Vertebrate faunal assemblages of the Late Cretaceous Western Interior Seaway in Manitoba

Abstract

The Late Cretaceous Western Interior Seaway (WIS) vertebrate community zonation hypothesis of two distinct biogeographic subprovinces based upon the distribution of tetrapod fossil occurrences is re-examined for the first time in over 32 years using presence-absence and relative abundance data from all represented vertebrate groups and temporal changes in community similarities throughout the Late Cretaceous examined for the first time. Vertebrate faunal assemblages of the Manitoba (MB) escarpment are compared with those of other coeval WIS assemblages across North America using three community similarity analysis methods, Sorensen’s Coefficient of Community, Percent Similarity, and Non-Metric Dimensional Scaling, to assess community zonation for nine intervals of Late Cretaceous time from the late Cenomanian to early Maastrichtian. At least two-part latitudinal community zonation with a migratory, gradational community boundary is supported throughout the Late Cretaceous, with three-part zonation supported by relatively high genus-level percent similarity values (25-50%) of south-central WIS localities and low values (<20%) of localities furthest north and south for the warmest time intervals, during late Cenomanian to early Turonian and late Coniacian to early Campanian times. Biases including size, geographic, preservational, and taxonomic are described from museum collections of MB escarpment fossils in order to present biogeographic results in an appropriate context, as well as to inform the current study and future studies of associated biases and make recommendations to counteract them with future work. A strong size bias towards the overrepresentation of large-bodied vertebrates from most Upper Cretaceous lithostratigraphic units of MB was revealed through museum collection surveys; therefore, a study of microvertebrate assemblages of the late Cenomanian to mid-Turonian Favel Formation was conducted to counteract this size bias and gain more information with regards to small-bodied vertebrate community members. Examination of Favel Formation microvertebrate fossils has revealed several significant discoveries, including stratigraphic and biogeographic range extensions for several taxa not previously recognized from the Favel Formation, estimation of relative position of the enigmatic northeastern WIS shoreline for three distinct time intervals, and discovery of new microvertebrate material.