Heavyset, gnarly and 240m years old: This amphibian fossil is finally named

9 Aug 2023

Lachlan Hart with the fossil Arenaerpeton supinatus. Image: Richard Freeman

Discovered by a farmer in the 1990s, the giant amphibian is related to salamanders and frogs but its large size and tusk-like fangs suggest that it lived a life more akin to crocodiles.

A new species of amphibian has been named and described nearly 30 years after its discovery in New South Wales, Australia.

The fossil is about 240m years old and comes from the Triassic period. It belongs to a group of extinct animals known as chigutisauridae, which are a family of brachyopoid temnospondyl amphibians that lived before and during the time of the dinosaurs.

The Australian chigutisaurid record is sparse so this rare and well-preserved discovery adds important information to the fossil record.

Named Arenaerpeton supinatus or ‘supine sand creeper’, the fossil was found in the mid-1990s by a retired chicken farmer in rock obtained from a local quarry.

The farmer donated the fossil to the Australian Museum in Sydney.

According to palaeontologist Lachlan Hart, “Superficially, Arenaerpeton looks a lot like the modern Chinese giant salamander, especially in the shape of its head”.

“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.”

Artist's impression of giant amphibian fossil swimming in water after a fish seen from below.

Reconstruction of Arenaerpeton supinatus, preying on Cleithrolepis granulata. Reconstruction by José Vitor Silva.

Hart is doing a PhD at the Australian Museum and in the School of Biological, Earth and Environmental Sciences at the University of New South Wales. He is the lead author on the paper, published in the Journal of Vertebrate Paleontology, which describes Arenaerpeton.

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

Arenaerpeton would have inhabited freshwater rivers in what is now known as the Sydney Basin. Hart says it most likely hunted other ancient fish such as Cleithrolepis. However, little is known about the other animals that would have shared the land and waters with the large amphibian.

It is estimated to be about 1.2 meters from head to tail making it much larger than other closely related animals alive at the same time.

“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 Dr Matthew McCurry, curator of palaeontology at the Australian Museum and co-author of the study. “It represents a key part of Australia’s fossil heritage.”

Arenaerpeton will go on display at the Australian Museum in Sydney later this year.

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Rebecca Graham is production editor at Silicon Republic