The Cenozoic history of palms: Global diversification, biogeography, and the decline of megathermal forests

Aim: Megathermal rainforests and mangroves are much smaller in extent today than in the early Cenozoic, primarily due to global cooling and drying trends since the Eocene--Oligocene Transition (~ 34 Ma). The general reduction of these biomes is hypothesized to shape the diversity and biogeographic history of tropical plant clades. However, this has rarely been examined due to a paucity of good fossil records of tropical taxa and the difficulty in assigning them to modern clades. Here, we evaluate the role that Cenozoic climate change may have played in shaping the diversity and biogeography of tropical plants through time. Location: Global. Time period: Cenozoic, 66 million years ago to present. Major taxa studied: Four palm clades (Calaminae, Eugeissoneae, Mauritiinae, and Nypoideae), and their fossil pollen record. Methods: We compiled fossil pollen occurrence records for each focal palm lineage to reconstruct their diversity and biogeographic distribution throughout the Cenozoi...