A <i>Spinops sternbergorum</i> (Ornithsichia: Ceratopsia) parietal from the Dinosaur Park Formation (upper Campanian) of Muddy Lake, Saskatchewan

The upper Campanian deposits of the Dinosaur Park Formation at Muddy Lake, Saskatchewan, are known to contain thebones of one or more horned dinosaur species, but definitive diagnostic material has remained elusive. Here, we describe a newly recognized partial parietal from these deposits, bearing a single spike-like epiossification that projects posterolaterally from the frill margin. The element is most plausibly attributable to the centrosaurine Spinops sternbergorum, a species otherwise known only from Dinosaur Provincial Park, Alberta. Juvenile ceratopsids appear to be relatively abundant at the Muddy Lake locality, which was proximal to the Western Interior Seaway. We suggest that such lowland coastal settings might have been important breeding grounds for horned dinosaurs.