Diversity of late Maastrichtian tyrannosauridae (Dinosauria: Theropoda) from western North America

The tooth taxon Aublysodon mirandus was reinstated following the collection of nondenticulate tyrannosaurid premaxillary teeth from late Maastrichtian deposits in western North America. A small skull from the Hell Creek Formation of Montana (the 'Jordan theropod', LACM 2847 1), that was associated with a nondenticulate premaxillary tooth, was referred to Aublysodon and the diagnosis was revised to include cranial bones. However, the 'premaxillary' tooth of the specimen is actually a maxillary tooth. The small size of Aublysodon crowns, and evidence that some denticles develop late in growth in theropods, indicates that the nondenticulate condition represents immaturity. Therefore, Aublysodon is a nomen dubium. The Jordan theropod was recently designated as the type specimen of Stygivenator molnari. A tyrannosaurid from the Hell Creek Formation of Montana (LACM 23845) was first referred to Albertosaurus cf. A. lancensis and then later became the type specimen of Dinotyrannus megagracilis. On the basis of shared derived characters and a quantitative reconstruction of the growth series of Tyrannosaurus rex, the type specimens of S. molnari and D. megagracilis are juvenile and subadult specimens of T rex, respectively. There is currently evidence for only one tyrannosaurid species in the late Maastrichtian of western North America: T rex. (C) 2004 The Linnean Society of London, Zoological Journal of the Linnean Society, 2004, 142, 479-523.