Well, at least turkey size. Researchers led by Paul Sereno of the University of Chicago and Alfredo Monetta of the National University of San Juan, Argentina, dug up its 225 million-year-old fossilized skull in the foothills of the Andes in October 1991. By the time they announced the find last week in the journal Nature, they knew it was the most primitive dinosaur ever discovered and just a couple of evolutionary steps away from the ancestor of them all. Of course paleontologists knew that everything from lumbering stegosaurus to ferocious deinonychus must have evolved from something less imposing, but this scrawny thing was pushing it: Eoraptor (“dawn stealer”) was a fleet-footed, bipedal carnivore with none of the specialized features found in later dinosaurs.
The surprise is how diverse dinosaurs were from the outset. The profusion of types-big and small, two-legged and four-legged-came so suddenly that Sereno suspects they did not have “a nice, stately evolution.” Instead, they probably burst on the scene after a climate or geological change and sprouted into enough different forms to fill just about every niche on earth. So Eoraptor may have something to say about the pace and mechanisms of evolution. Especially if another scientist stumbles across this turkey’s ancestor.
