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Stegoceras, a pachycephalosaurid (dome-headed) dinosaur, lived in what is now North America during the Late Cretaceous period, about 77.5 to 74 million years ago. (This genus is distinct from Stegosaurus, which lived more than 70 million years earlier.) Small and bipedal, Stegoceras was about 2 to 2.5 metres (6.6 to 8.2 ft) long and weighed around 10 to 40 kilograms (22 to 88 lb). It had a rigid vertebral column and a stiffened tail. The pelvic region was broad, perhaps due to an extended gut. The skull was roughly triangular with a short snout, topped by a thick, broad, and relatively smooth dome. The skull jutted out in the back over the occiput, and had a thick ridge over the eyes. The teeth were small and serrated. The skull is thought to have been flat in juvenile animals, growing into a dome with age. The dome may have been used for combat, display, or recognition. Specimens have been found in the Dinosaur Park and Oldman formations in Alberta, and the Fruitland and Kirtland formations in the US. (Full article...)