Vertebrate Anatomy Morphology Palaeontology 8:67–95 67 ISSN 2292-1389 A subadult individual of Styracosaurus albertensis (Ornithischia: Ceratopsidae) with comments on ontogeny and intraspecific variation inStyracosaurus and Centrosaurus Caleb M. Brown1,*, Robert B. Holmes2, Philip J. Currie2 1Royal Tyrrell Museum of Palaeontology, Box 7500, Drumheller, AB, T0J 0Y0, Canada;
[email protected] 2Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada;
[email protected];
[email protected] Abstract: Styracosaurus albertensis is an iconic centrosaurine horned dinosaur from the Campanian of Alberta, Canada, known for its large spike-like parietal processes. Although described over 100 years ago, subsequent dis- coveries were rare until the last few decades, during which time several new skulls, skeletons, and bonebeds were found. Here we described an immature individual, the smallest known for the species, represented by a complete skull and fragmentary skeleton. Although ~80% maximum size, it possesses a suite of characters associated with immaturity, and is regarded as a subadult. The ornamentation is characterized by a small, recurved, but fused nasal horncore; short, rounded postorbital horncores; and short, triangular, and flat parietal processes. Using this specimen, and additional skulls and bonebed material, the cranial ontogeny of Styracosaurus is described, and compared to Centrosaurus. In early ontogeny, the nasal horncores of Styracosaurus and Centrosaurus are thin, recurved, and unfused, but in the former the recurved morphology is retained into large adult size and the horncore never develops the procurved morphology common in Centrosaurus. The postorbital horncores of Styracosaurus are shorter and more rounded than those of Centrosaurus throughout ontogeny, and show great- er resorption later in ontogeny.