Polar dinosaurs provide unique insights for testing hypotheses regarding paleobiology, paleoecology, and paleobiogeography. Critical for such testing is a comprehensive understanding of the taxonomic diversity of contemporaneous polar and lower-latitude paleofaunas. Here we determine the taxonomic identity of a theropod metatarsal that was discovered in the Upper Cretaceous Prince Creek Formation on the North Slope of Alaska. Its morphology and size are most consistent with a metatarsal IV of an ornithomimosaurian or a juvenile tyrannosaurid. Long bone histological analysis reveals a bone tissue composed of fibrolamellar matrix with a mosaic of laminar, longitudinal, sub-plexiform, radiating, and reticular vascularization patterns. The spacing between two outer growth lines diminishes near the periosteal surface, suggesting that the individual was near somatic maturity at the time of death. This finding suggests that its adult body size was comparable to contemporaneous North American ornithomimids, such as Ornithomimus, and much smaller than those of known tyrannosaurids. Thus, we ascribe the Alaskan specimen to Ornithomimosauria, providing new evidence on the known taxonomic diversity of the Prince Creek fauna. Interestingly, the Alaskan specimen primarily shows annuli, which is inconsistent with the pronounced lines of arrested growth (LAGs) reported in the purported southern high-latitude ornithomimosaurian Timimus and observed variably in contemporaneous lower-latitude ornithomimids. Due to this inconsistency, additional dinosaurian specimens are needed to comprehensively examine the relevance of particular histological features to polar climate habitation.
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