The 3-foot-long crocodile-like reptiles, called Revueltosaurus callendari, were first thought to be plant-eating dinosaurs, but scientists soon determined they weren't, the (Flagstaff) Arizona Daily Sun reported Thursday.
"We realized that it wasn't a dinosaur. It was a whole new family of reptile that no one had ever seen before," Bill Parker, park paleontologist, said.
Eleven fossil specimens of the creatures were found together, suggesting some event wiped out all 11 at once in the same location.
That may have been something like a flood, Parker said, since -- when the creatures existed around 213 million years ago -- northern Arizona was closer to the equator and parts of the land contained large rivers.
"It was a one-time event that killed them, and all those animals were together for some reason," Parker said.
Similar in appearance to a modern Komodo dragon, they possessed iguana-like teeth and probably ate plants, insects or small animals, and had armored portions along some parts of the body, researchers said.