Sydney, July 31 - A bizarre bat species that is as much at home walking four-legged on the ground as winging through the air has been traced back to an Australian ancestor 20 million years ago, with the same rare ability.

The discovery overturns a long-held view that the agile walking and climbing skills of the lesser short-tailed bat - Mystacina tuberculata - evolved in the absence of any ground-dwelling mammal competitors or predators.

'The lesser short-tailed bat seems to be the sole survivor of an ancient Australian lineage now found only in New Zealand,' says Suzanne Hand, a bat expert at the University of New South Wales, (UNSW), who led the international study.

'This study shows that, contrary to existing hypotheses, bats are not overwhelmingly absent from the ground because of competition from, or predation by, other mammals,' adds Hand.

Along with the American common vampire bat - Desmodus rotundus, this bat is one of only two of 1,100 bat species worldwide that has a true four-legged walking gait when manoeuvring on the ground.