EVALUATING THE ROLE OF INDIA IN PLANT BIOGEOGRAPHY: EXAMPLES FROM FOSSIL PALM FRUITS FROM THE DECCAN INTERTRAPPEAN BEDS

Palms have a rich and geographically extensive fossil record that stretches back to the Late Cretaceous. Their distinctive morphology and anatomy, narrow environmental range, and continuous fossil record make them a model group of plants for addressing questions on plant evolution, biogeography, and terrestrial environments over the Late Cretaceous and Cenozoic. The Maastrichtian-Danian Deccan intertrappean beds (DIB) host a particularly rich fossil palm assemblage, from which more than 140 species have been described since the early 1930s based on isolated stems, leaves, roots, inflorescences, and fruits. Owing to the dynamic tectonic history of India, understanding the taxonomic affinities of these fossils may help shed light on biogeographic patterns in the radiation of palm lineages and the role that India played in these processes. We call attention to striking morphological and anatomical similarities between Arecoidocarpon, a common fossil fruit type in the DIB, and fruits of extant Orania (tribe Oranieae). Recognition of tribe Oranieae in India at the end of the Cretaceous has interesting biogeographic implications — Oranieae belongs to a clade of three monotypic tribes (POS clade) that is disjunctly distributed and absent today in India, with the tribes Podococceae and Sclerospermeae in Africa, while Oranieae occurs in New Guinea, parts of Southeast Asia, and Madagascar. The DIB fossils in question are much more similar to Oranieae than the African taxa in the POS clade. Various biogeographic scenarios based on ancestral area reconstructions have been proposed to explain the geographic distribution of the POS clade. These include (1) migration into Africa and the Indo-Pacific from Eurasia, and (2) dispersal of stem POS from South America into Africa, with tribe Oranieae spreading into the Indo-Pacific through India. The presence of Oranieae in India ~66 Ma pushes back divergence time estimates for the clade and supports the latter biogeographic hypothesis, indicating India may have played a role in the dispersal of the tribe into the Indo-Pacific. This is in contrast to other palms in the DIB assemblage, which include fruits belonging to modern South American and Asia-Pacific clades, indicating diverse biogeographic affinities of Deccan palms and broader historical ranges for some groups.