The late Eocene pine seed cones from Mangkang Basin, southeastern Xizang (Tibet) and their biogeographic significance

Pinus is widely distributed in the Northern Hemisphere, and today is the largest gymnosperm genus with a rich fossil record. However, the biogeographic history at section or subsection level remains unclear. Here, we report a new finding of female cones from the late Eocene of the Mangkang Basin, southeastern Xizang (Tibet). By morphological comparison between fossil and extant species, this cone type is identified as a new species in subsection Pinus, namely Pinus mangkangensis Yao and Su, n. sp. This new species is morphologically similar to the living species P. yunnanensis, which is distributed in Southwest China adjacent to the fossil site. The finding of P. mangkangensis provides important evidence for elucidating the biogeographic history and diversification of subsection Pinus in Southwest China. Together with other fossil records of section Pinus in East Asia, we propose that P. mangkangensis represents southern lineages and suggests that ancestral species of subsection Pinus dispersed to lower latitude regions during the Eocene. Subsequently, the diversification of species in subsection Pinus took place during the Miocene.