First fossil-leaf floras from Brunei Darussalam show dipterocarp dominance in Borneo by the Pliocene

• Published in: PeerJ (San Francisco, CA) CA), 2022-03, Vol.10, p.e12949-e12949, Article e12949
• Main Authors: Wilf, Peter, Zou, Xiaoyu, Donovan, Michael P, Kocsis, László, Briguglio, Antonino, Shaw, David, Slik, Jw Ferry, Lambiase, Joseph J
• Format: Article
• Language: English
• Subjects: Algae; Archipelagoes; Argentina; Australia; Beaches; Biodiversity; Biogeography; Borneo; Brunei; Cenozoic; China; Compression; Conservation; Dipterocarpaceae; Dominance; East Asia; Ecosystem; Ecosystem Science; Endangered & extinct species; Evolutionary Studies; Extinction (Biology); Ferns; Fossils; Humans; India; Indonesia; Leaves; Lianas; Malaysia; Mangrove swamps; Mangroves; Melastomataceae; New records; Paleobotany; Paleoenvironments; Paleontology; Plankton; Plant fossils; Plant Leaves; Plant Science; Plants; Pleistocene; Pliocene; Pollen; Protection and preservation; Rain forests; Rainforests; Spores; Surveys; Taphonomy; Taxonomy; United Kingdom
• ISSN: 2167-8359; 2167-8359
• DOI: 10.7717/peerj.12949

The Malay Archipelago is one of the most biodiverse regions on Earth, but it suffers high extinction risks due to severe anthropogenic pressures. Paleobotanical knowledge provides baselines for the conservation of living analogs and improved understanding of vegetation, biogeography, and paleoenvironments through time. The Malesian bioregion is well studied palynologically, but there have been very few investigations of Cenozoic paleobotany (plant macrofossils) in a century or more. We report the first paleobotanical survey of Brunei Darussalam, a sultanate on the north coast of Borneo that still preserves the majority of its extraordinarily diverse, old-growth tropical rainforests. We discovered abundant compression floras dominated by angiosperm leaves at two sites of probable Pliocene age: Berakas Beach, in the Liang Formation, and Kampong Lugu, in an undescribed stratigraphic unit. Both sites also yielded rich palynofloral assemblages from the macrofossil-bearing beds, indicating lowland fern-dominated swamp (Berakas Beach) and mangrove swamp (Kampong Lugu) depositional environments. Fern spores from at least nine families dominate both palynological assemblages, along with abundant fungal and freshwater algal remains, rare marine microplankton, at least four mangrove genera, and a diverse rainforest tree and liana contribution (at least 19 families) with scarce pollen of Dipterocarpaceae, today's dominant regional life form. Compressed leaves and rare reproductive material represent influx to the depocenters from the adjacent coastal rainforests. Although only about 40% of specimens preserve informative details, we can distinguish 23 leaf and two reproductive morphotypes among the two sites. Dipterocarps are by far the most abundant group in both compression assemblages, providing rare, localized evidence for dipterocarp-dominated lowland rainforests in the Malay Archipelago before the Pleistocene. The dipterocarp fossils include winged fruits, at least two species of plicate leaves, and very common leaves. We attribute additional leaf taxa to Rhamnaceae ( ), Melastomataceae, and Araceae ( ), all rare or new fossil records for the region. The dipterocarp leaf dominance contrasts sharply with the family's