Significant shift in the terrestrial ecosystem at the Paleogene/Neogene boundary in the Tibetan Plateau

Abstract

<p indent=0mm>The shift from the Paleogene to the Neogene represents an important timeline in the history of life on Earth: A point when the biotic realm approached that of nature today. The uplift of the Tibetan Plateau in the Cenozoic Era has imposed profound influence on the evolution of the terrestrial ecosystem by creating a sustainable life system in a freezing climate. A reconstruction of this epic scene on the plateau relies on fossil discoveries. Based on a recent study of numerous well-preserved fossils from the Paleogene and Neogene deposits of the Lunpola and Nima basins in the central Tibetan Plateau, we recognized therein, for the first time, the turnover of the Late Oligocene tropical or subtropical ecosystem, and the subsequent transition toward a plateau-type biotic assemblage during the Early Miocene epoch. The fossil biota consisting of fishes, insects and plants from the Upper Oligocene suggests that in 26−24 Ma, the hinterland of the Tibetan Plateau was a warm and humid lowland nourished by tropical moisture from the Indian Ocean, which would have been able to reach northern Tibet then. This biota, represented by climbing perches and palms, shows typical tropical or subtropical climatic patterns and maintained a paleoelevation no higher than <sc>2300 m</sc> in the depositional areas. In the Early Miocene, the Tibetan ecosystem underwent comprehensive transformation into the one we recognize today. Primitive snow carps, which are endemic to the plateau today, emerged and, in an “Ascending with the Modifications” mode, evolved into more and more specialized species all the way up until the Pliocene epoch. The vegetation of the Early Miocene was dominated by temperate broad-leaved forests mixed with abundant coniferous trees and booming herbs, hence showing a cool climatic setting. Some mammals adapted to the temperate forest, e.g., <italic>Plesiaceratherium</italic> (a kind of extinct rhinos), appeared at the center of the plateau during the Early Miocene, and gave way to the ancestors of the Ice Age mammals, e.g., the woolly rhino of the Pliocene epoch. Such a dramatic transformation of the Tibetan ecosystem around the Paleogene and Neogene boundary was due to the cooling-down effect accompanying the rise of the main body of the plateau to ca. <sc>3000 m</sc> and the global climate evolution toward icehouse conditions during the Cenozoic.