By Paul Rincon
Science reporter, BBC News
The Bradshaw rock art is sophisticated for its age
An ancient cave painting from northern Australia depicts a previously unknown species of large bat, researchers say.
The team thinks the rock art from Australia's Kimberley region could date to the height of the last Ice Age - about 20-25,000 years ago.
The painting depicts eight roosting fruit bats - also called flying foxes.
They have features that do not match any Australian bats alive today, suggesting the art depicts a species that is now extinct.
The findings have been published online in the scholarly journal Antiquity.
The bats would not have lived in the same cave as the painting; they are depicted hanging on a vine, which indicates a lowland forest habitat.
Jack Pettigrew, from the University of Queensland, and colleagues report that the eight bats in the painting have white markings on their faces.
No present day Australian flying foxes possess these features.
Dr Pettigrew and his team then considered whether the bat matched any living "megabats" from other parts of the world.
Worldwide there are six such species, two in Africa and four living in islands off South-East Asia.
The two African species have irregular white markings, unlike the depiction.
One of the Asian species has a white patch above the eyes - which is inconsistent with the rock art; the other lacks the pale belly shown in the Kimberley painting.
This left Styloctenium wallacei, from the island of Sulawesi, Stylocteniummindorensis from Mindoro in the Philippines.
Styloctenium mindorensis resembles the Australian bats
All are medium-sized with the distinctive white facial stripe shown in the cave art. All are fruit eaters living in lowland forest. Although Styloctenium have small white markings just above the eyes, these would not have been visible in profile, say the researchers.
On balance, say the researchers, Styloctenium is the closest living genus to the ancient species in the painting.
No fossil bats that could fit the bill are known from the local area.
"Fossilisation is notoriously poor in the rocky tropical environment of the Kimberley," Dr Pettigrew told BBC News.
Small fossil bats are known from Queensland's Riversleigh rocks, from which they can be extracted using acetic acid. But no flying fox remains have been found. The Queensland fossils are 30 million years older than the Kimberley flying fox.
The bat depictions were found on a sandstone wall protected by overhangs, near Kalumburu. They belong to a type of rock art known as "Bradshaw".
This Bradshaw rock art was painted more than 17,500 years ago by sophisticated artists. The style is spread over an area belonging to several Aboriginal nations, each of which has a different name for the rock art.
"The art site has been chosen so that it is not exposed to sun, has a flat wall for the art and a cap to protect the wall from the weather," Dr Pettigrew said.
There is considerable debate about whether past mammal extinctions in Australia were caused by human hunting pressure or by climate change.
The researchers regard bats as too mobile to have been hunted to extinction by the culture that produced the cave art.
The demise of the Kimberley white-faced megabats is more likely to have resulted from the climatic and ecological changes that followed the end of the Ice Age, say the scientists.