In a region of outback Queensland so harsh only the dead seem to survive, palaeontologists have discovered a sprawling new fossil site bursting with the bones of ancient mammals, including a likely new species of primitive marsupial.
''There are some animals here I've never seen before,'' said University of NSW professor Michael Archer.
The vast fossil deposit, located next to the Riversleigh World Heritage fossil site, was uncovered by a former student who, while studying the region with satellite images, noticed unusual patterns in the rocks.
Last month Fairfax Media accompanied a dig team to the remote location 200 kilometres north of Mount Isa, which is only accessible by helicopter, for their first major excavation.
Already one site revealed a treasure trove of animal bones, many yet to be identified, including a never before seen bat specimen, a couple of large wombat relatives called diprotodontids, small primitive marsupials and an ancient ring-tailed possum.
A team led by University of NSW palaeontologist Mike Archer investigate fossil deposits in and around the World Heritage listed-Riversleigh area. Photography by Tony Walters. Selected images available from www.fairfaxsyndication.com Follow us at twitter.com/photosSMH Photo: Tony Walters
''This place is bone city,'' said Professor Archer, who, after decades of fossil digs, admits he has become a discovery junkie.
He said one of the most intriguing features of the new specimens was that their teeth were worn. The well-used dentures were distinct from most animals previously discovered at Riversleigh, which lived between 24 million and 15 million years ago, and suggested these new creatures were younger and ate a diet containing dust and grit, a symptom of a drier environment, Professor Archer said.
While Riversleigh is unique for its almost continuous and detailed 25-million-year transcript of Australia's mammal groups - including the ancestors of koalas, kangaroos and wombats - there is a substantial gap in the record, between about 15 million and 5 million years ago.
At this time, a period known as the late Miocene, the rainforests that dominated northern Australia started to dry out.
''We know almost nothing about what happened in this area at that time,'' Professor Archer said.
While the team are yet to analyse their discoveries in the laboratory, a preliminary assessment suggests the animals exhumed from the new location roamed the landscape at this critical time.
With support from the National Geographic Society, a team of cavers and explorers located another eight sites containing bone deposits.
''This is such an important place to us,'' he said.
Palaeontologist Troy Myers said despite their small size, teeth could reveal a lot about their owner.
''And teeth are the hardest part of the body, so they're the most likely part to be preserved,'' he said.
But the fossils would likely have remained a secret were it not for a former University pf NSW student, Ned Stephenson, who used satellite images to view the original Riversleigh site.
As well as accurately locating the known fossil deposits in the Riversleigh area, he saw the same pattern stretched far beyond the world heritage boundary.
While the team are not sure of the exact source of the signal on the satellite images, they suspect it is related to the types of rocks, known as tertiary limestone, where Riversleigh fossils are typically located.
''It's a new potential way of locating fossils without having to wear your shoe leather out walking around on the hills,'' Professor Archer said.
Dr Myers and fossil preparator Anna Gillespie will now spend months preparing the team's 1.8 tonne of limestone rocks for more detailed analysis.
''This is just the beginning of new Riversleigh,'' Professor Archer said.