Fishes from the Upper Cretaceous Prince Creek Formation, North Slope of Alaska, and their palaeobiogeographical significance

Abstract The Upper Cretaceous Prince Creek Formation (PCF) of northern Alaska offers a unique glimpse into northern high‐latitude, non‐marine vertebrate assemblages, providing critical data on polar ecosystems during the late Campanian ( c . 73 Ma). This study presents a comprehensive taxonomic assessment of fish fossils from the PCF, including macrofossils and microfossils obtained through bulk sampling. The assemblage demonstrates lower species richness compared with penecontemporaneous formations in mid‐latitude North America, with notable absences of typical taxa such as Myledaphus , lepisosteids, and amiids. Teleost fishes dominate the assemblage, comprising both endemic species and taxa shared with the Western Interior. New esocids ( Archaeosiilik gilmulli gen. et sp. nov. and Nunikuluk gracilis gen. et sp. nov.), the earliest known salmonid ( Sivulliusalmo alaskensis gen. et sp. nov.) and the earliest known cypriniform suggest that these fishes possessed unique polar adaptations. The presence of the elasmobranch Squatina , as well as sturgeon and paddlefish in this assemblage further emphasizes the distinctive composition of this high‐latitude ecosystem. These findings suggest that the polar environment significantly influenced fish diversity and distribution, supporting the hypothesis that some taxa, such as esocids and salmonids, were already adapted to higher‐latitude environments during the Late Cretaceous. Additionally, the study expands our understanding of the latitudinal biogeography of Laramidian vertebrates, providing additional support for the hypothesis that a distinct polar faunal province, named the Paanaqtat Province, was present. This research not only enriches the palaeontological record but also offers new insights into the evolutionary and ecological dynamics of polar ecosystems during the Late Cretaceous.