Modern giraffes face similar challenges, but their necks are "only" about 6.5 feet long. Nevertheless, a giraffe's blood pressure "is about twice that of normal mammals," Seymour said. "If they had 9-meter (29.5-foot) necks, giraffes would be in the same problem as high-browsing sauropods." Seymour's calculations didn't stop there. He determined that the cardiac work rate of a sauropod holding its neck vertically would have been 7.5 times higher than that of many modern animals. This, in turn, would have required a high metabolic rate, with sauropods expending 49 percent of their total energy requirements "just to circulate the blood." Such a supercharged, yet wasteful, cardiovascular system never evolved in sauropods, argues Seymour. "They would have fainted, as you would in less than five seconds without blood flow to the brain," he said. So why did sauropods have such long necks? Octavio Mateus, a paleontologist at the Universidade Nova da Lisboa, believes the reason was sexual selection -- sauropods may have found the trait attractive in potential mates, and longer necks evolved as a result Seymour believes long necks served a number of functions. "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," he said, adding that sauropods could have also used their necks to reach aquatic vegetation from land, or even to feed on the bottom of sea floors "while the body floated." Related Links: |
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