Everyone knows the camel as the ship of the desert - but new research is pointing towards its ancient ancestors actually being far more used to the cold of the north Canadian forests and the fat in the hump was essential for surviving in such a harsh climate, as Matt Kwong reports
Think of camels, and the chances are that the image you conjure up is of magnificent, if surly, beasts trudging steadily across a sweltering desert dune. They are, in the minds of most people, inextricably connected with some of the hottest places on Earth.
But it was not always that way. Long before camels were ships of the desert, new evidence suggests they were cold-weather beasts that roamed the frozen wilds of northern Canada.
And that discovery has led scientists to a surprising new theory about where the camel got its hump.
Camels have long been known to have a history well outside their current range. The first evidence of camels outside of North America was linked to Spain from about seven million years ago. Other fossils suggest a presence in China about six million years ago, and in Africa about five million years ago.
But last week, details were published for the first time of camel fossils found on Ellesmere Island in the High Arctic, 1,200 kilometres north of the areas where the extinct Yukon giant camel, known as paracamelus, was once believed to roam.
"What our evidence suggests is, in fact, that paracamelus originally spanned North America and Eurasia," said Natalia Rybczynski, a paleobiologist at the Canadian Museum of Nature and one of the authors of the paper in the latest edition of Nature Communications.
"This find is so important because it completely changes the evolution of the form of paracamelus, which is what gave rise to the modern camel."
Camels originated in North America about 45 million years ago, during the mid-Eocene Period, but eventually crossed into Eurasia, Sibera and Africa across the Bering land bridge, which once connected Russia and North America.
When the Bering Strait opened up, about 5.5 million years ago, it separated the North American camel population from their "Old World" cousins.
Dr Rybczynski, who led several field expeditions to Ellesmere Island between 2006 and 2010 and helped design the research programme, said a paracamelus restricted to the northernmost parts of North America would most likely have been specialised to living in the boreal forests - the dark, coniferous forests that cover much of modern inland Canada.
The newly discovered polar camel is probably a remnant of the "Old World" population that persisted separately in North America.
"This is a completely new way of thinking about the traits we see today," she said.
It suggests a surprising possibility for the origin of the camel's hump, long thought to be an adaptation to the scarcity of water in its modern habitats.
Instead, the fat stored in paracamelus's hump may originally have helped the animals survive the long, harsh winters of northern Canada, just as the fat stored by modern moose and deer does.
"Having a hump specialised in storing fat would be a very useful trait in this kind of harsh, boreal forest environment," said Dr Rybczynski.
The wide, flat feet of modern camels, and their ability to see well in the dark could have also been adaptations to walking in soft snowy environments and foraging for food during long periods of polar night.
The evidence comes from about 30 fragments of leg bone of a camel from the Pliocene epoch - between 2.6 and 5.3 million years ago.
The Arctic cold meant the bones were exceptionally well preserved, according to John Gosse, a geologist at Dalhousie University in Halifax, Nova Scotia. That allowed scientists from Dalhousie and the University of Manchester in the UK to subject the fragments to collagen fingerprinting, which looks at the proteins in the bone.
They found similarities between the collagen in the fragments and that in the Yukon camel, and in modern dromedaries such as the one-humped Arabian camels found in the UAE.
The bones were thick, suggesting the ancient camel was about 30 per cent larger than modern camels, weighing up to 900 kilograms, with an average shoulder height of about 2.7 metres.
To determine the age of the camel bones, Dr Gosse and his team used a technique called terrestrial cosmogenic nuclide dating to work out how long the surrounding layers of sand had been buried - and therefore how long ago they were deposited.
"We're interested in learning about how old the camel was, and we do that by determining how long the sands - which were eroded from the mountains to the south and to the north that were despoting in this little basin - were buried," Dr Gosse said.
Layers of sand near the fossils were dated by comparing ratios of rare radioactive isotopes produced in minerals once exposed to cosmic rays to samples that were buried deeper and shielded from cosmic rays.
The fossils were found to be three and a half million years old - in line with previous evidence.
These ancient giants may even have had to cope with temperatures quite as cold as those on Ellesmere Island today.
Global average temperatures were about 2°C to 3°C warmer than they are today, and the local climate on Ellesmere Island was warmer still - perhaps 14°C to 22°C warmer than now, according to a paleoclimate reconstruction. Even so, average temperatures would have hovered near freezing.
As for what is next, Dr Rybczynski plans to compare the High Arctic paracamelus samples to evidence from Ice Age deposits from Yukon and Russia, to get a sense of the diversity of the camels.
And there is room for further research, too, into the effect of climate change, which was a major factor in killing off the North American camel population.
The planet is projected to warm another two to three degrees C over the next century, and the researchers suggest that the High Arctic camel presents a possible historical analogue for future warming.