Fossil woods from the lower Miocene of Myanmar (Natma Formation):
paleoenvironmental and biogeographic implications
Abstract
The paleobotanical record of Myanmar is poorly documented despite its
importance for understanding the evolution of Asian monsoonal ecosystems
through time. Here, we describe seventeen species of fossil wood from
silicified specimens collected in the upper lower to lowermost middle
Miocene Natma Formation, central Myanmar. These species share affinities
with modern Fabaceae, Dipterocarpaceae, Burseraceae, Moraceae and
Cupressaceae. Five new species are described, belonging to genera
Koompassioxylon Kramer (K. kalewensis n. sp.), Pahudioxylon Chowdhury,
Ghosh & Kazmi (P. adenantheroides n. sp.), Dipterocarpoxylon (Holden)
Den Berger (D. fugax n. sp.), Shoreoxylon Den Berger (S. glomeratum n.
sp.), Artocarpoxylon Prakash & Lalitha (A. informe n. sp.). They
include the first record of genus Dryobalanoxylon Den Berger in Myanmar,
as well as a great variety of fossil dipterocarps (7 species) as found
in today’s Southeast Asian rainforests. The nearest living relatives of
this assemblage reflect different ecotones of seasonal forests with
coastal, mixed to dry deciduous, and wet evergreen species. This
reconstruction implies a wet, warm, and monsoonal climate in Myanmar
during the late early Miocene. The presence of fossil dipterocarp
species typical of wet evergreen forests contrasts with Burmese Eocene
dry dipterocarp assemblages and indicates wetter conditions during the
Miocene. Our reconstructions support a long-term change from seasonal to
everwet ecosystems for dipterocarp trees.