Scientists name new species of giant amphibian found in retaining wall

9 August, 2023, Sydney: A 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 the Australian Museum and UNSW Sydney, and published in the Journal of Palaeontology.

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.

Palaeontologist Lachlan Hart, who holds joint roles with the Australian Museum and UNSW Science says the fossil – named Arenaepeton 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, who is conducting his PhD under Dr Matthew McCurry at the Australian Museum and 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 which shared the land and waters with Arenaepeton.

“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.”

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, Curator of Palaeontology at the Australian Museum and Senior Lecturer in UNSW’s School of BEES said 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.

Editor’s Note:

Photos and research paper available here

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