You don't see that every day.
(Hart et al., J. Vertebr. Paleontol., 2023)
It all started with a simple landscaping project.
Retired chicken farmer Mihail Mihailidis just wanted to build a retaining wall. He acquired a block of sandstone from a local quarry in Kincumber, Australia, and set to work preparing it for its new purpose.
When he turned the stone over, however, his plans fell apart.
There, clear as daylight, was an unmistakable impression of an ancient creature. The outline was so distinct that even a non-expert could tell it wasn't just an odd pattern in the rock. Something had been preserved there – something with a spine, limbs, and a body that had once moved through water.
(UNSW Sydney/Richard Freeman)
In 2023, decades after the Mihailidis family donated the stone to the Australian Museum, scientists formally described the beastie, named Arenaerpeton supinatus. It's a rare, extinct relative of modern amphibians, belonging to a group known as temnospondyls, and it lived hundreds of millions of years ago.
It's similar to a prehistoric salamander, but chunkier, and with a nastier set of teeth.
"Superficially, Arenaerpeton looks a lot like the modern Chinese Giant Salamander, especially in the shape of its head," said paleontologist Lachlan Hart of the University of New South Wales (UNSW) and the Australian Museum.
"However, from the size of the ribs and the soft tissue outline preserved on the fossil, we can see that it was considerably more heavyset than its living descendants. It also had some pretty gnarly teeth, including a pair of fang-like tusks on the roof of its mouth."
In 2023, decades after the Mihailidis family donated the stone to the Australian Museum, scientists formally described the beastie, named Arenaerpeton supinatus. It's a rare, extinct relative of modern amphibians, belonging to a group known as temnospondyls, and it lived hundreds of millions of years ago.
It's similar to a prehistoric salamander, but chunkier, and with a nastier set of teeth.
"Superficially, Arenaerpeton looks a lot like the modern Chinese Giant Salamander, especially in the shape of its head," said paleontologist Lachlan Hart of the University of New South Wales (UNSW) and the Australian Museum.
"However, from the size of the ribs and the soft tissue outline preserved on the fossil, we can see that it was considerably more heavyset than its living descendants. It also had some pretty gnarly teeth, including a pair of fang-like tusks on the roof of its mouth."
(Jose Vitor Silva)
The fossil truly is a spectacular specimen. It's preserved in sandstone, which is interesting enough.
Sandstone often preserves ancient traces, but it typically forms in dynamic, oxygen-rich environments where bodies are easily broken apart and decompose quickly.
In most cases, that means only fragments, such as isolated bones, teeth, or tracks, survive long enough to fossilize. Complete skeletons are much harder to come by, and delicate features like skin or body outlines almost never make it through the process intact.
Arenaerpeton – the only specimen of its species ever found – is very far from the typical sandstone fossil. The skeleton is almost complete and fully articulated, and the fossil retains traces of soft tissue – rare in any fossil, let alone sandstone.
The fossil truly is a spectacular specimen. It's preserved in sandstone, which is interesting enough.
Sandstone often preserves ancient traces, but it typically forms in dynamic, oxygen-rich environments where bodies are easily broken apart and decompose quickly.
In most cases, that means only fragments, such as isolated bones, teeth, or tracks, survive long enough to fossilize. Complete skeletons are much harder to come by, and delicate features like skin or body outlines almost never make it through the process intact.
Arenaerpeton – the only specimen of its species ever found – is very far from the typical sandstone fossil. The skeleton is almost complete and fully articulated, and the fossil retains traces of soft tissue – rare in any fossil, let alone sandstone.
(Hart et al., J. Vertebr. Paleontol., 2023)
"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," said paleontologist Matthew McCurry of UNSW and the Australian Museum.
"It represents a key part of Australia's fossil heritage."
The researchers believe that Arenaerpeton died in a calm aquatic environment with anoxic or colder bottom waters, inhospitable to scavengers, where its carcass could lie undisturbed while fossilization processes unfolded.
With little disruption and limited oxygen, decay slowed to a crawl, giving the surrounding sediment time to seal in the shape of the animal's body before it could disintegrate.
"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," said paleontologist Matthew McCurry of UNSW and the Australian Museum.
"It represents a key part of Australia's fossil heritage."
The researchers believe that Arenaerpeton died in a calm aquatic environment with anoxic or colder bottom waters, inhospitable to scavengers, where its carcass could lie undisturbed while fossilization processes unfolded.
With little disruption and limited oxygen, decay slowed to a crawl, giving the surrounding sediment time to seal in the shape of the animal's body before it could disintegrate.
(Hart et al., J. Vertebr. Paleontol., 2023)
"We don't often find skeletons with the head and body still attached," Hart said, "and the soft tissue preservation is an even rarer occurrence."
The animal dates back around 240 million years, to the Triassic period – a time before dinosaurs rose to dominance, when the world was still recovering from the Great Dying, the most devastating extinction event the world has ever seen.
During this time, Australia was still part of the Gondwana supercontinent and sat closer to the South Pole than it does today. Temnospondyls were relatively widespread across Gondwana, and their remains have been found across multiple continents that later split apart.
Arenaerpeton inhabited freshwater rivers in a region now known as the Sydney Basin and likely hunted fish with its fearsome tusks.
The specimen is missing its tail, but Hart estimates its full length was around 1.2 meters (3.9 feet). That's toward the larger end for early temnospondyls in Australia, although some later relatives would grow significantly bigger.
This size could have given it a leg up the evolutionary ladder.
"The last of the temnospondyls were in Australia 120 million years after Arenaerpeton, and some grew to massive sizes," Hart explained.
"The fossil record of temnospondyls spans across two mass extinction events, so perhaps this evolution of increased size aided in their longevity."
Arenaerpeton spent decades languishing in storage before arriving at its rightful place in the fossil record – a missing link that may help explain the rise of the temnospondyls.
So maybe take a leaf out of Mihailidis's book and give a closer look to that slab of rock before adding it to your garden wall.
"We don't often find skeletons with the head and body still attached," Hart said, "and the soft tissue preservation is an even rarer occurrence."
The animal dates back around 240 million years, to the Triassic period – a time before dinosaurs rose to dominance, when the world was still recovering from the Great Dying, the most devastating extinction event the world has ever seen.
During this time, Australia was still part of the Gondwana supercontinent and sat closer to the South Pole than it does today. Temnospondyls were relatively widespread across Gondwana, and their remains have been found across multiple continents that later split apart.
Arenaerpeton inhabited freshwater rivers in a region now known as the Sydney Basin and likely hunted fish with its fearsome tusks.
The specimen is missing its tail, but Hart estimates its full length was around 1.2 meters (3.9 feet). That's toward the larger end for early temnospondyls in Australia, although some later relatives would grow significantly bigger.
This size could have given it a leg up the evolutionary ladder.
"The last of the temnospondyls were in Australia 120 million years after Arenaerpeton, and some grew to massive sizes," Hart explained.
"The fossil record of temnospondyls spans across two mass extinction events, so perhaps this evolution of increased size aided in their longevity."
Arenaerpeton spent decades languishing in storage before arriving at its rightful place in the fossil record – a missing link that may help explain the rise of the temnospondyls.
So maybe take a leaf out of Mihailidis's book and give a closer look to that slab of rock before adding it to your garden wall.
The Life of Earth
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