Vertebrate Biogeography of the Late Cretaceous (Cenomanian-Maastrichtian) Western Interior Seaway of North America by Percent Community Similarity with the Faunal Assemblages of south-central Canada

Community zonation of the Late Cretaceous Western Interior Seaway (WIS) of North America has been suggested for bivalves, cephalopods, foraminifera, gastropods, and tetrapods. Most proposed WIS community zones consist of a northern and southern subprovince with a gradational boundary in central or south-central North America. Since it has been over three decades since the WIS community zonation hypothesis has been investigated for vertebrates, new information including recent radiometric age determinations, taxonomic revisions, additional fossil discoveries, and recently available online museum specimen catalogues allow for testing of the community zonation hypothesis using an updated dataset. Community percent similarities were calculated between time-averaged, lithostratigraphic unit faunal assemblages of the Manitoba escarpment and other WIS localities using Percent Similarity coefficients calculated from relative abundance data as well as Sorensen’s Coefficients of Communities calculated from presence-absence data on the generic and species levels for comparisons. Additionally, nine time bins were used to represent nine Upper Cretaceous lithostratigraphic units of the Manitoba escarpment to test the zonation hypothesis consistency for nearly the entire Late Cretaceous time interval (~71-95 Ma). Relatively high genus-level community similarity values (25-50%) of south-central WIS localities and low values (<20%) of localities furthest north and south support the existence of a central subprovince during Late Cenomanian to Early Turonian and Late Coniacian to Early Campanian times, when the gradational subprovincial boundary would have been furthest south between the Kansas and Texas localities in the USA. Comparatively low genus-level community similarity values (<25%) of all localities south of Manitoba, Canada during mid-Cenomanian and Early to mid-Campanian times indicate the southern subprovincial boundary was furthest north between the Manitoba and South Dakota, USA localities during these time intervals and had migrated throughout the Late Cretaceous. This work highlights significant fluctuations in vertebrate community zonation throughout the WIS through time and space and offers insight into the magnitude of compositional changes that can occur in shallow marine vertebrate communities over a nearly 25 million year interval. Recent work addressing the collection biases apparent in existing museum collections of Cretaceous vertebrate fossils, including preferential sampling of large size classes and certain geologic units, highlights the increased discovery potential of addressing fossil collection biases and the valuable insight into ancient ecosystems that can be obtained.