Vertebrate palaeocommunities of the lower Judith River Group (Campanian) of southeastern Alberta, Canada, as interpreted from vertebrate microfossil assemblages

A palaeoecological analysis of vertebrate assemblages of the upper Cretaceous Foremost and Oldman Formations based on data from 19 microfossil localities in the Milk River area of southeastern Alberta is presented. R-mode cluster analysis reveals two groups of taxa showing significant difference in their relative abundance. Q-mode cluster analysis, which was used to group sites into clusters containing similar faunal assemblages, resulted in three groups of localities that are highly congruent with their stratigraphic position but not with taphonomic indicators or facies associations. Members of two palaeocommunities are identified based on these distribution patterns. Through comparison with corresponding palaeocommunities previously recognized in Dinosaur Provincial Park, Alberta—about 200 km to the north and largely later in time—the stability of palaeocommunity structure over an approximately 5-million-year time period is evaluated. In general, palaeocommunity structure through the lower beds of the Judith River Group corresponds to the structure of palaeocommunities in the upper beds. Differences can be attributed to extinction events and environmental controls on the north–south distribution of taxa.