Early Oligocene Podocarpium (Leguminosae) from Qaidam Basin and its paleoecological and biogeographical implications

Abstract

The extinct legume genus Podocarpium first appeared in the middle Eocene of South China and then became widely distributed throughout Eurasia during the Oligocene and Miocene. Fossil records from Central Asia are important for understanding the patterns of floristic change of Podocarpium between Eastern Asia and Europe, but they are relatively rare. Here, we describe well-preserved fossil fruits and leaves of Podocarpium podocarpum (A. Braun) Herendeen from the early Oligocene (Rupelian) of the Qaidam Basin, northwest China. Morphological comparison among fossil fruits of all Podocarpium reported so far confirms the difference in fruit shape between Podocarpium eocenicum and P. podocarpum, and shows a decrease in fruit size during the Oligocene, which might be a response from this thermophilous plant to a cooler condition. The presence of P. podocarpum in the early Oligocene of Qaidam suggests that the Qaidam Basin might play an important role in the migration of this genus between Eastern Asia and Europe during the early Oligocene. Moreover, the expansion of Podocarpium in China during the Cenozoic appears to be strongly influenced by the East Asia monsoon development.