Needle-like teeth spike a full-size replica of the skull of the new Eodromaeus dinosaur, held by University of Chicago paleontologist Paul Sereno, also a National Geographic explorer-in-residence. (The National Geographic Society owns National Geographic News.)
Eodromaeus lived alongside—and now appears to have, in a sense, taken the place of—a very similar dinosaur species, Eoraptor (picture), Sereno said. "If you went back 230 million years ago and one of these creatures flitted by, you'd have to wonder which one it was."
Sereno and his team once thought Eoraptor was an ancestor of meat-eating dinosaurs. But due to recent analysis of Eoraptor fossils, as well as the discovery of Eodromaeus, he now thinks Eoraptor was an ancestor of the giant, long-necked, plant-eating dinosaurs called sauropods.
"That's the beauty of dinosaur origins," Sereno said. "Who could predict that these 10- to 15-pound [4.5- to 7-kilogram] creatures—both looking quite similar but eating different things—would end up evolving into things as disparate as Diplodocus and Tyrannosaurus?"
The reclassification of Eoraptor makes sense, agreed Hans-Dieter Sues, a dinosaur expert at the National Museum of Natural History in Washington, D.C., who was not involved in the study.
"One thing that everyone noticed when Eoraptor was first discovered was that the back teeth were very odd-looking for a theropod," said Sues, also a contributing editor to the National Geographic News Watch blog. "It had these little leaf-shaped teeth in the back, and those are teeth you don't really find in theropods."
(Related: "Smallest Meat-Eating Dinosaur in North America Discovered.")