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Jantungspermum gunnellii, a giant fossil seed of the ancestor of Castanospermum from pre-Neogene

NEWS - Giant seed fossils from Borneo provide evidence of ancient plant migration from Asia to Australia. Fossils of an extinct legume have been found in Australia, suggesting that a tectonic plate collision between Asia and Australia millions of years ago led to an exchange of plants and animals, including the migration of the ancestor of the black bean from Asia to Australia.

Jantungspermum gunnellii, a giant fossil seed of the ancestor of Castanospermum from pre-Neogene 1

The fossil collection from southern Borneo includes three large beans, pollen samples, about 40 leaves and a variety of other fossils including bird tracks, marine invertebrates and turtle fossils.

A team of researchers from Pennsylvania State University, the University of Alberta, Biostratigraphic Associates in the United Kingdom, the Bandung Institute of Technology, the University of Florida and the University of Iowa collected the fossils in 2014 from coal seams.

The new report in the International Journal of Plant Sciences aims to fill a significant gap in the fossil record of plants from Southeast Asia and highlights the importance of understanding the dynamics of ecosystems shaped by geological processes.

The giant seed fossils are shedding new light on ancient plant migrations. The ancient bean fossil, the size of a modern lime, is one of the largest seeds ever found in the fossil record and could hold the key to understanding the evolution of the diverse tropical rainforests of Southeast Asia and Australia.

The seed fossils belong to a now-extinct Fabaceae plant that once lived in Southeast Asia. The plant is closely related to Castanospermum, a genus of black bean tree that is now found only in coastal rainforests in northern Australia and surrounding islands.

The fossils date back to the Eocene period, about 34 to 40 million years ago. The ancestors of Castanospermum migrated from Asia to Australia during a tectonic plate collision that united the two landmasses and allowed plants and animals to be exchanged between the two continents.

Jantungspermum gunnellii, a giant fossil seed of the ancestor of Castanospermum from pre-Neogene 2

The discovery provides the first microfossil evidence of plant migration from Asia to Australia after the plate collision, the oldest legume fossil ever found in the Indonesian archipelago and the world’s first fossil record of a plant related to the black bean tree.

“Ancient relatives of Castanospermum migrated to Australia from Southeast Asia during a tectonic collision, and then went extinct in Asia,” said Edward Spagnuolo of Pennsylvania State University.

The researchers suggest that it is important to understand the dynamics of ecosystems shaped by geological processes to gain broader context and evolutionary implications. The lack of direct evidence for plant migration from Asia to Australia is due to the lack of fossil records from the Philippines, Indonesia, Timor Leste, Papua New Guinea and Malaysia.

The fossils were scanned using CT scanning technology at Penn State to analyze the taxonomy. The researchers found characteristics that most closely resembled modern Castanospermum, despite the absence of earlier fossil representatives of the genus.

The fossil seeds are named Jantungspermum gunnellii, with the genus name referring to “jantung” meaning heart in Indonesian and “spermum” meaning seed in Latin. The species name honors the late Gregg Gunnell, a vertebrate paleontologist who led the field excavation.

Fabaceae is one of the most diverse families with about 20,000 species alive today and is an essential element of tropical ecosystems. The seeds are the only pre-Neogene fossils, from 2.6 to 23 million years ago, in the humid tropics of Southeast Asia.

The tropics are the most diverse biome on Earth, yet there has been little investigation of the fossil record into how tropical ecosystems evolved, especially in Asia, even as extinction risks are rapidly increasing due to deforestation. The studies highlight the region’s overlooked paleobotanical potential and the need for more fossil samples.

Original research

Edward J. Spagnuolo, Peter Wilf, John-Paul Zonneveld, David Shaw, Aswan, Yan Rizal, Yahdi Zaim, Jonathan I. Bloch, and Russell L. Ciochon (2024). Giant Seeds of an Extant Australasian Legume Lineage Discovered in Eocene Borneo (South Kalimantan, Indonesia). International Journal of Plant Sciences. DOI:10.1086/730538

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