Planet Earth

The Lowdown on the


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by Eric Powell

Generations of dinosaur enthusiasts have been raised on images of gigantic sauropod dinosaurs gracefully elevating their snakelike necks to munch on Mesozoic treetops or rearing back to intimidate predators. But Roger Seymour, a comparative physiologist at the University of Adelaide in South Australia, says that these majestic behemoths probably never held their heads up high for a pressing reason: heart problems.

Seymour, an expert in the evolution of vertebrate cardiovascular systems, studied Barosaurus, a relative of Apatosaurus (formerly known as Brontosaurus) to infer how its circulatory system worked. The animal would have needed mind-bogglingly high blood pressure— about seven times as high as in humans— to send fluids to a head raised up all the way. According to Seymour's calculations, such an elevated blood pressure would have required an improbably large heart. The left ventricle alone would have weighed two tons— about 5 percent of the creature's body mass and 15 times the weight of the left ventricle of a humpback whale. "That's a big heart," Seymour says. "It would have been hard to fit it in the place where it was supposed to be and get the lungs and other guts in there too." And a heart that massive would have required more than half the food that the animal ate just to keep beating.

A barosaurus with a reasonably sized heart would have had to keep its neck more or less horizontal at all times to avoid passing out, Seymour concludes. Why have such a long neck if you can't lift it up into the air? "Maybe sauropods used their long necks like the hose on a vacuum cleaner, to save energy in browsing on relatively low vegetation," he says.

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