Camels might be known as ships of the desert but they had giant ancestors that once roamed the Arctic.
Bone fragments belonging to a camel almost a third larger than any now living have been recovered from a remote site in the far north of Canada.
The animal lived 3.5 million years ago, when the High Arctic was warmer than it is today and covered in forest.
Scientists believe camels might have originated in North America before migrating across Asia via a land bridge between Alaska and Russia.
Today they still bear features that could have evolved to cope with harsh polar winters. Among these are the famous hump - used to store energy in the form of fat - wide flat feet that perform equally well on sand or snow, and large eyes for peering through the Arctic winter gloom.
Bones of another giant camel dating back around two million years were previously found 1,200 kilometres south in the Yukon.
The new camel, as yet unnamed, may be a close relative of this animal, thought to belong to the family Paracamelus from which all modern camels are descended.
Fossil fragments from a lower leg bone were collected from Ellesmere Island, deep within the Arctic Circle off the northern coast of Greenland.
Scientists at the University of Manchester used a pioneering molecular fingerprinting technique to test tiny samples of preserved connective tissue extracted from the bones.
The collagen was compared with that of the Yukon camel and 37 modern mammal species.
The findings, published in the journal Nature Communications, show an almost identical match to the modern day one-humped camel, the dromedary, as well as the Yukon camel.
Anatomical data, combined with the collagen information, suggested that the leg bone was roughly 30% larger than the same bone in a modern camel species.
Dr Natalia Rybczynski, from the Canadian Museum of Nature, who led the expedition that found the fossils, said: "The first time I picked up a piece, I thought that it might be wood. It was only back at the field camp that I was able to ascertain it was not only bone, but also from a fossil mammal larger than anything we had seen so far from the deposits."
She added: "We now have a new fossil record to better understand camel evolution, since our research shows that the Paracamelus lineage inhabited northern North America for millions of years, and the simplest explanation for this pattern would be that Paracamelus originated there. So perhaps some specialisations seen in modern camels, such as their wide flat feet, large eyes and humps for fat may be adaptations derived from living in a polar environment."
During the mid-Pliocene epoch, when the camel was alive, the Earth was around 2C to 3C warmer than it is today, and the Arctic may have been up to 22C warmer.
However, it would still have been a frigid environment. Average annual temperatures would have been slightly below freezing, and the long winters much colder.
Writing in the journal, the scientists said fat deposits - as seen in camels' humps - could have been "critically important for allowing populations to survive and reproduce in harsh climates characterised by six-month long, cold winters".
Dr Mike Buckley, from the University of Manchester's Institute of Biotechnology, said: "This is the first time that collagen has been extracted and used to identify a species from such ancient bone fragments.
"The fact the protein was able to survive for three and a half million years is due to the frozen nature of the Arctic. This has been an exciting project to work on and unlocks the huge potential collagen fingerprinting has to better identify extinct species from our preciously finite supply of fossil material."