First articulated ornithomimid specimens from the upper Maastrichtian Scollard Formation of Alberta, Canada

Abstract

ABSTRACT Despite an abundance of ornithomimid fossils from the Late Cretaceous of Alberta, Canada, only isolated elements are known from the upper Maastrichtian Scollard Formation. Ornithomimus velox and Struthiomimus sedens are the two taxa recognized from penecontemporaneous formations in the U.S.A., but the incomplete nature of these specimens and the lack of contemporary material from Alberta creates a gap in our understanding of ornithomimid diversity during the late Maastrichtian of North America. Here, I describe the first diagnostic ornithomimid fossils from the upper Maastrichtian Scollard Formation of central Alberta, Canada, providing new information about the taxonomic composition of North American ornithomimids during the late Maastrichtian. The first fossil, an articulated forelimb, exhibits metacarpal ratios and features of the manual unguals that support its referral to the genus Ornithomimus. The second fossil, an associated hind limb, belongs to a large-bodied ornithomimid, and based on characteristics of the pedal unguals is assigned to the genus Struthiomimus. Based on these taxonomic designations, the stratigraphic ranges of both Ornithomimus and Struthiomimus are extended from the upper Campanian Dinosaur Park Formation through to the upper Maastrichtian Scollard Formation of Alberta, which constitutes more than 10 million years of time. These specimens offer new knowledge on the taxonomic composition of ornithomimids in Alberta, but the unusually long stratigraphic range coupled with the difficulty in diagnosing either specimen to species underscores the need for review of North American ornithomimid taxonomy.