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Planet Earth

A New T. Rex Cousin

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Scattered about Madagascar are an odd assortment of dinosaur bones. To some paleontologists, the fossils resemble pieces of a pachycephalosaur (which means "thick-headed lizard"). "Pachycephalosaurs are the dinosaurs that are supposed to have butted heads," says Scott Sampson, a paleontologist at the New York Institute of Technology in Old Westbury. "But that they would be on Madagascar is weird, because pachycephalosaurs are known only from the Northern Hemisphere." On a recent trip to the island, Sampson not only determined that the bones did not belong to pachycephalosaurs; he also found one of the most complete dinosaur skulls ever discovered.

The skull, while complete, was fragmented into about 30 pieces. Oddly enough, paleontologists like to find skulls in such condition. "That's the best-case scenario," says Sampson, "because then you can examine every element from every side and make copies of each, then glue them back together to see what the whole skull would have looked like."

The skull turned out to be that of a large carnivore, perhaps 30 feet long, that was a distant cousin of the tyrannosaurs. The skull has a bony projection on the back and unusually thick nasal bones, says Sampson. "We have scanned several of these elements and found they are hollow. They would not have withstood a lot of stress, including head butting. So they were probably used for show."

The dinosaur, named Majungatholus atopus, has been classified as an abelisauroone of the dominant carnivores in the Southern Hemisphere during the late Cretaceous. (Tyrannosaurs ruled the Northern Hemisphere.) One of the best-known abelisaurs is Carnotaurus sastrei, found only in Argentina. "It is a very strange beast, with one horn over each eye, that was long thought to be unique to Argentinaoan evolutionary dead end," says Sampson. "And now here we found this skull in Madagascar, and other than the horn, it's a dead ringer for the animal in Argentina."

Majungatholus and Carnotaurus lived at around the same timeosome 70 million years ago. Given their similarities, they probably shared a common ancestor not too long before that. "But that doesn't jibe with the general view of how the continents broke up," Sampson says. In fact, geologists have long thought that Madagascar, India, Africa, South America, and Antarctica were isolated from one another about 100 million years ago. "We are arguing nowoas are some geologistsothat connections were retained between South America and Indo-Madagascar, via Antarctica, perhaps as late as 80 million years ago."

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