Imagine a monster with the teeth of a shark, the talons of an eagle, the neck of an antelope and the hindquarters of an ostrich. A mythological chimera? Not at all. "I stepped down into this gulch," recounts University of Chicago paleontologist Paul Sereno, "took 25 steps and screamed." Directly ahead, atop a sandstone knoll, lay the full skeleton of a 2-meter-long (about 6 ft.) carnivore. It proved to be the most ancient dinosaur discovered to date.
Last week, at the meeting of the Society of Vertebrate Paleontologists in Austin, Sereno for the first time revealed details of the find, made...