Tibetan Plateau palm fossils prove the Kohistan-Ladakh Island Arc is a floristic steppingstone between Gondwana and Laurasia

Abstract

Palms are mainly distributed in the pantropical regions and although the fossil records are rich globally, their evolutionary and biogeographic histories remain unresolved largely due to the uneven spatial distribution of fossil records. Here, we report late Paleocene palm leaf fossils from Lazi County, southern Tibetan Plateau. These fossil leaves, characterized by induplicate fan-shaped costapalmate laminae with unarmed petioles, suggest an affiliation with the subfamily Coryphoideae. With morphological comparisons to other palm leaf fossil records, we place these palm leaf fossils within the fossil genus Sabalites, specifically Sabalites striatipetiolaphyllum Y. Gao et T. Su sp. nov. Together with previous palm fossil records, we propose that the Kohistan-Ladakh Island Arc served as a steppingstone for the dispersal of palms from India to southern Tibet by the late Paleocene, and palms spread into central Tibetan region by the late Eocene. Overall, palm fossils in this study provide crucial evidence for floristic interchange between India and Asia during the Paleogene, as well as a warm climate in southern Tibet at that time.