A team of researchers from the University of NSW was exploring the world heritage Riversleigh fossil field, in northwestern Queensland, when they chanced upon the 15 million-year-old cave.
Among the hundreds of beautifully preserved fossils found beneath the limestone cave floor were 26 skulls from the Nimbadon, a wombat-like marsupial and major herbivore group before kangaroos.
By comparing the intact skulls from varying stages of the marsupial's life - including as babies in the pouch - scientists were able to map the Nimbadon's life cycle from birth to death in a world-first study.
"We've got skulls representing pouch young all the way through to elderly adults, and that's a first," said Karen Black from UNSW's School of Biological, Earth and Environmental Studies.
"There is no other fossil deposit (in the world) that has that."
Dr Black said the marsupials played a significant ecological role in prehistoric Australia. Scientists have been exploring sites at Riversleigh for about 30 years but have never made such a ground-breaking discovery.
"It's not until we begin to crack these rocks open that you realise how many fossils are in there," Dr Black said.
With the unique sample of skulls and skeletons, scientists will use CT scans to conclude how marsupials' brains developed over time and how this affected their behaviour, functionality and evolution.
The discovery of so many Nimbadon alongside galloping kangaroos, a fox-sized thylacine and forest bats was "really unusual", Dr Black said. It indicated they were roaming in large numbers when they fell through the vertical cave to their deaths.
This mob behaviour suggests the lush, dense vegetation synonymous with early Australia had begun to clear. "The cave is 15 million years old and samples a period of time when Australia was changing from . . . a greenhouse phase to an icehouse phase," Dr Black said.
"That is particularly important. If we can get an understanding of what was going on at this cave then we would be able to . . . predict what's going to happen with climate change in the future with Australia's flora and fauna."
Another important question that remains, however, is how many more secrets remain unlocked at the site.
Source: The Australian