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 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.