A creature frozen mid-existence, waiting in a quarry to be noticed
In the unhurried act of preparing a garden wall, a retired farmer in New South Wales unknowingly held 240 million years of Earth's history in his hands. The sandstone block he had ordered from a local quarry concealed the nearly complete remains of Arenaerpeton supinatus, a tusked, meter-long amphibian that once hunted in the freshwater rivers of ancient Gondwana. Formally named in 2023, the fossil is singular in its preservation of both skeleton and soft tissue — a rarity that speaks to the improbable conditions required for the deep past to reach us at all.
- A retired chicken farmer near Kincumber, Australia, flipped over a quarry stone and found the unmistakable outline of a spine and limbs pressed into the rock — a discovery that would take years to reach the scientists who could understand it.
- Arenaerpeton supinatus was no gentle creature: a chunky, 1.2-meter predator with roof-of-mouth tusks built for ambushing fish, it prowled Triassic freshwater rivers at a time when Australia was still locked into the Gondwana supercontinent.
- The fossil's survival defies the odds — sandstone environments are hostile to preservation, yet this specimen arrived nearly complete, fully articulated, and carrying traces of soft tissue, suggesting it sank into still, oxygen-starved water where decay could not reach it.
- Paleontologists at UNSW and the Australian Museum have called it one of the most significant New South Wales fossils in thirty years, filling a critical gap in the continent's prehistoric record.
- The find may help explain how temnospondyls — a lineage that outlasted two mass extinctions and persisted in Australia for another 120 million years — evolved toward ever-larger body sizes, with Arenaerpeton itself an early marker of that trend.
Mihail Mihailidis had ordered a sandstone block from a quarry near Kincumber, Australia, intending nothing more than a retaining wall. When he turned the stone over, he found something that stopped him: the clear impression of an ancient creature, its spine and limbs still legible in the rock after 240 million years.
The stone stayed with the Mihailidis family for some time before they donated it to the Australian Museum, where it waited in storage until 2023. That year, paleontologists formally identified and named it: Arenaerpeton supinatus, a temnospondyl amphibian from the Triassic period. Lachlan Hart of UNSW described it as superficially resembling a Chinese Giant Salamander in the head, but far bulkier and more dangerous — its most arresting features were a pair of fang-like tusks on the roof of its mouth, built for hunting fish. Without its tail, the fossil measured roughly 1.2 meters.
What elevates the discovery beyond its age is how it survived. Sandstone is an unlikely medium for preservation — its dynamic, oxygen-rich formation typically scatters and decomposes remains quickly. Yet Arenaerpeton's skeleton arrived nearly complete, fully articulated, and with traces of soft tissue intact. Hart believes the animal died in still water with low oxygen levels, slowing decay long enough for sediment to seal its form. It is the only known specimen of its species.
When this creature was alive, Australia was part of Gondwana and positioned far closer to the South Pole. The world was still recovering from the Great Dying, Earth's most catastrophic extinction event. Temnospondyls ranged widely across the supercontinent, and this individual inhabited what is now the Sydney Basin.
Matthew McCurry, also of UNSW and the Australian Museum, described it as among the most important New South Wales fossils recovered in three decades. Hart noted that temnospondyls endured in Australia for another 120 million years after Arenaerpeton's time, some growing to enormous sizes across two further extinction events. The fossil that was nearly mortared into a garden wall may yet help explain how they managed to last so long.
Mihail Mihailidis, a retired chicken farmer, was doing what seemed like ordinary work. He had ordered a block of sandstone from a local quarry near Kincumber, Australia, intending to use it as part of a retaining wall for his property. When he flipped the stone over to examine it more closely, he stopped. Pressed into the rock with unmistakable clarity was the outline of something ancient—a creature with a spine, limbs, and the proportions of something that had once swum through water.
The stone sat in the Mihailidis family's possession for years before they donated it to the Australian Museum. There it remained in storage until 2023, when paleontologists formally identified and named the creature: Arenaerpeton supinatus, a rare extinct amphibian that lived roughly 240 million years ago during the Triassic period. It belonged to a group called temnospondyls, distant relatives of modern amphibians, though this particular specimen bore little resemblance to anything alive today.
