A high latitude vertebrate fossil assemblage from the Late Cretaceous of west-central Alberta, Canada: evidence for dinosaur nesting and vertebrate latitudinal gradient.

This study reports on a new microvertebrate locality from the Campanian (c74 My) fluvial beds of theWapiti Formation in the Grande Prairie area (west-central Alberta, Canada). This locality represents deposition on a low-gradient, waterlogged alluvial plain approximately 300 km to the north west of the Bearpaw Sea. Detailed sedimentological analyses suggest an environment characterized by a high-sinuosity channel system responsible for widespread oxbow lakes, bogs and marshes. A total of 260 identifiable elements were recovered from three distinct sites at the Kleskun Hill Park, documenting a diverse terrestrial and fresh-water palaeocommunity. The recovered fossils include those from hatchling- to nestling-sized hadrosaurid dinosaurs, indicating the presence of a nesting ground in the area. This is the first evidence for dinosaur nesting site in the Wapiti Formation and simultaneously an extremely rare evidence of high-latitude dinosaur nesting, the northernmost in North America to date. A large number of teeth of the small theropod Troodon are associated with baby hadrosaurids in the site supporting a northern affinity of this taxon as well as a previously proposed predator–prey association. Other dinosaurs are less common at the locality and include large and small theropods (i.e. tyrannosaurid, Saurornitholestes, Richardoestesia, Paronychodon, and dromaeosaurid) and five ornithischian taxa. Fish, squamate, turtle, and mammal elements were also identified. Collectively, the vertebrate fossil assemblage from the locality allows palaeocommunity reconstruction in the Wapiti Formation. The importance of the data collected from the new locality is twofold: first, they represent the first comprehensive report from a geographically significant area located between the well-sampled fossil localities of southern Alberta and the high-latitude localities of Alaska. Furthermore, the reconstructed vertebrate fauna support latitudinal gradient of vertebrate distribution along the Western Interior region during the Late Cretaceous.