How did the camel get his hump?
With the announcement Tuesday that a Canadian-led research team has discovered prehistoric camel fossils in the high Arctic, that story is about to get a lot more interesting.
Fat-filled humps may have been an adaptation for surviving in the chilly polar forest, according to the lead author of the new findings.
“This completely changes how we think about the evolution of Paracamelus, which is the form that gave rise to the modern camel,” says Natalia Rybczynski, a paleobiologist at the Canadian Museum of Nature in Ottawa and a professor at Carleton University. The research is published in the journal Nature Communications.
The find is “mind-boggling,” says Kevin Seymour, a paleobiologist at the Royal Ontario Museum who was not involved in the study. “That’s what the far north does: it serves up these surprises every now and then.”
The fossil fragments were collected from a site on Ellesmere Island over the course of three field seasons starting in 2006. That first year was an exceptionally buggy one, Rybczynski remembers. Scrabbling around in the dirt with her vision obscured by a bug net, she found what she thought might be ancient wood, and pocketed it.
Back at base camp, she got excited: it was fossilized bone. While preserved plant material is abundant in the high north, it’s rare to find animal deposits.
“Everything we find is interesting and important, because it’s so close to this area of interchange and change between the continents,” says Rybczynski.
The Arctic is also an important region because it is so sensitive to climate fluctuations, she adds. The fossil fragments date to a warm period 3.5 to 4 million years ago called the mid-Pliocene, when global mean temperatures at that point were only two to three degrees warmer than today. But the Arctic was as much as 18 degrees warmer, with mean temperatures hovering around zero.
The animal, whatever it was, would have lived in a boreal forest thick with larch trees. Much of the now-icy sea was filled in with sediment.
As more fossil fragments were discovered, clues about the prehistoric animal began to emerge. The bone was a tibia, or lower leg bone, with the distinctive traits of cloven-hoofed animals like deer and hogs.
It was also massive. That suggested it was probably from a prehistoric camel, which were the most prevalent ungulates, or mammals that are usually hoofed, on the continent during the mid-Pliocene. The camel family actually originated in North America. But while prehistoric camel fossils were discovered in the Yukon in 2011, none have ever been found in the high Arctic, a very different ecological niche.
A chance encounter at a conference strengthened the camel argument. Rybczynski heard Mike Buckley, a research fellow at University of Manchester, speaking about cutting-edge collagen “fingerprinting” techniques. DNA decays quickly in bones. But collagen lasts longer, and scientists have discovered how to extract from it a distinctive molecular fingerprint for a given species. So Rybczynski sent him a piece of the Ellesmere Island fossil.
Its collagen fingerprint was a near-identical match to the dromedary, the single-humped modern species. It was also matched the Yukon fossil.
Those were “very surprising” findings, says Buckley.
Until now, paleobiologists believed that the most recent ancestor of modern camels, Paracamelus, evolved in the arid grasslands and deserts of Eurasia after much earlier prehistoric camels crossed over the Bering Strait from North America.
But this evidence suggests that Paracamelus lived in high latitudes of North America too, and in fact probably originated there. It flips our image of a grazing-specialized species on its head: the camel may have originally been a boreal-forest specialist.
That would help explain some features of camels, including dental traits similar to deer and moose. And it might explain the humps, which scientists now know are filled with fatty tissue, not water. The survival of mammals in the polar north can usually be predicted by its body fat at the start of the season.
Oddly, some of those same adaptations may also help in the camel’s modern environment; Rybczynski theorizes that an arid desert and a frozen forest are not that different from an herbivore’s perspective.
“It’s just so neat to look at this animal and how adaptive it is,” she says.
The team will continue its missions to the high Arctic, and hopes to discover more about this animal and others.
“It’s a huge part of country, very poorly known, with lots of discoveries to be made,” says the ROM’s Seymour.
“The Canadian north is so wide open for discoveries; it’s just a matter of getting there.”
