Today, Camels! Because I've just learned something about them that was a bit of an eye-opener. There are more than 200 species of artiodactyls but the Family Camelidae has only 6 members: the two remaining "true" camels Camelus dromedarius one-hump Dromedary and Camelus bactrianus two-hump Bactrian camel. These are native to a swathe North Africa and SW Asia. The 300,000 camels running wild in Western Australia are mostly D-camels and both sorts were introduced as beasts-of-burden by the Brits in the mid-19thC. There were a lot more camels in 2009 before a plan to cull them was implemented. Then there is a clatter of South American species:
- llamas Lama glama the domestic form of the guanaco Lama guanicoe
- alpaca Vicugna pacos the domestic form of the vicuña Vicugna vicugna.
One of the legs on which Darwin and Wallace and their contemporaries stood to build the over-arching explanatory edifice of evolution was biogeography. The geographical distribution of today's species gives important clues about how they evolved - Wallace Line, for example. With Camelids divvied up on two distant continents, it's not obvious where they came from. It's hard to imagine them dispersing across the Pacific on a mat of vegetation. Well it turns out that neither South America, Africa or Asia is the answer. The first appearance of two-digit walkers was in the Eocene 45 mya of North America! These camel-like creatures grew and diversified and spread out South down the isthmus of Panama and West across the Bering land-bridge and then died out in the continent of their birth. The last camels 'went West' across the sky-bridge to heaven as part of the great North American mega-faunal extinction of 10,000 years ago; probably driven there by relentless hunting of anything bigger than a breadbox by the ancestors of Native North Americans.
What do we know about camels? They are the ships of the desert, able to walk for days across the shifting sands of the Sahara without water. Their feet are uniquely adapted to traction on those shifting sands, we now know that the hump is not a water bowser but filled with fat. But we're told that in metabolising that fat for energy, water is a chemical by-product and this is recycled. Oh yes, and they spit. About ten years ago Natalia Rybczynski was hunting fossils at the Fyles Leaf Bed in the Canadian High Arctic, like Neil Shubin, except that she was looking for more recent material than the Devonian. She picked up a rock from the tundra, thinking it was a fossil stick and realised that it was a fragment of a fossil femur. Over the next several seasons (!) she went to the same spot and collected 30 fragments of the 3-D jigsaw. Collaboration with Mike Buckley at U.Manchester in England used variation in the collagen molecules (you and I have 40+ different collagen genes each making a different protein) to show that this femur probably came from a camel. Traditional palaeontological techniques showed that the camel had lived 3.5 million years ago and was more than 3m tall. Despite the climate being generally warmer, it was still cold up there, then and the handful of bone fragments suggested a complete turn-around about the what and why of camels.
Maybe the broad feet evolved for walking on snow rather than sand? Perhaps the back-pack of fat was just that, not a surrogate water-store: it supplied the energy necessary to survive through a 6-month long Winter. Maybe not, you have to wear your skeptics hat when a journalist extrapolates from a little bone to a big neat story that can be tied up with a ribbon and presented as a TED talk.
And of course don't forget one of the most interesting thing about camelids...they have weird antibodies. Making them unique among mammals.ReplyDelete