A fossil lizard discovered by researchers at Flinders University and a member of Western Australian Museum staff has been described as by far the largest and most bizarre skink that ever lived.

Related to the Shinglebacks – commonly known as sleepy lizards or bobtails – found in gardens today, Tiliqua frangens or 'Frangens’, was covered in thick spiny armour and measured roughly the size of a human arm.

The lizard lived during the Pleistocene, – roughly 2 million years ago, until going extinct 47,000 years ago – alongside famous megafauna such as marsupial lions, diprotodons and short-faced kangaroos.

WA Museum Technical Officer Terrestrial Vertebrates Dr Kailah Thorn, who studied the fossils as part of her PhD at Flinders University said Frangens had a unique chunky, spiked profile.

"Frangens was 1000 times bigger than the Australian common garden skink and reveals that even small creatures were supersized during the Pleistocene,” she said.

"Deciphering how Pleistocene animals adapted, migrated, or what eventually caused their extinctions might help us conserve today’s fauna, which faces pressures such as changing climate and habitat destruction.”

The creature was pieced together with bones unearthed from ongoing excavations at Wellington Caves in New South Wales and from fossils already held in museums around Australia.

Flinders University Palaeontologist and research co-author Dr Diana Fusco said during one of the digs at Wellington Caves the team new they had found something interesting.

“We started finding these spiked armoured plates that that had surprisingly never been recorded before. We knew we had something interesting and unique,” she said.

Research co-author, evolutionary biologist at Flinders University and South Australian Museum Professor Michael Lee said the extinction of Frangens coincides with the disappearance of megafauna and suggests these end-Pleistocene extinctions were more extensive, affecting smaller creatures.

"These large, slow armoured lizards might have filled the ecological niche of small land tortoises, absent from modern Australia," he said.

The new study, titled A giant armoured skink from Australia expands lizard morphospace and the scope of the Pleistocene extinctions, was published in Proceedings of the Royal Society of London B: Biological Sciences (14 June 2023).