I live in New York, so I've seen some big rats. But even the ones that gorge themselves on pizza max out at about two pounds. Now researchers have discovered fossils from rat ancestors that grew to be as big as 11 pounds -- the size of a small dog.

[Giant, ancient rodents may have used their teeth like an elephant’s tusks]

The researchers, who presented their findings this week at the Meetings of the Society of Vertebrate Palaeontology in Texas, identified the fossil remains of four new genera of murids -- the group that includes rats, mice, and gerbils -- from the Indonesian island of Timor.

They've distinguished at least eight distinct species of rodent, and they're all giant by today's standards. They're also the oldest ever found on Timor, dating back about 44,000 years.

According to archeological evidence from the area, humans (who were present in Timor starting at least 46,000 years ago) regularly hunted and butchered these megafauna.


Julien Louys holds the jaw bone of a giant rat species discocvered on East Timor, up against a comparison with the same bone of a modern rat. (Stuart Hay, ANU)

"We know they're eating the giant rats because we have found bones with cut and burn marks," researcher Julien Louys of the Australian National University said in a statement.

[Mice sing just like birds, but we can’t hear them]

But the giant rats didn't die out because humans loved roasting them. It seems likely that the last "giant" rats on the island only went extinct about 1,000 years ago. Louys and his fellow researchers blame this delayed extinction on the invention of metal tools, which allowed humans to clear forests more efficiently. That habitat destruction did in rats that survived competition with smaller relatives, predators like monitor lizards and large birds, and human hunting. 

They're not alone: Only two species of mammals native to Timor survived that period.

Louys and his colleagues wish to study how human migration changed the ecosystem of Timor. Their latest findings on rats, they write, suggest that the protection of forests may have been all that was needed to ensure happy cohabitation between humans and large murids.

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