Several 250-million-year-old specimens from museum collections in Australia and the United States have revealed a surprising diversity of trematosaurid temnospondyls in Western Australia, showing that early marine amphibians spread across continents soon after the end-Permian mass extinction.
The ancient marine amphibians Erythrobatrachus (foreground) and Aphaneramma (background) swimming along the coast of what is now far norther Western Australia 250 million years ago. Image credit: Pollyanna von Knorring, Swedish Museum of Natural History.
“The cataclysmic end-Permian mass extinction and extreme global warming prompted the emergence of modern marine ecosystems at the beginning of the Age of Dinosaurs (Mesozoic Era), some 252 million years ago,” Dr. Benjamin Kear from the Swedish Museum of Natural History and his colleagues said in a statement.
“This landmark evolutionary event involved the earliest appearances of sea-going tetrapods (limbed vertebrates), including both amphibians and reptiles, which quickly rose to dominance as aquatic apex-predators.”
“To date, the fossils of these earliest sea monsters have been largely documented from the northern hemisphere.”
“By comparison, southern hemisphere records are geographically sparse and incompletely known.”
In their new study, the paleontologists analyzed the fossils of marine amphibians from the iconic Kimberly region of far northern Western Australia.
“These fossils were initially discovered in Australia during scientific expeditions undertaken in the early 1960s and 1970s,” the researchers said.
“The recovered specimens were distributed between museum collections in Australia and the United States.”
“The resulting research was finally published in 1972, and identified a single species of marine amphibian, Erythrobatrachus noonkanbahensis, named from several skull fragments found weathering out of a rock outcrop on Noonkanbah cattle station east of the isolated Kimberly township of Derby.”
“Unfortunately, the original fossils of Erythrobatrachus were lost sometime during the intervening 50 years.”
“This launched a search through international museum collections, which culminated with the rediscovery and reassessment of these enigmatic ancient marine amphibian remains in 2024.”
According to the scientists, Erythrobatrachus was a trematosaurid temnospondyl.
“The trematosaurids were superficially ‘crocodile-like’ relatives of modern salamanders and frogs that grew up to 2 m (6.6 feet) in length,” they said.
“They are important because their fossils occur in rock deposits laid down as sediment in coastal settings from less than one million years after the end-Permian mass extinction.”
“They are, therefore, the geologically oldest currently recognizable group of Mesozoic marine tetrapods.”
Surprisingly, however, the detailed study showed that the skull fragments of Erythrobatrachus did not all belong to a single species.
Rather, they represented at least two distinct types of trematosaurids: Erythrobatrachus and another species attributable to the well-known genus Aphaneramma.
“Examination of the Erythrobatrachus skull using high-resolution 3D imaging suggests that it was about 40 cm (16 inches) long when complete, and came from a large-bodied, broader-headed top-predator,” the authors said.
“On the other hand, Aphaneramma was about the same size but had a long thin snout for catching small fish.”
“Both of these trematosaurids swam through the water column, but would have hunted different prey in the same habitat.”
“Furthermore, while Erythrobatrachus in known exclusively from Australia, fossils of Aphaneramma have been reported from similar aged deposits on Svalbard in the Scandinavian Arctic, the Far East, Pakistan and Madagascar.”
“The Australian trematosaurid remains thus show that these earliest Mesozoic marine tetrapods not only radiated rapidly into a range of ecological niches, but also managed to disperse worldwide, perhaps following the coastal margins of interconnected supercontinents during the first two million years of the Age of Dinosaurs.”
The team’s paper was published this month in the Journal of Vertebrate Paleontology.
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Benjamin P. Kear et al. Revision of the trematosaurid Erythrobatrachus noonkanbahensis confirms a cryptic marine temnospondyl community from the Lower Triassic of Western Australia. Journal of Vertebrate Paleontology, published online February 22, 2026; doi: 10.1080/02724634.2025.2601224