But new evidence on dates suggests that man's impact on the environment and climate change may be to blame.

"This is really the first good set of dates and the largest dating review of megafauna in Australia since the debate began about 170 years ago," the National Museum of Australia's head of research and development, archaeologist Mike Smith, told Reuters.

"We are in the midst of a dating revolution in Australia but the mystery is not over yet," Smith says. "If it was going to be easy to solve we would have solved it by now."

Academic furore over this pre-history mystery flared up again with a new exhibition of lost kingdoms at the National Museum, coinciding with a ground-breaking scientific paper.

Researchers applied a state-of-the-art dating technique to find these huge animals which disappeared as long ago as 46,000 years.

If the dates are right, this questions earlier theories blaming the last ice age 21,000 years ago, or man hunting the animals to extinction after arriving about 60,000 years ago.

Smith says the new dates pointed to a third theory - the "slow burn" - in which the megafauna was gradually wiped out by man changing the landscape plus climate changes.

SIZE COUNTS

While academics are agreed that dinosaurs were probably wiped out after a huge meteorite hit the planet about 65 million years ago, causing catastrophic cooling and acid rain, the jury is still out on the fate of Australia's megafauna that followed.

The heyday of giant animals was the Pleistocene era, about 1.6 million to 40,000 years ago.

It was during this time, when the world cooled and dried, that plants adapted to better survive long dry spells and became less lush and nutritious.

Plant-eating animals became larger as they ate more to get the nutrition they needed - and predators in turn grew bigger to cope with their larger prey.

In Africa, these was the origins of the elephant, giraffe and hippopotamus - megafauna which thrived as humans and the animals evolved together.

North America became home to the woolly mammoth and sabre-toothed cats, which were wiped out when man arrived about 12,000 years ago. Here archaeologists have found evidence of kill sites with tools, arrows and skeletons buried together.

Australia, isolated from other continents for 45 million years, developed its own distinctive fauna, including monster kangaroos, huge lizards and marsupial lions - of which 86 percent or up to 55 species were believed to have been wiped out.

Those that vanished included the large short-faced kangaroo, the Procoptodon, which grew up to three metres (10-feet) tall and 300 kg (660 pounds) in weight, with its foot reduced to a single toe adapted to move quickly across dry, hard land.

The wombat-like Dipotrodon, the largest marsupial known, was nearly four metres (13-feet) long, 1.5 metres (five-feet) tall and weighed 1.5 tonnes.

Smith says archaeologists discovered the existence of these massive creatures that used to dominate the continent about 170 years ago and initially put their demise down to climate.

Palaeo-ecologist David Horton argues swings in the global climate, including the last ice age 21,000 years ago, created extreme, arid conditions, wiping out most of these creatures.

MAN BLAMED

But by the late 1960s another theory emerged.

Evidence pointed to increasingly early human settlement of the continent, turning the finger of blame to Australia's Aborigines, who first arrived from Asia at least 60,000 years ago.