Palaeogene Sequoia leaves from Yunnan Province, China and their biogeographical significance

Sequoia was widely distributed across the Northern Hemisphere during the Cenozoic, yet our understanding of its biogeographic history remains limited due to relatively scarce fossil records in certain regions, particularly East Asia. A new Sequoia leaf fossil record from the Late Eocene to Early Oligocene in Yunnan Province of southwestern China displays morphological similarity to the fossil species S. maguanensis , such as an alternate leaf arrangement with a decurrent base, straight epidermal cell walls, and stomata surrounded by four subsidiary cells. Using the MaxEnt model and S. sempervirens (the only extant species of Sequoia ) as a reference, we identified optimal potential distribution areas for Sequoia from the Palaeocene to the Pliocene. Our results indicate that Sequoia , which thrived in warm and humid conditions, progressively shifted its range southward as global temperatures declined from the Eocene to the Pliocene, contracting its habitat towards lower latitudes. Our analysis suggests that Sequoia likely originated in East Asia during the Early Cretaceous and subsequently spread to North America via the Bering Land Bridge. During the Palaeocene, it extended its range to Greenland and Svalbard, eventually reaching western Europe during the Eocene. In the Oligocene, Sequoia was widespread across Europe and reached Siberia, later expanding from East Asia to the Mediterranean and northern Thailand by the Miocene. Quaternary glaciations led to its near-complete disappearance in Eurasia and North America, with only remnant populations surviving along the western coast of the United States. This study also highlights the role of morphological stasis in Sequoia alongside the intensification of the monsoon climate as key factors contributing to its eventual disappearance in southwestern China. • Sequoia fossils were discovered at a new location in Yunnan and identified as Sequoia maguanensis through comparison of morphological and cuticular features, providing new evidence for the distribution range of the Sequoia during the late Eocene to early Oligocene. • Climate data from the distribution areas of extant Sequoia were collected, and through model simulations, the most suitable potential distribution areas were revealed, indicating the survival preferences of Sequoia. • Fossil records of Sequoia from different periods were incorporated into the models to infer the origin and dispersal pathways of Sequoia. • By combining the results of the most suitable potential distribution areas with the distribution of Sequoia fossils, the reasons for the gradual reduction and eventual disappearance of Sequoia in southwestern Yunnan, China, were analyzed.