Lost For 40 Years, Found In The Wrong Drawer: The Ancient Fossil That Rewrote Prehistory

Sometime in 1984, a crucial piece of Australia’s prehistoric past quietly disappeared. A fossil pulled from a remote stretch of northwestern Western Australia, the skull remnant of a crocodile-like amphibian that once hunted in ancient seas roughly 250 million years ago, was loaned out from the Western Australian Museum and never came back. For four decades, researchers trying to make sense of Australia’s earliest marine predators were working from plaster casts of a specimen no one could find.

Then scientists went looking. What they found, sitting in a tray at the University of California Museum of Paleontology, had been relabeled under an entirely different species name, hiding in plain sight. Its rediscovery, detailed in a new study published in the Journal of Vertebrate Paleontology, solved more than a museum mystery. It led researchers to conclude that what scientists had long believed was a single prehistoric species was actually a composite of two distinct animals, and that Australia’s ancient coastline was home to a more varied community of open-water hunters than anyone had realized.

The creatures in question are called trematosaurids, a group of large, semi-aquatic amphibians, not true salamanders in the modern sense, but distant relatives that prowled ancient waters long before anything resembling a modern frog or newt existed. With elongated, tapered, crocodile-like skulls and eyes positioned to scan open water, they were built for hunting. After the end-Permian mass extinction devastated marine life on Earth about 252 million years ago, trematosaurids were among the first large predators to bounce back and spread across the globe, showing up in fossil deposits from Madagascar to Greenland to Pakistan. Australia had its own version. Or so researchers thought.

Australia’s Most Important Ancient Marine Fossil Had Gone Missing

Australia’s trematosaurid, Erythrobatrachus noonkanbahensis, was formally described in 1972 from bone fragments recovered in the Blina Shale, a rock formation left behind by a shallow, brackish seaway that once divided what are now the Australian and Indian landmasses. The species had a single official reference specimen, the holotype, and that specimen vanished after an unofficial loan to paleontologist John W. Cosgriff in 1984, reportedly never returned.

Lead author Benjamin P. Kear of the Swedish Museum of Natural History and colleagues tracked it down. They eventually found it at the University of California Museum of Paleontology, cataloged under the name “cf. Tertrema sp.,” a completely different genus. The specimen was formally returned to the Western Australian Museum, and the team got to work. Worth noting: a second reference specimen from the original 1972 description, WAM 71.6.22, remains missing to this day and could not be examined for this study.

Using the recovered holotype alongside a high-definition plaster cast and a 3D surface scan, the researchers compared it against another fossil that had been grouped with it since 1972. The skull shapes told completely different stories. The holotype is broad, consistent with what had originally been described for E. noonkanbahensis. The second fossil is dramatically narrower, shaped more like a long, tapered wedge, and closely resembles a genus called Aphaneramma, whose relatives have been found in Norway, Pakistan, Madagascar, and Russia. The researchers provisionally refer it to cf. Aphaneramma sp., acknowledging that a formal new species designation may follow as more evidence emerges.

As the authors write, the two specimens “demonstrably differ in their discernible palatal dentition,” meaning the arrangement of teeth on the roof of the mouth, a difference significant enough to separate them into distinct animals. A taxonomic split had actually been floated back in 1965 but was then set aside when the original species description was published in 1972. This study revives and confirms it.

Piecing Together a Prehistoric Australian Sea

What did that ancient world look like? Parts of what is now the remote Kimberley region of Western Australia were submerged beneath a shallow, tidal seaway that ebbed and flowed between the ancient Australian and Indian continental masses. Ripple marks and thin sediment layering preserved in the rock suggest the water was shallow, perhaps only a few feet deep in places. Most of the fossils found there are worn and broken, likely carried short distances by water currents before settling on the seafloor.

It was a busy ecosystem. Alongside the trematosaurids lived lungfish, early ray-finned fish, coelacanths, and what may have been sharks. Other amphibians, more bottom-dwelling and freshwater-tolerant, appear in abundance elsewhere in the same rock formation. The marine hunters, by contrast, were rare and geographically concentrated within the Blina Shale, pointing to a world where different creatures occupied distinct pockets of a sea that was gradually shifting from salty to brackish to fresh.

That ancient sea now appears to have held at least two large open-water hunters where only one was previously known. One, E. noonkanbahensis, seems to have been an animal found only in Australia. The other looks closely related to a genus that spread across much of the ancient world, possibly by following the coastline of Pangea, the supercontinent that once connected nearly all of Earth’s landmasses, as a kind of intercontinental dispersal route.

What This Means for Australia’s Ancient Marine Record

Erythrobatrachus noonkanbahensis, now defined solely by its long-lost holotype, holds a notable place in prehistory: based on current evidence, it is the only Early Triassic marine trematosaurid currently known exclusively from Eastern Gondwana, the ancient southern supercontinent that eventually broke apart into Australia, Antarctica, Africa, South America, and the Indian subcontinent. It also ranks among the earliest known marine tetrapods from Australasia.

Pulling two physically different animals out from under one name sharpens that record rather than complicating it. It tells us that Australia’s ancient coastline, in the immediate aftermath of Earth’s worst mass extinction, was already populated by at least two large, specialized, open-water hunters inhabiting a shallow, gradually regressing sea.

Forty years in a mislabeled drawer, and the fossil still had something to say.

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