A recent study published in the Journal of Vertebrate Paleontology has identified two distinct ancient amphibian species from re-examined fossil fragments, some of which were lost for over 50 years. The fossils, initially discovered in Western Australia, belong to temnospondyl amphibians, ancient vertebrates that inhabited a brackish environment approximately 250 to 252 million years ago. The research not only clarified the presence of Erythrobatrachus but also identified Aphaneramma, a genus with a global distribution, suggesting that these early Mesozoic marine tetrapods were more widespread than previously understood.
Context of Discovery: Ancient Western Australia
The Kimberley region of Western Australia, currently characterized by rugged ranges, was a shallow bay at the edge of a prehistoric ocean approximately 250 to 252 million years ago, during the Early Triassic period. This era marked the development of modern marine ecosystems following a mass extinction event, with early sea-going limbed vertebrates, known as tetrapods, emerging as significant predators.
The creatures identified in the study are temnospondyls, a diverse lineage of amphibians with a fossil record spanning 210 million years, recognized for their survival through two mass extinctions.
Initial Discovery and Decades-Long Loss
In the 1960s, fossils from these animals, collectively known as the Blina shale, were uncovered on Noonkanbah station. A 1972 paper described several tetrapod skull fragments found at a rocky outcrop, identifying a new species, Erythrobatrachus noonkanbahensis, from three skull pieces.
Following this identification, specimens were distributed to various museum collections in Australia and the United States, subsequently becoming lost for more than five decades.
A high-quality plaster cast of one piece was retained by the Western Australian Museum.
2024: Rediscovery and Advanced Analysis
An international search for the lost specimens concluded in 2024. One of the original Noonkanbah fragments was located, having been mislabeled and stored at a museum collection in Berkeley, California, US.
A team of researchers from the University of New England, WA Museum Boola Bardip, Curtin University, and the University of New South Wales then undertook a re-examination. Utilizing high-resolution 3D imaging, the team analyzed this recovered original fossil alongside the existing plaster cast.
Revealing Two Distinct Species
The re-examination revealed that the two available pieces belonged to two distinct temnospondyl species, rather than just one.
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Erythrobatrachus: One fossil retained the name Erythrobatrachus. This trematosaurid temnospondyl is described as a crocodile-like relative of modern salamanders and frogs, with an estimated total length of up to 2 meters. Its skull, approximately 40 centimeters long, featured a broader, more robust head, suggesting its role as a top predator in its environment. Erythrobatrachus has been found exclusively in Australia.
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Aphaneramma: The other fossil was reclassified as a species attributable to the genus Aphaneramma, a previously described temnospondyl. This species, also with a skull length of approximately 40 centimeters, possessed a long, thin snout, likely adapted for catching small fish. This difference in feeding strategy would have allowed both species to coexist in the same habitat by targeting different prey.
Both Erythrobatrachus and Aphaneramma belong to the Trematosauria family of temnospondyls, a group known for its tolerance of saltwater environments, a characteristic not common among modern amphibians.
Global Reach and Ecological Resilience
While Erythrobatrachus has only been found in Australia, Aphaneramma fossils of similar age to the Blina Shale have been reported from various global locations, including the Scandinavian Arctic (Svalbard), the Russian Far East, Pakistan, and Madagascar. The confirmation of Aphaneramma's presence in Australia indicates a worldwide dispersal of these animals during the earliest Mesozoic era.
Trematosaurs are notable for their presence in rocks dating less than one million years after the Permian mass extinction, the most catastrophic extinction event in Earth's history.
The new discoveries from the Noonkanbah fragments suggest that these early Mesozoic marine tetrapods were more widespread in prehistoric oceans than previously thought. This research highlights the adaptability of temnospondyls and their ability to utilize diverse ecological niches, surviving extreme global changes. The rediscovered Erythrobatrachus fossils are scheduled for repatriation to Australia.