Fossil woods from the middle Miocene of Myanmar: implications for the evolution of Dipterocarpaceae
Résumé
The paleobotanical record of Myanmar is poorly documented despite its importance for understanding the evolution of Asian rainforests, often dominated today by Dipterocarpaceae. The middle Eocene of Myanmar has yielded some of the earliest Dipterocarpaceae of the paleobotanical record, associated with seasonally dry forests that are today common in monsoonal areas of India. Here, we describe 17 species of fossil woods (including 4 new species) collected in the middle Miocene Natma Formation, central Myanmar. These species share affinities with modern Fabaceae, Dipterocarpaceae, Burseraceae, Moraceae and Cupressaceae. They include a great variety of fossil dipterocarps (7 species) similar to the one found in modern rainforests of peninsular Southeast Asia. The presence of fossil dipterocarp species typical of wet evergreen forests contrasts with Burmese Eocene dry dipterocarp assemblages and indicates wetter conditions in the Miocene. Our paleoenvironmental reconstructions support a late Paleogene adaptation of dipterocarps to everwet ecosystems, as suggested by previous physiological and biogeographic studies.