First fossil woods and palm stems from the mid-Paleocene of Myanmar and implications for biogeography and wood anatomy.

Abstract

The rise of angiosperm-dominated tropical rainforests has been proposed to have occurred shortly after the Cretaceous-Paleogene transition. Paleocene fossil wood assemblages are rare yet provide important data for understanding these forests and whether their wood anatomical features can be used to document the changes that occurred during this transition. We used standard techniques to section 11 fossil wood specimens of Paleocene-age, described the anatomy using standard terminology, and investigated their affinities to present-day taxa. We report here the first middle Paleocene fossil wood specimens from Myanmar, which at the time was near the equator and anchored to India. Some fossils share affinities with Arecaceae, Sapindales (Anacardiaceae, Meliaceae) and Moraceae and possibly Fabaceae or Lauraceae. One specimen is described as a new species and genus: Compitoxylon paleocenicum gen. et sp. nov. This assemblage reveals the long-lasting presence of these aforementioned groups in South Asia and suggests the early presence of multiple taxa of Laurasian affinity in Myanmar and India. The wood anatomical features of the dicotyledonous specimens reveal that both "modern" and "primitive" features (in a Baileyan scheme) are present with proportions similar to features in specimens from Paleocene Indian localities. Their anatomical diversity corroborates that tropical flora display "modern" features early in the history of angiosperms and that their high diversity remained steady afterward.