The remains include the lower jaw and back half of the skull, along with neck and back vertebrae , and various limb elements . These fossil remains were discovered in the Mussentuchit Member of the Cedar Mountain Formation in the eastern portion of the U.S . The oldest layer, known as the Yellow Cat Member, contains Gastonia , while the intermediate Poison Strip and Ruby Ranch Members contain remains which may belong to Sauropelta . Fossils in this region are often slightly radioactive , and remains of Animantarx were actually discovered following a radiological survey of the area performed by Ramal Jones, which located a higher level of radioactivity at a certain location . Subsequent excavation at this site turned up the fossil skeleton of Animantarx ; no bones had been exposed on the surface .