The dinosaur in question was a plant-eating animal 13 feet long and weighing 660 pounds that lived and died not long before the extinction of all dinosaurs, which occurred about 65 million years ago. In 1993, Mr. Hammer found the skeleton embedded in sandstone in Harding County, in northwestern South Dakota. The fossils were acquired by the North Carolina museum three years later, where they are on display.The specimen has been identified as a member of the Thescelosaurus, meaning ''marvelous lizard,'' genus. Its species has not been determined. For the time being, the dinosaur usually goes by the nickname Willo, after the wife of the rancher on whose land it was found.