Hidden in the depths of rural Queensland is a fossil deposit so amazing that Sir David Attenborough regards it as one of the most important palaeontological sites in the world.

Near the Gregory River in north-west Queensland, Boodjamulla National Park, more commonly known as Lawn Hill, has been World Heritage listed for a quarter of a century.

And now there is new evidence that the fossil site may be surrounded by thousands more just like it.

One scientist has devoted his life to the region, uncovering deposits there since the 1970s.

Professor Michael Archer, co-leader of the long-running study, said Riversleigh was "globally unique" for its soft tissue, muscle and organ deposits that contain single cells.

"Even more incredibly and globally unique, in the cells we're finding that organelles like the nuclei are fossilised after 17 million years," he said.

A global project

These snake vertebrae found at Riversleigh are 19 million years old. ( Supplied: A Gillespie )

Palaeontologists at the site have been fascinated by its array of unique megafauna dating from up to 25 million years ago, a time when the now-desert environment was lush rainforest.

Serious exploration of Riversleigh began in 1976 and is still led by a core group of experts predominantly from the University of New South Wales.

"We now have more than 100 people working with us on these deposits spread across more than 26 institutions in more than 11 countries," Professor Archer said.

The professor was head of mammals at Queensland Museum in 1975 when his director at the time, Dr Alan Bartholomai, mentioned that he had seen a tooth sticking out of a rock at Riversleigh.

"That nearly caused me to drop my teacup, because I didn't know there was anything new at Riversleigh and I was very curious to know why it wasn't back at the museum with him," he said.

Hard limestone deposits might be difficult to crack open, but they preserve wildlife deposits in exquisite detail.

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

Palaeontologists continued to make regular visits to uncover more species and finish the pages of Riversleigh's book.

"And now we've had a big leap that suggests actually it's not a book, it's a library," Professor Archer said.

New Riversleigh

Professor Archer said a PhD student had recognised there was far more to this story than what was in Riversleigh World Heritage Area, which is colloquially known as D-site.

"He was interested in the wavelengths and what data you can get from satellites, broadly called remote sensing," he said.

It took a few months until the student came back with satellite data that depicted spots which they knew indicated fossil deposits.

This fossilised sabre-toothed bandicoot skull was found at Riversleigh. ( Supplied: Jon Woodhead )

Yet more than 10 kilometres beyond the site, there was a bigger area giving the same promising signals.

Professor Archer calls it New Riversleigh, but said there could be many more sites.

"I would think there are thousands more fossil sites to be discovered, and in those sites will be continually discovered new kinds of animals."

Animals like the desert sloth, described so eloquently by Attenborough in his letter.