The distribution of articulated remains of fossil vertebrates is not uniform within the Oldman Formation (Campanian, Cretaceous) of Dinosaur Provincial Park, Alberta. The mesofauna gradually declines in importance from the west to the east, but a corresponding decline in megafauna does not occur until the eastern limit of the park is reached. The mesofauna is also impoverished low in the exposed section, although the megafauna is as abundant there as in higher levels. Woody vegetation may have supported 88% of the megafaunal herbivore biomass. A fine-grained mosaic of several vegetational types was superimposed on a broader west–east gradient of marsh–forest with an abundant mesofauna to an open woodland dominated by hadrosaurids. High densities of large ectothermic dinosaurs would have made intensive use of available vegetation and profoundly influenced landscapes. Distributions of vertebrates in sedimentary units resulting from normal environmental gradients should be distinguished from those postulated to be associated with the onset of changes that brought the Mesozoic to a close.