Edmontosaurus annectens Skeletal fossils as found at the excavation site Locality: South Dakota, USA Formation: Hell Creek Formation These are the skeletal fossils of Edmontosaurus as found at the excavation site when they were first discovered. The bones, scattered randomly, belong to at least four specimens, both fully-grown and juvenile. In the Late Cretaceous, a shallow sea extended north to south along the eastern side of the Rocky Mountains, dividing the North American continent into eastern and western regions. It is believed that these dinosaurs died near a coastal plain, where their bones were buried in the sand and mud that was deposited by a river that changed its course each time it flooded.Fossil : 72 1/2 in. w. x 108 1/2 in. l. x 7 in. h.Crate: 78 in. w. x 112 in. l. x 33 in. h.