NEW SPECIMENS OF THE HORNED DINOSAUR TOROSAURUS (DINOSAURIA: CERATOPSIA) FROM THE LATE CRETACEOUS HELL CREEK FORMATION OF MONTANA

The large horned dinosaur Torosaurus is a rare component of the late Maastrichtian vertebrate fauna of western North America. Two nearly complete skulls recently recovered by the Museum of the Rockies from the Hell Creek Formation of eastern Montana allow a better characterization of the cranial anatomy and individual variation within this genus. Areas of variation include overall skull size, size and orientation of the horns, and the size and orientation of the frill. The first specimen, MOR 981, is a crushed partial skull measuring 3.2 meters in greatest length. The second specimen, MOR 1122, is an uncrushed, well-preserved skull measuring approximately 2.8 meters in greatest length. The latter specimen shows several unusual cranial features, including keeled epoccipitals and prominent double sulcations on the postorbital horns. Further study of these Torosaurus specimens will focus on the phylogenetic position of Torosaurus and cranial pathologies in MOR 1122.