SÃO PAULO, BrazilWhen Neurides Martins brushed the sediment from the tiny tooth, she knew she had found something special.

That tooth was the first piece of a new species of dinosaur, and an unusual one. Roughly the size of a Great Dane, the carnivore would have roamed the desert some 90 million years ago, walking upright on two legs and resting its weight on just one long clawed toe, the middle toe of three.

Almost 50 years ago, paleontologists found mysterious one-toed footprints in the region, but until now, no one knew what creature had made them. While its three functioning toes make the new species a theropod dinosaur like Tyrannosaurus rex, this rare anatomy makes it function essentially