• Swamp Skink (Lissolepis coventryi), which is probably the living lizard most similar to the new fossil. (Dr Mark Hutchinson, SA Museum / Flinders University)Source: Dr Mark Hutchinson, SA Museum / Flinders University
A 25-million-year-old skink named Mike - an ancestor of today's bluetongue lizards - has been found in central South Australia.
Rae Johnston

18 Feb 2021 - 12:03 AM  UPDATED 18 Feb 2021 - 12:03 AM

A remote expedition to the large inland salt lake - Lake Pinpa - back in 2017 has been responsible for finding the fossil ancestors of wombats, platypus, kangaroos and even the thylacine. Now it can add bluetongue lizard to the list. 

Named Mike, or Mikebulli, in honour of Flinders University lizard researcher Professor Mike Bull, the tiny skink is 25-million-years-old, making it the continent's oldest skink. 

Professor Bull passed away in 2016, but not before inspiring generations of reptile scientists.

"Our colleague Professor Bull's long-term ecological studies of sleepy lizards were a massive contribution to biology," said Professor Mike Lee from Flinders University.

"The fossil record is essentially data from a long-term natural ecological study, so it's fitting that this fossil lizard is named in honour of Mike."

Palaeontologists and volunteers from Flinders University and the South Australian Museum focused on parts on the lake, seven hours drive north of Adelaide, where other fossils were previously unearthed. The area was once lush and green and is considered the continent's unique fauna cradle, particularly for its reptile diversity.

Found nearby were the koala's ancestors, a predatory bird, and fragments of a thylacine. There were also remains of prehistoric fish, platypus, dolphins and crocodilians.

"It was 45°C in the shade that day and hard work digging through the clay, but it was definitely worth it once the tiniest of bone fragments turned out to be those of the oldest Australian skink," said palaeo-herpetologist Dr Kailah Thorn, who researched at Flinders University as part of her PhD.

Dr Thorn, who now works as a curator of the Edward de Courcy Clarke Earth Science Museum at the University of Western Australia, said fossil lizards are tiny, often too small to be identified on the spot.

"Lizard skulls are made of more than 20 individual bones that all disarticulate when they fossilise," said Dr Thorn.

How did the researchers discover tiny fossil lizards in an area the size of one million soccer fields? Patience. 

"These lizard fossils owe their discovery to the patient sorting of tiny bones," said Flinders University Associate Professor, Trevor Worthy, a vertebrate palaeontologist. 

"A teaspoon holds hundreds of tiny bones – all revealed in translucent splendour under a microscope."

"Once every 30 spoons something else is found among the fish – usually a tiny mammal tooth. But the 2017 discovery of the oldest skink was a golden moment for a paleontologist," said Worthy.

Once found, the researchers placed the fossil in the evolutionary tree of lizards. That's when they discovered Mike was an early member of the skink sub-family Egerniinae - sitting alongside bluetongues, shingle backs, land mullets and spiny-tailed skinks. 

And because he is the oldest fossil evidence of this group of lizards, Mike helps pinpoint the timing of the arrival of scincid lizards to the continent. 

Meet 'The Swamp King': The prehistoric giant croc who ruled south-east Queensland
Like a "crocodile on steroids", The Swamp King was so large he hunted megafauna.