Co-Occurring Campanian/Maastrichtian Index Fossils in the Western Interior and North Pacific Biotic Provinces Require Fundamental Changes in Zonal Biostratigraphy for Both Provinces

New collections from Upper Cretaceous (Campanian-Maastrichtian) deposits found along the west coast of North America, coupled with new collections and analysis of existing collections from coeval strata of the Western Interior, demonstrate the presence of several previously-unrecognized, shared zonal index fossils. We used quantitative, rather than traditionally-used qualitative, characters of cross-section, suture, and ornamentation; we also describe results of new fossil collecting in Baja California and in the Nanaimo Group of Washington State and British Columbia. This work shows that the Western Interior Lower Campanian zonal indices Baculites sp. (smooth) and B. sp. (weak flank ribs), as well as Middle Campanian Baculites sp. (smooth), from the Western Interior are morphologically indistinguishable from Baculites inornatus Meek from the Pacific coast. We also synonymize the west coast Baculites anceps pacificus Matsumoto and Obata, 1963 with Baculites perplexus Cobban, 1962, the west coast Baculites rex Anderson, 1958 with the Western Interior B. gregoryensis Cobban, 1951, and the Western Interior B. cuneatus Cobban, 1962 with the Pacific Coast B. occidentalis Meek 1862. Through comparison to the magnetostratigraphic chron record, we show that the stratigraphic ranges of our studied species-couples are all identical or nearly so, within the margin of error of this method. We also recognize for the first time from the west coast the age-diagnostic ammonites Didymoceras nebrascense, Nostoceras draconis, N. hyatti, N. approximans, and Pachydiscus neubergicus. These new data require fundamental changes to the Campanian biostratigraphic zonations in each province. We believe that the extant cephalopod Spirula spirula provides a good model for the distribution and mode of life of Baculites: an obligatory vertical position in the mid- to upper water column, with passive drifting globally to achieve a cosmopolitan distribution.