18 oct 2011
(Brachiosaurus
For years now, paleontologists have been debating about how gigantic plant-eating dinosaurs, known as sauropods, held their long necks. Could they stretch their tall necks upright, as giraffes do today, or did they hold them horizontally, more parallel to the ground?
Physiologist Roger Seymour of the University of Adelaide in Australia has long been a proponent of the second low and slow theory. In 2009 he told me, "Like a vacuum cleaner, a long neck would have allowed feeding to perhaps 19.6 feet in height without moving the bulk of the body."
Other scientists have since run with that comparison to canister-style vacuum cleaners and have set out to prove or disprove it. Most recently, evolutionary ecologists Graeme Ruxton of the University of Glasgow and David Wilkinson of Liverpool John Moores University developed a mathematical model to virtually test how dinosaurs such as Brachiosaurus, with its near 30-foot-long neck, moved.
The researchers took into account not only this neck length, but also the weight (over 120,000 pounds) and body measurement—comparable to three school buses—for Brachiosaurus. The scientists also plugged in the numbers for Apatosaurus, another huge plant-eating dinosaur.
Before Ruxton and Wilkinson concluded their work, they predicted in a Royal Society Biology Letters paper "that small extensions of the neck beyond the minimum required for the mouth to reach the ground bring substantial energetic savings. Each increment of length brings a further saving, but the sizes of such benefits decrease with increasing neck length." Beyond that, they also predicted that the super long neck of a dino such as Brachiosaurus would "reduce the overall cost of foraging by 80 per cent, compared with a minimally necked individual."
(Brachiosaurus compared to a huma
Their model supported these predictions.
The researchers now "argue that the long neck of the sauropods may have been under positive selection for low foraging (instead of, or as well as, exploitation of high foraging), if this long neck allowed a greater area of food to be exploited from a given position and thus reduced the energetically expensive movement of the whole animal."
This gets back to Seymour's vacuum analogy. A 1950s-style cylinder vacuum provides the best comparison. The heavier bodied base of the machine often remains still while the long hose moves around to suck up dirt. The dinosaurs weren't exactly sucking, but it's thought that many simply tore off plant material, such as leaves, with their teeth and swallowed this mass whole.
With just the neck probably doing most of the maneuvering and work, it's no wonder that these dinosaurs wound up so fat, save for their long skinny necks.
The debate on how sauropods held their necks will no doubt go on, but I think the scientists put forth a pretty strong argument. Added to it is evidence that long-necked dinosaurs would have fainted all of the time if they held their necks vertically due to a lack of blood flow to their brains. As Seymour says, "Let's just leave it there and not ask the sauropods to raise their necks."
