Occurrence of <i>Centrosaurus apertus</i> (Ceratopsidae: Centrosaurinae) in Saskatchewan, Canada, and expanded dinosaur diversity in the easternmost exposure of the Late Cretaceous (Campanian) Dinosaur Park Formation

Late Campanian terrestrial communities of western Canada are best known from the fluvial–paralic deposits of the Dinosaur Park Formation (DPF) in Dinosaur Provincial Park (DPP), Alberta. However, a growing list of localities from isolated DPF outcrops, outside of the DPP area, offers a glimpse into palaeocommunities that evolved isochronously with DPP biotas in greater proximity to the Western Interior Seaway. Over the past decade, one such locality was explored along Lake Diefenbaker in Saskatchewan Landing Provincial Park. The initial palaeoecological analysis of this marginal marine community was based on palynomorph and vertebrate microfossil diversity and has laid a foundation for the current study of its monodominant ceratopsian bonebed. The latter has resulted in new occurrences of Centrosaurus apertus and of the elmisaurine Citipes elegans for Saskatchewan based on incomplete yet diagnostic specimens. Centrosaurus apertus is unequivocally identified by a parietal bar bearing two prominent P1 and P2 hooks, which expands the geographical and habitat range of this species to the most coastal environment known from the DPF. Furthermore, the presence of Centrosaurus apertus suggests that the DPF in this region of Saskatchewan is closer in age to the lower DPF than to the uppermost DPF in DPP, which is at odds with a previous palynostratigraphic interpretation. The faunal composition of this bonebed also supports the presence of a widely distributed metacommunity across these deposits. This contribution demonstrates how evidence from multiple localities in the DPF along a spatial gradient, beyond the temporal gradient available within DPP alone, expands the picture of this metacommunity as a potential model system for biotic turnover in response to sea level rise at a geological temporal scale.