A marsupial lion that, in its heyday, would have had some animals "shaking in their boots", has been confirmed as a new genus.

Key points: The new genus of marsupial lion was previously believed to be part of Priscileo roskellyae (Thylacoleonidae) but has been found to be a different supremely specialised carnivore

The new genus of marsupial lion was previously believed to be part of Priscileo roskellyae (Thylacoleonidae) but has been found to be a different supremely specialised carnivore All of Riversleigh's lions are characterised by the same impressive teeth capable of slicing straight through bones

All of Riversleigh's lions are characterised by the same impressive teeth capable of slicing straight through bones Researchers say climate variation in the fossil record at Riversleigh was "the best way to predict the future"

Lekaneleo, nicknamed Leo, was at home to Adels Grove and the Riversleigh World Heritage area, a short 23 million years ago.

The area is a significant fossil site, once visited by Sir David Attenborough.

The cat was about the size of today's domestic cats, and it was previously believed to be part of the Priscileo roskellyae (Thylacoleonidae) genus because of its teeth — with three premolars and four molars — and because of its relatively small size.

A research paper authored by University of New South Wales' Anna Gillespie, Michael Archer, and Suzanne Hand has detailed the reclassification which Dr Archer said was one of "the exciting ones".

He said the cat was part of a "strange" group of marsupials.

"This little guy that we're calling Lekaneleo roskellyae … was one of the tiniest marsupial lions we've ever seen. It was actually like a pussy cat in size," Dr Archer said.

"What we've progressively found at Riversleigh, where there's been an amazing window of understanding about the evolution of this very strange group of marsupials, is that they started out as really tiny animals, smaller than a pussy cat.

Sir David Attenborough visited the Riversleigh fossil site in 2001. ( Supplied: Henk Godthelp )

"In Australia, the marsupial lions were the supremely specialised carnivores throughout at least the last 30 million years of Australian history.

"And this guy, this new one, we've only just recognised is highly different than any of the other previous ones we've seen — that's why it's been described now as a new genus of marsupial lion."

Alongside the Lekaneleo, some of the other marsupial lions found at Riversleigh include the Microleo attenboroughi, named for Sir David, the Wakaleo schouteni which was about the size of a panther, and larger lions the Thylacoleonids.

What was Leo?

Dr Archer said all of Riversleigh's lions were characterised by the same impressive premolar.

Dr Anna Gillespie dissolving limestone filled with bones from Riversleigh. ( Supplied: Michael Archer )

"They had an extraordinary, elongated, bolt-cutting type of premolar," he said.

"This was the most extraordinary adaptation or evolution that a carnivorous mammal has ever developed anywhere in the world.

"It is capable of slicing straight through bones."

So although Leo may have been the size of your average domestic cat, it certainly was not about to snuggle up on the couch.

"I would think that many of the animals in the Riversleigh ancient rainforest would have been shaking in their little furry boots when they saw this animal come along," Dr Archer said.

"We don't have any living animals today to tell us what these animals may have been doing.

"These forests were ever so much more complex than anything you may see now in the wet tropics.

"It makes us understand that the total effect that has happened in Australia is a steady loss of the complexities that was normal in the forests in Australia."

What more can Riversleigh tell us?

Riversleigh is a world-renowned site, and one which Dr Archer has been working at for four decades.

Serious exploration of Riversleigh began in 1976 and continues to this day. ( Supplied )

He said nowhere in Australia today has the diversity approaching the level which existed in Australia at the same time Leo did.

"We see over time, as climates have changed, as the rainforests have retreated to the edges of the continent, the biodiversity of Australia has steadily shrunk," Dr Archer said.

He said looking at the past was the best way to predict the future, and Riversleigh was a great place to do that.

At one point in its history Riversleigh saw a two-degree temperature rise which resulted in 50 per cent of its species being lost.

But Dr Archer said when temperatures dropped again those numbers began to regenerate — but that was over a space of 300,000 to 400,000 years.

"There is a message here of course and it's that if we keep allowing the Earth's temperature to rise, we are going to see a massive loss of biodiversity," he said.

"When you think about what's in the wet tropics … and you subtract every second kind of animal in those forests, you begin to understand how significant those losses are going to be.

Dorothy Dunphy's illustration of one area of the Riversleigh World Heritage site as it may have looked 18 million years ago. ( Supplied: Michael Archer )

"That's what the fossil record enables us to do. We're not confined to just guessing what's likely to happen as global temperatures rise, we've actually got a fossil record at Riversleigh that tells us what happened when this happened before.

"In that particular case [about 15 million years ago] … we did watch massive losses of species. But then we did watch, over hundreds of thousands of years, the species' diversity pick up again when the global temperature started to drop."