TELEOSTS FROM THE UPPER CRETACEOUS (CAMPANIAN) JUDITH RIVER FORMATION, NORTH-CENTRAL MONTANA -- EVIDENCE FROM VERTEBRATE MICROFOSSIL LOCALITIES

The diversity and relative abundance of teleosts in the Judith River Formation of Montana was evaluated on the basis of tooth-bearing elements and precaudal centra from vertebrate microfossil localities. Thirteen operational taxonomic units (OTUs) were recognized. Differences in the composition of the teleost assemblage from the Judith River Formation of Montana and contemporaneous beds in Alberta include differences in taxonomic composition and differences in relative abundance of taxa present. Nine of OTUs from Montana do not differ significantly from those from Alberta. Four of the OTUs present in the Judith River Breaks are close to taxa in Alberta but differ in small but taxonomically significant features. The differences in the taxonomic composition of the teleost assemblage from these two regions are significant in evaluating the level of ecological specialization and complexity of the trophic structure of the Late Campanian ecosystems. Based on successional ecology models, stable, long established communities should have high levels of diversity, indicating that higher levels of ecological specialization and more complex trophic structures were present, while communities that are stressed or in a recovery phase would be expected to be low in diversity and composed of numerically abundant, ecological opportunists or generalist bloom taxa. Thus the presences of differences in the teleost assemblages of the Judith River Formation of Montana and equivalent beds in Alberta suggest that the vertebrate assemblages from these regions are part of a mature, stable community.