Edward J. Spagnuolo, Peter Wilf, John-Paul Zonneveld, David Shaw, Aswan, Yan Rizal, Yahdi Zaim, Jonathan I. Bloch, Russell L. Ciochon
Premise of research. The Neogene collision of the Australian tectonic plate (Sahul) with Southeast Asia (Sunda) restructured the vegetation of both regions. The rarity of plant macrofossils from Sunda has limited the understanding of precollision vegetation and plants that migrated from Sunda to Sahul. Despite the importance of legumes in the living flora, no Malesian reproductive or pre-Neogene fossils of the Fabaceae are known. Methodology. We collected 47 plant macrofossils from the Tambak Member of the Tanjung Formation (middlelate Eocene) while surveying the Wahana Baratama coal mine near Satui, South Kalimantan, Indonesian Borneo. These fossils represent Southeast Asian forests before the Sahul-Sunda collision. We studied three isolated large (up to 72 mm in length) seeds from the upper Tambak Member, along with 43 fossil leaves and two palynological samples from the lower Tambak Member. Pivotal results. We describe the extinct legume Jantungspermum gunnellii gen. et sp. nov. The J. gunnellii seeds are flattened on one side, bilobed, and heart shaped with a long hilum (~60 mm) overlain on the suture, closely resembling Castanospermum, the Australian black bean tree. The leaves represent seven morphotypes, which include Fabaceae but are otherwise unidentifiable. One specimen preserves in situ cuticle. The palynoflora includes diverse ferns and palms, Typhaceae, Onagraceae, and forest taxa, including Podocarpaceae, Sapindaceae, and Fabaceae, indicating a largely freshwater coastal swamp environment in the lower Tambak Member. Conclusions. The Jantungspermum seeds are double the length of Castanospermum seeds, representing a closely related but extinct papilionoid taxon. The discovery suggests a Sundan precollision history, a much later SundaSahul migration, and an eventual Asian extinction for the Castanospermum lineage, which today inhabits coastal rainforests of northern Australasia. The seeds represent the only known fossil relative of Castanospermum, the oldest legume fossils from Malesia, and one of the largest fossil angiosperm seeds. The new seeds, leaves, and palynomorphs provide a window into Eocene Malesian vegetation and rare macrofossil evidence of Sundan history for a living Australasian lineage. © 2024 The University of Chicago.
Department of Geosciences and Earth and Environmental Systems Institute, Pennsylvania State University, University Park, 16802, PA, United States; Millennium Scholars Program, Pennsylvania State University, University Park, 16802, PA, United States; Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, T2L 2A7, AB, Canada; Biostratigraphic Associates, Staffordshire, Stoke-on-Trent, ST6 8NE, United Kingdom; Paleontology and Quaternary Geology Research Group, Department of Geology, Institut Teknologi Bandung, Bandung, 40132, Indonesia; Department of Geology, Institut Teknologi Sumatera, Lampung, 35365, Indonesia; Florida Museum of Natural History, University of Florida, Gainesville, 32611, FL, United States; Department of Anthropology and Museum of Natural History, University of Iowa, Iowa City, 52242, IA, United States
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