Pictures:"Nasty" Little Predator From Dinosaur Dawn Found

Deadly and dog-size, the dinosaurEodromaeus(shown in reconstruction) lived inArgentina230 million years ago, a new study says. The new species is providing fresh insight into the era beforedinosaursovertook other reptiles and ruled the world, a new fossil study says. (Watch video.)

"This is the most complete picture we have of what a predatory dinosaur lineage– what it looked like at the very beginning,"said study co-authorPaul Sereno."It was small but nasty—this animal was fast."

One of the earliest known dinosaurs,Eodromaeuswas only about 4 feet (1.3 meters) long and would have barely reached the knees of an adult human. But this unassuming little dinosaur gave rise to the theropods, includingTyrannosaurus rexand the"terrible claw,"Deinonychus,the new study suggests.

Like those fearsome descendants,Eodromaeushad a long rigid tail, a unique pelvis shape, andair sacs in its neck bones that may have been related to breathing—and which add to evidence that theropod dinosaurs eventually evolved into today's birds.

(Take adinosaur quiz.)

—Ker Than

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