The bizarre marsupial moles that eke out an existence in Australia's deserts evolved their odd physical traits in the damp soils of prehistoric rainforests, scientists now believe.
Blind, earless and covered in golden fur, today's marsupial moles spend most of their time burrowing through sandy desert soils, only occasionally breaching the surface.
Although they are related to other marsupials such as kangaroos and koalas, they look very similar to Cape golden moles, mammals that live in the desert sands of Africa.
Until now, scientists had assumed that marsupial moles evolved to adapt to the desert conditions they currently live in.
But a 20 million-year-old fossil discovered at the famed Riversleigh World Heritage fossil site in North-West Queensland has turned that thinking on its head.
The find is published today in the journal Proceedings of the Royal Society B.
Surprising evolutionary path
A team led by Professor Michael Archer from the University of New South Wales unearthed the fossil in deposits laid down at a time when the Riversleigh area was very wet and covered by rainforest.
The fossils suggest that marsupial moles became mole-like while burrowing through the mossy floors of those ancient forests.
"We were very surprised," says co-author Suzanne Hand, also from UNSW. "It was one of the last things we expected to find in deposits from that time."
The fossil remains are not identical to modern day marsupial moles. The researchers say they represent a transitional stage, documenting a period when the ancestors of today's moles were acquiring several of their current specialisations.
"They are well on the way to being a marsupial mole as we know them," says Hand. "Although in some aspects they are not as well adapted as the ones today."
The find suggests that although marsupial moles and their African counterparts look almost identical today, they took very different evolutionary pathways to reach the same point.
"This is a real text-book case of convergent evolution," says Hand. The fossil has been named Naraboryctes philcreaseri.