A major microfloral change takes place at the top of the Nevis coal seam in south-central Alberta. This change corresponds to a regional microfloral break recorded at the Cretaceous–Paleocene boundary in the northwestern interior of the United States. However, dinosaurs cf. Tyrannosaurus rex and Triceratops albertensis have been found in strata between the Nevis and Ardley coal seams at a stratigraphically higher level than that at which palynofloral change occurs in Alberta. This indicates that the floral extinctions slightly preceded the dinosaurian extinction and also implies that the two events were not linked in a direct cause and effect relationship. The presence of dinosaur remains a few metres above the level of microfloral change signifies that the floral change occurred slightly before the end of Cretaceous time. In the northwestern interior of the United States, however, the dinosaurian extinction apparently coincides with the regional palynofloral change recorded at the Cretaceous–Paleocene boundary. It seems that the lime relationship of the microfloral change and the dinosaurian extinction cannot be clearly seen in condensed sections, where they appear to coincide. This relationship becomes more evident in expanded clastic intervals, rapidly deposited under fluviatile sedimentary regimes, in which the datum marking the microfloral change clearly precedes the reptilian extinctions. The corroborative evidence of radiometric age, youngest dinosaur remains and regional microfloral change favours placing of the Cretaceous–Paleocene boundary at the base of the Ardley seam No. 14 in Alberta.