LATE CRETACEOUS MARINE VERTEBRATE FAUNAL ASSEMBLAGES OF THE MANITOBA ESCARPMENT IN SASKATCHEWAN AND MANITOBA, CANADA

Recent stratigraphic work on Late Cretaceous deposits of the Western Interior Seaway (WIS) from the Manitoba Escarpment include an updated lithostratigraphic framework, radiometric ages of bentonites, and foraminiferal zones, however data is currently lacking in terms of vertebrate biostratigraphy. An understanding of the distribution of vertebrates in Saskatchewan and Manitoba is essential in order to test hypotheses of faunal provinciality, habitat preferences, and temporal and spatial changes in WIS faunal assemblages.

In order to examine faunal occurrences, a dataset was compiled of specimens previously collected from the Escarpment that are housed in museums across Canada. A comprehensive biostratigraphic chart was constructed using genera as x values, lithostratigraphic members as y values (accompanied by radiometric ages known to date), and habitat preference defined by colour. These segregations, combined with total estimated specimen quantities for each genus, will allow for reliable definitions of vertebrate biozones and comparisons of environment-equivalent faunas.

Most vertebrate specimens collected from the Escarpment are from the mid-Cenomanian Belle Fourche Member of the Ashville Formation and the early Campanian Pembina Member of the Pierre Shale Formation. Results show the Belle Fourche assemblage is high in osteichthyan and chondrichthyan diversity and low in reptile and avian diversity, whereas the Pembina faunal assemblage is high in reptile and osteichthyan diversity and low in avian and chondrichthyan diversity. Changes in faunal assemblages over time likely reflect changes in the environment from warmer waters in a deeper basin indicated by carbonate deposition in the Cenomanian to cooler waters in a shallower basin in the Campanian represented by clay-rich shales. Members other than the Pembina and Belle Fourche are underrepresented by museum fossil collections and future work will include collecting new specimens to offset historical collection biases. A reliable biostratigraphic framework constrained by absolute ages for the Escarpment will be extremely useful for resolving correlations with other Cretaceous deposits in North America and for addressing questions concerning evolutionary history, ecosystem function, and extirpation events within the WIS.