Meeting Abstract
P1.142 Tuesday, Jan. 4 New ornithomimid forelimb material from the Late Cretaceous Kaiparowits Formation LAVENDER, Z*; LOEWEN, M; CLAESSENS, L; College of the Holy Cross; Utah Museum of Natural History; College of the Holy Cross lclaesse@holycross.edu
Fossil remains of ornithomimid dinosaurs represent a substantial portion of the theropod material recovered from the Late Cretaceous Kaiparowits Formation, but few of these elements are diagnostic at lower taxonomic levels. A new partial manus of an ornithomimid dinosaur (UMNH VP 16385), including a complete first and second metacarpal, almost complete third metacarpal, second phalanx of digit II, all three unguals, and partial remains of other phalanges can be assigned to the genus Ornithomimus based on metacarpal proportions. Within the genus Ornithomimus currently two species are recognized: O. velox and O. edmontonicus. The metacarpals of O. velox are approximately two-thirds the length of the metacarpals of the type specimen of O. edmontonicus (NMC 8632) and UMNH VP 16385. New fossil preparation of the metacarpals of the O. velox type and the identification of three possible phalanges for this specimen allows a more detailed comparison of metacarpal and phalangeal shape. Currently, the possibility that the O. velox type represents a juvenile form of either O. edmontonicus or UMNH VP 16385 cannot be excluded. However, the temporal distribution of these three specimens, ranging from the Oldman (O. edmontonicus), Kaiparowits (UMNH VP 16385), and Denver Formation (O. velox), potentially separates these specimens by as much as 10 Million years. A fourth specimen from the Horseshoe Canyon Formation, currently referred to O. edmontonicus (ROM 851), differs from UMNH VP 16835 and the O. edmontonicus type in the length of the second phalanx of digit two. The complexities of possible synonomy, potential lack of species level diagnostic characters in the manus and temporal separation of specimens illustrates the uncertainty that exists in Ornithomimus species level systematics, and the potential for the new Kaiparowits specimen to bear light on this problem.
