青藏高原:从热带动植物乐土到冰期动物群摇篮

Tibetan Plateau: From Paradise of Tropical Animals and Plants to Cradle of Ice Age Mammalian Fauna

在我国藏北渐新世地层中发现了攀鲈和鲃类新属种,其现生近缘类型都生活在亚洲和非洲的热带地区。这不仅在鱼类的系统发育和动物地理上具有重要意义,并且表明青藏高原腹地在距今26 Ma前仍然为温暖湿润的低地,伴生的棕榈、菖蒲等植物化石也指示同样的环境,说明当时由印度洋来的暖湿气流至少可以深入到藏北地区。自那时起,高原内部的地理特征与自然环境经历了巨大的变化。青藏高原在中新世持续隆升,至上新世达到现代高度,形成冰冻圈环境。在札达盆地的上新世沉积中发现了披毛犀、雪豹、北极狐和盘羊的祖先类型,显示适应严寒环境的第四纪冰期动物群起源于青藏高原,由此提出和进一步完善了寒冷适应性动物起源与扩散的"走出西藏"理论。

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 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 hur0id 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 modem 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.