The fossil of a car sized mega-wombat has been unearthed in northern Australia, scientists said Wednesday -- the most complete skeleton of its kind.

Weighing in at a whopping three tonnes, the herbivorous diprotodon was the largest marsupial to ever roam the earth and lived between two million and 50,000 years ago.

A relative of the modern-day wombat, the diprotodon skeleton was dug up in remote Queensland last week -- the most northerly specimen ever discovered -- and scientists believe it could shed valuable light on the species' demise.

Along with Australia's other megafauna, which included towering kangaroos and gigantic crocodiles, diprotodon became extinct around the same time that indigenous tribes first appeared and debate has raged about the role of humans.

"There's been a lot of debate about what killed the megafauna and it's quite a hot topic in paleontology," Sue Hand, a professor on the team that made the discovery, told AFP.

Hand's fossil, the most complete diprotodon ever found in Australia, was well preserved and could be quite accurately dated, offering valuable insights into the role of humans and climate change in its demise, she said.

"Dating has been one of the bugbears of trying to unravel what happened," she said.

"It will be very interesting to see its age and if people came in first, for instance, from the north. There could be some very interesting data to be extracted from this find."

The animal was two metres tall (6 feet, six inches) and 3.5 metres (11 feet, six inches) long, and was the size of a rhinoceros or a car, pigeon-toed and with a backward-facing pouch, she said.

"They basically looked a lot like a wombat, a very big beefed-up wombat, much bigger than obviously anything that's around today," said Hand.

Megafauna are thought to have evolved to such large sizes to cope with inhospitable climates and food scarcity, with fossils found in Australia of prehistoric emus, tree-dwelling crocodiles and carnivorous kangaroos.