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Humans have long been blamed for hunting the American mastodon - an ancient relative of the elephant - to extinction.

But new radiocarbon dating of North American fossils suggests that the animals became extinct before humans colonised the region.

Experts are still not absolutely certain why the animals died out, but now think that changing habitats from forests to tundra could have played a role.

While it was traditionally thought that mastodons (illustrated) roamed areas in the Arctic and Subarctic when it was covered with ice caps, scientists now think that that the area was only temporarily home to the animals when the climate was warm. They also disappeared before humans colonised the region

It was popularly thought that mastodons lived in the Arctic and Subarctic when the area was covered by ice caps.

But, that view is at odds with what scientists currently know about the massive animals' preferred habitat of forests and wetlands abundant with leafy food.

To examine the mismatch, an international team of researchers carbon dated fossils and now believe that the Arctic and Subarctic were only temporary homes to mastodons when the climate was warm.

The new findings, published in the journal Proceedings of the National Academy of Sciences, indicate that mastodons suffered local extinction several tens of millennia before either human colonisation - the earliest estimate of which is between 13,000 and 14,000 years ago. 

New radiocarbon dating of North American mastodon fossils suggests that the animals became extinct before human colonisation of North America. The researchers dated a collection of 36 fossil teeth (pictured)

They also hint that the creatures died out before the onset of climate changes at the end of the ice age about 10,000 years ago, when they were among 70 species of mammals to disappear completely in North America.

Ross MacPhee, a curator in the Department of Mammalogy at the American Museum of Natural History, said: 'Scientists have been trying to piece together information on these extinctions for decades.

'Was it the result of over-hunting by early people in North America? Was it the rapid global warming at the end of the ice age?

'Did all of these big mammals go out in one dramatic die-off, or were they paced over time and due to a complex set of factors?'

Over the course of the late Pleistocene era, between about 10,000 and 125,000 years ago, the American mastodon (Mammut americanum) became widespread and occupied many parts of continental North America.

Grant Zazula, a palaeontologist in the Yukon Palaeontology Programme, said: 'Mastodon teeth were effective at stripping and crushing twigs, leaves, and stems from shrubs and trees.

'So it would seem unlikely that they were able to survive in the ice-covered regions of Alaska and Yukon during the last full-glacial period, as previous fossil dating has suggested.'

The researchers used two different types of precise radiocarbon dating on a collection of 36 fossil teeth and bones of American mastodons from Alaska and Yukon - the region known as eastern Beringia.

The dating methods, performed at Oxford University and the University of California, were designed to only target material from bone collagen. 

Over the course of the late Pleistocene era, between about 10,000 and 125,000 years ago, the American mastodon (Mammut americanum) which is shown in this illustration alongside other large furry beasts, became widespread, and occupied many parts of continental North America

All of the fossils were found to be older than previously thought, with most surpassing 50,000 years, which is the effective limit of radiocarbon dating.

When taking mastodon habitat preferences and other ecological and geological information into account, the experts believe that mastodons probably only lived in the Arctic and Subarctic for a limited time around 125,000 years ago, when forests and wetlands were established and the temperatures were as warm as they are today.

Mr Zazula added: 'The residency of mastodons in the north did not last long.

'The return to cold, dry glacial conditions along with the advance of continental glaciers around 75,000 years ago effectively wiped out their habitats.

'Mastodons disappeared from Beringia, and their populations became displaced to areas much farther to the south, where they ultimately suffered complete extinction about 10,000 years ago.'

The new report suggests that humans could not have been involved in the local extinction of mastodons in the north 75,000 years ago as they had not yet crossed the Bering Isthmus from Asia.

The researchers dated a collection of 36 fossil teeth and bones of American mastodons from Alaska and Yukon - the region known as eastern Beringia