Lachlan Hart, a paleontologist at the University of New South Wales and the Australian Museum, described the animal as superficially similar to the Chinese Giant Salamander in head shape, but far bulkier and far more formidable. Its most striking features were its teeth—not just ordinary teeth, but a pair of fang-like tusks protruding from the roof of its mouth, the kind of weaponry suited to hunting fish in freshwater rivers. Without its tail, the fossil measured approximately 1.2 meters long, placing it toward the larger end of early temnospondyls in Australia, though some of its later relatives would eventually dwarf it.
What makes Arenaerpeton extraordinary is not merely what it was, but how it was preserved. Sandstone typically forms in dynamic, oxygen-rich environments where bodies decompose rapidly and scatter. Complete skeletons are vanishingly rare in sandstone deposits. Soft tissue—skin, muscle, body outlines—almost never survives the process. Yet Arenaerpeton's skeleton is nearly complete, fully articulated, and retains traces of soft tissue. It is the only specimen of its species ever discovered.
The fossil's exceptional preservation suggests that Arenaerpeton died in still water, likely in an environment where the bottom layers were either oxygen-poor or cold enough to discourage scavengers. With minimal disturbance and limited oxygen, decay slowed dramatically. The surrounding sediment had time to seal the animal's form before decomposition could obliterate it. Hart noted that finding skeletons with head and body still connected is uncommon; finding soft tissue preservation alongside it is rarer still.
When Arenaerpeton lived, Australia was part of the Gondwana supercontinent, positioned much closer to the South Pole than today. The world was still in the aftermath of the Great Dying, the most severe extinction event in Earth's history. Temnospondyls were distributed widely across Gondwana, their fossils scattered across continents that would later drift apart. This particular specimen inhabited the freshwater rivers of what is now the Sydney Basin.
Matthew McCurry, also of UNSW and the Australian Museum, called it one of the most significant fossils recovered in New South Wales in three decades. The discovery fills a gap in Australia's paleontological record and may illuminate how temnospondyls evolved. Hart observed that the last of these creatures persisted in Australia for another 120 million years after Arenaerpeton's time, and some grew to enormous sizes. The fossil record of temnospondyls spans two mass extinction events. Perhaps, Hart suggested, the evolutionary trend toward larger body size—a trend visible in Arenaerpeton's own substantial frame—contributed to the group's remarkable longevity.
The stone that Mihailidis selected for his garden wall never became part of a retaining structure. Instead, it became a window into a lost world, a creature frozen mid-existence that had waited in a quarry for someone to notice it was there.
Notable Quotes
This is one of the most important fossils found in New South Wales in the past 30 years, so it is exciting to formally describe it. It represents a key part of Australia's fossil heritage.— Matthew McCurry, paleontologist at UNSW and the Australian Museum
We don't often find skeletons with the head and body still attached, and the soft tissue preservation is an even rarer occurrence.— Lachlan Hart, paleontologist at UNSW and the Australian Museum
The Hearth Conversation Another angle on the story
What made this fossil so different from the thousands of other fossils that have been found in sandstone?
Sandstone is actually a hostile environment for preservation. It forms in places with moving water and oxygen, which breaks bodies apart. You usually get scattered bones or teeth at best. A complete skeleton with soft tissue intact is almost unheard of.
So how did Arenaerpeton escape that fate?
It died in the right kind of wrong place—still water, probably cold or oxygen-poor at the bottom. Scavengers couldn't reach it. Decay slowed to almost nothing. The sediment sealed it in before it could fall apart.
The farmer just found it by accident while building a wall?
Yes. He had no idea what he had. It sat in his family's possession for decades before they donated it. That's decades of not knowing you were holding one of the most important fossils found in New South Wales in 30 years.
What does this creature tell us about how life evolved after the Great Dying?
Arenaerpeton shows us what temnospondyls looked like in the early recovery. Its size—1.2 meters—is substantial for its time. Later relatives grew much larger. That size increase might have been the key to surviving two more mass extinctions.
So this one fossil could explain why an entire group of animals lasted so long?
It's a piece of the puzzle. We have the beginning and the end of the temnospondyl story in Australia, but very little in between. Arenaerpeton helps us see the trajectory.