的角心和部分发育的额窦，以及一些趋向于盘羊的过渡性状。原羊化石地点距一个由变质岩基底形成的古岛不远，在面临食肉动物捕猎者威胁时，这些悬崖峭壁可以为原羊提供保护的条件[24]。
札达盆地食草哺乳动物的化石碳同位素分析结果指示上新世时期 C3 植物在植被中占有统治地位[25]，说明原羊与青藏高原的现代牛科动物一样，也以 C3 植物为食。青藏高原的盘羊祖先与现代的盘羊占据相同的分布范围，在上新世已适应高海拔的寒冷环境，而当时的其他地区，包括高纬度的北极圈都处在更温暖的气候条件下。这一祖先类群快速进化到相似于现生盘羊的形态条件，在约距今 2.6 Ma 的第四纪冰期到来时，它们拥有了在冰冻环境下生存的竞争优势，因而迅速扩散到青藏高原周边以及更遥远的地区。
我们的研究结果表明，渐新世时期尼玛和伦坡拉等盆地的海拔高度不超过 2 000 m，整个青藏高原的地势还不足以阻碍大型动物的交流，巨犀（Paraceratherium）等哺乳动物仍然能够在高原南北之间穿行；到中新世，吉隆、伦坡拉和可可西里等盆地的数据反映高原上升至海拔 3 000 m 左右，已成为当时铲齿象（Platybelodon）等哺乳动物交流的屏障；直至上新世，札达和昆仑山口等盆地达到了 4 000 m 以上的现代海拔高度，由此形成冰冻圈环境，导致冰期动物群的出现（图 2）。长期以来，科学家一直在上新世和早更新世的极地苔原和干冷草原上寻找适应寒冷气候的第四纪冰期动物群的始祖，但并未获得成功。现在，通过对在青藏高原上以札达盆地为代表的新生代晚期沉积物中所发现的哺乳动物化石的研究，我们认识到，在上新世达到现代高度的青藏高
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原的严寒气候已经使第四纪冰期动物群的祖先们度过了寒冷适应进化的最初阶段。
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Tibetan Plateau: From Paradise of Tropical Animals and Plants to Cradle of
Ice Age Mammalian Fauna
Deng Tao1,2 Wang Xiaoming1,3 Li Qiang1,2 Wu Feixiang1
（1 Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology,
Chinese Academy of Sciences, Beijing 100044, China;
2 Center for Excellence in Tibetan Plateau Earth Sciences, Chinese Academy of Sciences, Beijing 100101, China;
3 Natural History Museum of Los Angeles County, Los Angeles, CA 90007, USA）
Abstract New genera and species of the climbing perch and cyprinine fish were discovered from the Oligocene strata in northern Tibet. On the other hand, all their extant close relatives live in the tropical regions of Asia and Africa. These discoveries not only are significant for
院刊 965
专题：青藏高原综合科学研究进展the phylogeny and zoogeography of fishes, but also imply that the hinterland of the Tibet area was a warm and humid lowland at 26 Ma as suggested by the co-existing plant assemblage including palms and golden rain trees among others, indicating that the warm and humid air current of the Indian Ocean could flow deeply into northern Tibet at least. Since that time, the geographical features and natural environments within the Tibetan Plateau have greatly changed. The Tibetan Plateau was consistently uplifted in the Miocene, and then reached its modern elevation in the Pliocene so that a cryosphere environment appeared. The ancestor forms of the woolly rhino, snow leopard, arctic fox, and bighorn sheep were discovered from the Pliocene deposits in the Zanda Basin, which showed that the frigid-adapted Quaternary Ice Age fauna originated in the Tibetan Plateau. As a result, the Out of Tibet theory about the origin and expansion of cold-tolerated mammals were proposed and further improved.
Keywords Tibetan Plateau, paleo-elevation, tropical, Ice Age, fauna
新生代环境演变研究。他率领的团队在青藏高原及其周边地区发现的丰富脊椎动物化石证实高原自早中新世晚期开始显著隆升，所提出的“走出西藏”理论揭示青藏高原札达盆地的上新世哺乳动物群肇始了第四纪冰期动物群的寒冷适应性谱系，并证明青藏高原在该时期达到了现代高度。E-mail: dengtao@ivpp.ac.cn
邓 涛 中科院古脊椎动物与古人类研究所副所长、研究员，长期从事奇蹄类哺乳动物演化、新近纪陆相地层对比和晚
Deng Tao Deputy director and research professor of Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences. He has long-term research interests to focus on the evolution of perissodactyl mammals, the Neogene terrestrial stratigraphy, and the late Cenozoic environmental changes. He and his team discovered rich vertebrate fossils from the Tibetan Plateau and its surrounding areas to imply a high plateau since the late Early Miocene. Their “Out of Tibet” theory has revealed that the Pliocene mammalian fauna of the Zanda Basin in the Tibetan Plateau showed initiation of cold-adapted lineages that predate Ice Age megafauna, which indicated that the Tibetan Plateau reached its modern elevation. E-mail: dengtao@ivpp.ac.cn
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