Years later, the paleontologist Lachlan Hart revealed what the fossil he saw when he was 12 years old

Palaeontologist Lachlan Hart has finally solved that decades-long mystery and formally described the prehistoric creature in the Journal of Vertebrate Paleontology. By chance, Hart first visited the fossil at the exhibition as a dinosaur-obsessed 12-year-old in 1997.

A spectacular fossil discovered by a retired chicken farmer has been identified by palaeontologists as a new type of Triassic amphibian that stalked the freshwater streams of the Sydney basin 240 million years ago. Arenaerpeton supinatus was discovered in rocks cut from a nearby quarry that were intended for the building of a garden wall.

Arenaerpeton looks a lot like the modern Chinese Giant Salamander. Photo: UNSW Sydney/Richard Freeman

 240-million-year-old fossil of an amphibian that was found in a retaining wall in the 1990s has been formally named and described by scientists at UNSW Sydney and the Australian Museum.

The fossil was originally found by a retired chicken farmer in rocks obtained from a local quarry intended for use in the construction of a garden retaining wall and was subsequently donated to the Australian Museum in Sydney.

An artist's impression of Arenaerpeton supinatus, the ancestor of today's Chinese Giant Salamander. Image: Jose Vitor Silva

Palaeontologist Lachlan Hart, who holds joint roles with UNSW Science and the Australian Museum, says the fossil – named Arenaerpeton supinatus, meaning ‘supine sand creeper’ – shows nearly the entire skeleton, and remarkably, the outlines of its skin.

“This fossil is a unique example of a group of extinct animals known as temnospondyls, which lived before and during the time of the dinosaurs,” says Mr Hart, a PhD candidate in the School of Biological, Earth and Environmental Sciences (BEES) at UNSW.

“We don’t often find skeletons with the head and body still attached, and the soft tissue preservation is an even rarer occurrence.”

Arenaerpeton inhabited freshwater rivers in what is now known as the Sydney Basin during the Triassic period, 240 million years ago. Mr Hart says it most likely hunted other ancient fish such as Cleithrolepis, but apart from that, there is not much evidence that tells us about the other animals that Arenaerpeton shared the land and waters with.

“Superficially, Arenaerpeton looks a lot like the modern Chinese Giant Salamander, especially in the shape of its head,” Mr Hart says.

“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.”

The Arenaerpeton supinatus fossil on a pallet
Arenaerpeton looks a lot like the modern Chinese Giant Salamander. Photo: UNSW Sydney/Richard Freeman

Lachlan Hart says the fossil is a unique example of a group of extinct animals known as temnospondyls, which lived before and during the time of the dinosaurs. Photo: UNSW Sydney/Richard Freeman

Lachlan Hart (centre left) with his family at the Darling Harbour exhibition in 1997.

Mr Hart says what is exciting about the discovery is that Arenaerpeton is large – estimated to be about 1.2m from head to tail – when most other closely related animals that lived at the same time were small.

“The last of the temnospondyls were in Australia 120 million years after Arenaerpeton, and some grew to massive sizes. The fossil record of temnospondyls spans across two mass extinction events, so perhaps this evolution of increased size aided in their longevity.”

Dr Matthew McCurry, Senior Lecturer in UNSW’s School of BEES and Curator of Palaeontology at the Australian Museum says the fossil is a significant find in Australian paleo history.

“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,” says Dr McCurry, who is also a co-author on the study. “It represents a key part of Australia’s fossil heritage.”

The study has been published in the Journal of Vertebrate Paleontology, and the fossil will be on display at the Australian Museum, Sydney, later this year.

sourche: unsw.edu.au