Archaeologists with the Australian National University (ANU) have discovered fossils of seven giant rat species on East Timor in Southeast Asia, with the largest up to 10 times the size of modern rats.

Lead researcher Julien Louys from ANU said these are the largest-known rats to have existed.

"They are what you would call mega-fauna. The biggest one is about five kilos, the size of a small dog," said Louys. Just to put that in perspective, a large modern rat would be about half a kilo.

The work is part of the "From Sunda to Sahul" project, which is looking at the earliest human movement through Southeast Asia.

Researchers are now trying to work out exactly what caused the rats to die out. Louys said the earliest records of humans on East Timor date around 46,000 years ago, and they lived with the rats for thousands of years.

"We know they are eating the giant rats because we have found bones with cut and burn marks," he said.

"The funny thing is they were coexisting till about a thousand years ago. The reason we think they became extinct is because that was when metal tools started to be introduced in Timor; people could start to clear forests at a much larger scale," explained Louys.

He said the project team is hoping to get an idea of when humans first moved through the islands of Southeast Asia, how they were doing it and what impact they had on the ecosystem.

"We're trying to find the earliest human records as well as what was there before the humans arrived," said Louys.