Paleontologists have unearthed three large (up to 7.2 cm in length) seeds and 43 fossil leaves of an ancient legume species in the Wahana Baratama coal mine near Satui, South Kalimantan, Indonesian Borneo.
Jantungspermum gunnellii. Image credit: Spagnuolo et al., doi: 10.1086/730538.
The newly-identified legume species lived in Southeast Asia between 40 and 34 million years ago (Eocene period).
Named Jantungspermum gunnellii, it closely resembles the living Australian black bean tree, Castanospermum.
“This tree is only found today in the coastal rainforests of northern Australia and neighboring islands,” said Penn State’s Professor Peter Wilf and his colleagues.
The paleontologists found three fossil seeds, 43 leaves and pollen samples of Jantungspermum gunnellii in the Tanjung Formation in South Kalimantan, Indonesian Borneo.
They also discovered diverse fossilized bird tracks, burrowing traces of marine invertebrates and fossil turtle remains.
“The seeds of Jantungspermum gunnellii are some of the largest in the fossil record, excluding coconuts and some other palms,” they said.
“They would have grown in a pod that most likely reached up to 1 m (3 feet) long, or the length of a baseball bat, and fit up to five seeds.”
“The fossils are also the oldest definite fossil legumes from the Malay Archipelago and the first fossil record anywhere of plants related to the black bean tree.”
The researchers suggest that the ancestors of the black bean tree migrated from Asia into Australia during the tectonic-plate collision that brought the landmasses together and allowed for an exchange of plants and animals between the continents.
“The collision of the Southeast Asian and Australian tectonic plates, which began about 20 million years ago and continues today, led to a large exchange of plant and animal species between the landmasses,” they said.
“The findings provide the first macrofossil evidence of a plant lineage moving from Asia into Australia after the Asia-Australia tectonic collision.”
“These fossil seeds suggest that the ancient relatives of Castanospermum migrated into Australia from Southeast Asia during the tectonic collision event and later went extinct in Asia,” said Penn State doctoral student Edward Spagnuolo.
“The suggestion is in opposition to most of the existing direct macrofossil evidence for plant migrations, which represents lineages that moved from Australia into Asia.”
The results appear in the International Journal of Plant Sciences.
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Edward J. Spagnuolo et al. 2024. Giant Seeds of an Extant Australasian Legume Lineage Discovered in Eocene Borneo (South Kalimantan, Indonesia). International Journal of Plant Sciences, in press; doi: 10.1086/730538
