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A NEW, LARGE ORNITHOMIMID FROM THE CRETACEOUS DINOSAUR PARK FORMATION OF ALBERTA: IMPLICATIONS FOR THE STUDY OF DISSOCIATED DINOSAUR REMAINS
Only two ornithomimid genera, Ornithomimus and Struthiomimus, are currently known from the Upper Cretaceous of North America. However, a number of ornithomimid elements from Alberta’s Dinosaur Park Formation (Upper Campanian), cannot be assigned to either Ornithomimus or Struthiomimus. These bones, including a frontal, caudal vertebrae, and unguals of the manus and the pes, come from animals significantly larger than any previously known Judithian ornithomimid. The frontal exhibits several unusual features, including transverse expansion over the prefrontals, and extreme reduction of the supratemporal fossae. Caudal vertebrae are characterized by neural arches that are posteriorly shifted and transversely expanded. Manual unguals possess a highly concave articular surface, a flexor tubercle divided by a sulcus, and a broad claw. Pedal unguals display highly concave articular surfaces, and a ridge-like flexor tubercle dividing a deep ventral fossa. Although it is difficult to know whether these elements represent a single taxon, this is currently the most parsimonious hypothesis. This study demonstrates how isolated dinosaur bones can extend our knowledge of dinosaur faunas.
Elements described in this paper and their position in the ornithomimid skeleton (Struthiomimus altus is shown for reference). A, frontal. B, manual ungual. C, pedal ungual. D, distal caudal vertebra.