About 250 million years ago, a region that is now a harsh desert in remote northwestern Australia lay along the edge of a shallow bay connected to a vast prehistoric ocean. Fossils collected there more than six decades ago and largely overlooked in museum collections are now reshaping scientists’ understanding of how land animals first returned to the sea and spread across the globe.
The end-Permian mass extinction, the most devastating die-off in Earth’s history, struck about 252 million years ago and was followed by extreme global warming. In its aftermath, modern-style marine ecosystems began to take shape at the start of the Age of Dinosaurs (or Mesozoic era). During this critical window, the earliest sea-going tetrapods (limbed vertebrates), including amphibians and reptiles, emerged and quickly became dominant aquatic apex predators. Most fossils of these early marine hunters have been found in the northern hemisphere. Comparable discoveries from the southern hemisphere have been rare and remain poorly documented.
Now, a fresh analysis of 250 million-year-old fossils from the Kimberly region of northern Western Australia reveals a surprisingly diverse group of marine amphibians with unexpected global connections across ancient oceans.
Lost Fossils Rediscovered After 50 Years
Marine amphibian fossils were first uncovered in Australia during expeditions in the 1960s and 1970s. The specimens were divided between museums in Australia and the U.S.A. Research published in 1972 concluded that the material represented a single species, Erythrobatrachus noonkanbahensis. The species was identified from several skull fragments eroding out of rock at Noonkanbah cattle station, east of the remote Kimberly town of Derby.
Over the following decades, the original Erythrobatrachus fossils were misplaced. Their disappearance triggered an international search through museum collections. In 2024, the long-lost specimens were finally located, allowing researchers to reexamine these puzzling marine amphibians with modern techniques.
Early Marine Amphibians After the Permian Extinction
Erythrobatrachus belonged to a group known as trematosaurid temnospondyls. These animals were ‘crocodile-like’ relatives of today’s salamanders and frogs and could reach lengths of up to 2 m. Trematosaurids are especially significant because their fossils appear in coastal rock deposits formed less than 1 million years after the end-Permian mass extinction. As a result, they represent the oldest clearly recognizable group of Mesozoic marine tetrapods.
A closer look at the rediscovered skull fragments revealed an important surprise. The bones once attributed to a single species actually came from at least two different trematosaurids: Erythrobatrachus and a second form belonging to the genus Aphaneramma.
High-resolution 3D scans of the Erythrobatrachus skull indicate it measured about 40 cm long when complete and belonged to a large-bodied predator with a broad head. Aphaneramma was similar in overall size but had a long, narrow snout suited for snapping up small fish. Both species swam through open water in the same environment, yet they likely targeted different prey.
Evidence of Rapid Global Spread
Erythrobatrachus is known only from Australia. In contrast, Aphaneramma fossils have been discovered in rocks of similar age in Svalbard in the Scandinavian Arctic, the Russian Far East, Pakistan, and Madagascar. These findings suggest that some of the earliest Mesozoic marine tetrapods expanded quickly into multiple ecological roles and spread widely across the planet. They may have traveled along the coastlines of interconnected supercontinents during the first two million years of the Age of Dinosaurs.
The study appears in the Journal of Vertebrate Paleontology. The rediscovered Erythrobatrachus fossils are now being returned to Australia. Additional amphibian fossils from the Age of Dinosaurs can be seen at the Swedish Museum of Natural History.
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