Scientists identified a 240-million-year-old fossil of a giant lizard-like creature

Scientists name new species of giant amphibian found in retaining wall.

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In 1990, a retired chicken farmer found a fossil in rocks obtained from a local quarry intended for use in constructing a garden retaining wall. He then donated that rock to the Australian Museum in Sydney.

Detailed analysis performed by UNSW Sydney and the Australian Museum scientists suggests that the fossil is of an amphibian and almost 240-million-year-old. This fossil represents a distinct species of the extinct temnospondyls, which existed both before and during the time of the dinosaurs.

The fossil has been named Arenaerpeton supinatus, meaning ‘supine sand creeper.’ In the Sydney Basin of today, Arenaerpeton lived in freshwater rivers during the Triassic period, 240 million years ago.

Palaeontologist Lachlan Hart, who holds joint roles with UNSW Science and the Australian Museum, says, “We don’t often find skeletons with the head and body still attached, and the soft tissue preservation is an even rarer occurrence.”

“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.”

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

“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 fossil of the Arenaerpeton is large. It is estimated to be about 1.2m from head to tail. Other closely related animals that existed during that time were small.

Mr. Hart says, “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 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 describe it formally. It represents a key part of Australia’s fossil heritage.”

Journal Reference:

  1. Lachlan J. Hart, Bryan M. Gee, Patrick Smith, et al. A new chigutisaurid (Brachyopoidea, Temnospondyli) with soft tissue preservation from the Triassic Sydney Basin, New South Wales, Australia. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2023.2232829

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