Rare Evolutionary Twist Morphed Dino Arms into Bird Wings

When dinosaurs evolved into birds, they had to adapt their arms into wings in order to take flight — a process that altered their skeletal structure. The pisiform, a crumb of bone that helps keeps birds' wings rigid on the upstroke, had vanished in the birdlike dinosaurs that were modern birds' closest ancestors, the researchers report today (Sept. 30) in the journal PLOS Biology. "It is rare," study researcher Alexander Vargas, who leads the ontology and phylogeny lab at the University of Chile in Santiago, told Live Science. Of the few accepted cases of such a disappearing trick, the bird pisiform is among the clearest cases, Vargas said.

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