“Out-of-India” dispersal of the extinct fabaceous genus Podocarpium Braun ex Stizenberger

Abstract

Podocarpium is a well-known extinct single-seeded legume genus having extensive Cenozoic fossil occurrences from East Asia to central Europe. To date, there have been no fossil records of this genus from South Asia, including India. Here, we report and describe for the first time a well-preserved fossil pod from the early Eocene of Rajasthan, western India, assigned to extinct Podocarpium based on detailed morphology. It is characterized by an asymmetrical, oblique valve with a single oblong seed, a distinctly curved stipe, a wingless margin, a prominent vascular strand along the dorsal suture that anastomoses into the apex, a weakly curved ventral suture, fine reticulate veins, a short acuminate apex, and a narrowly acute base. This discovery is the oldest fossil evidence of Podocarpium recorded to date worldwide. Together with previous fossil records, we suggest an “Out-of-India” dispersal hypothesis to explain the biogeography of this extinct legume genus. It might have originated under warm and humid tropical climate conditions in the early Eocene of India (South Asia), then migrated to China (East Asia), and subsequently spread north and westward to Europe.