Three Cretaceous Euselachian Assemblages from Northern Alberta with Implications for Paleobiogeography of the Western Interior

Assemblages of sharks and rays from the Western Interior Seaway (WIS) in Canada have received less attention than those from the United States. An examination of the euselachian faunal composition within the northern regions of the seaway is essential, as it adds to the biostratigraphic record for temperate-water euselachians and provides insights into the paleoecology, paleoenvironment, and the evolution of these vertebrates.

During the late Albian and Cenomanian, the province of Alberta was situated in the cool temperate climatic zone of the northern region of the WIS. Despite their high paleolatitude, three northern Albertan assemblages have yielded a diverse array of euselachian taxa. The late Albian Paddy Bonebed assemblage consists of at least eight species in five families and two orders, with Hybodus sp. occurring most often. The middle Cenomanian Dunvegan assemblage, dominated by the ray Pseudohypolophus mcnultyi, includes nine species in four families and three orders. The late Cenomanian Watino assemblage consists of 24 species in nine families and three orders. This last assemblage is dominated by the pelagic lamniform shark Squalicorax falcatus. The three assemblages represent the most northern described euselachian assemblages in the WIS. Not only do they extend the northern geographical range of the taxa, but preliminary comparisons with temporally equivalent southern assemblages suggest similar lamniform diversity despite their northern location within the seaway, but low batoid diversity and an apparent absence of squalomorphs. This is in stark contrast to the rich diversity of these taxa in southern seaway assemblages. Further investigations into endemism and bioprovincialism within the northern regions of the WIS will deepen our understanding of euselachian paleoecology throughout Cretaceous North America.