18 March, 2014 9:34AM AEDT

Ancient bilby secrets uncovered with discovery of 15 million year old fossil

Researchers are learning more about how the Australian bilby lived 15 million years ago following the discovery of three fossilised teeth in north west Queensland.

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An endangered marsupial, the bilby

Researchers believe bilbies gathered their food differently 15 million years ago to how they do today. (: Supplied: AWC)

Fossil bilby teeth discovered in the Riversleigh World Heritage site

One of the fossil bilby teeth discovered in the Riversleigh World Heritage site. (Contributed : Dr Kenny Travouillon)

The fossilised bilby teeth were found in the Riversleigh World Heritage site.

Dr Kenny Travouillon from the University of Queensland's School of Earth Sciences says the teeth reveal information about how bilbies lived millions of years ago.

"Riversleigh at the time was a rainforest and today bilbies don't live in rainforests, they live in deserts," he said.

"But what's particularly interesting is those teeth were un-worn, the teeth (had a) low crown, but today the bilby has high crowns.

"The reason for that is bilbies today, when they actually feed, they dig in the dirt to get insects and worms from the ground, and when they put the insects in their mouth, they actually ingest a lot of sand and the sand actually wears down the teeth.

"That tells us that the diet was very different, it wasn't digging in the dirt. It was probably just picking the fruits at level, or was eating fruits from bushes, maybe eating insects on leaves, it was not ingesting all the sand that a modern bilby does."

The three fossilised bilby teeth were found inside a slab of limestone that was extracted from the Riversleigh World Heritage site and transported to Sydney by a UNESCO team five years ago.

The limestone was dissolved in mild acid for several months, which finally exposed the fossilised teeth.

Researchers have studied the teeth to uncover information about the evolution of the bilby.

Dr Travouillon says even small pieces of fossil can answer big questions.

"It's a shame we couldn't have more and I wish in the future we'll go back to the site and get another block and there'll be a whole bilby in there but we have to work with what we've got.

"Often we have only bits and pieces and we have to try and work out what this tells us.

"I'm basically a very highly-specialised puzzled solver."

He says the Riversleigh World Heritage site is a particularly special place for ancient fossils.

"Everything that comes out of it is in such good condition. We've got lots of skulls of animals coming out of these sites and every skull actually tells (us) about the evolution of the marsupials," he said.

"Getting all these fossils from Riversleigh we can know how the kangaroos and the koalas of today actually evolved to be the way they look and live today.

"What we know from Riversleigh, there was actually all these other species that are not related to anything that's living, we are actually learning a lot. Australia actually had a whole variety of things that no longer exist."