永利网娱乐:Frill chill

 作者:易咣     |      日期:2019-03-08 09:03:02
By Jeff Hecht in Boston WHY did some dinosaurs have bony frills on their skulls? To keep their brains cool, says a palaeontologist who has found the first strong evidence for the idea. Palaeontologists have puzzled over the elaborate horns and frills decorating the skulls of a family of big dinosaurs called Ceratopsians. Perhaps they were a defence against predators such as Tyrannosaurus rex, or attracted mates. But Reese Barrick of North Carolina State University in Raleigh wanted to test the idea that the frills kept the animals cool. The many blood vessels in fossilised frills and horns hinted that they may have dissipated excess heat in the same way that the blood flow through African elephants’ ears helps them cool off. Barrick and his colleagues looked at levels of the rare isotope oxygen-18 in the horns and frills of Triceratops, an elephant-sized Ceratopsian. The ratio of oxygen-18 to oxygen-16 varies depending on the temperature at which bone forms, so levels of this isotope in different parts of fossilised bone reveal the relative temperature distribution when the animal was alive. Barrick’s team found that no part of the dinosaur frill dropped more than 4 °C below the dinosaur’s mean body temperature. This even temperature suggests that the animals continually pumped blood through their frills to get rid of heat (Journal of Vertebrate Paleontology, vol 18, p 746). ” Triceratops was actively using its frill as a heat dump,” Barrick concludes. Horn temperatures varied much more widely, however, with the coldest temperatures at the tips. Barrick believes the dinosaurs dumped heat into the horns only when they were in danger of seriously overheating. He says modern goats do the same when their brains overheat. “Whether or not he has all the details precisely right, I think he’s on the right track,” says Peter Dodson, a palaeontologist at the University of Pennsylvania in Philadelphia. However,