Morphological Diversity in Bearpaw Mosasaurs

Abstract

Previous problems with character state constructions in maximum parsimony analyses cause resulting phylogenies to be affected by subjectivity of anatomical features and bias. A new taxonomic character matrix designed to better assess morphological diversity in Squamates is applied to specimens of M. missouriensis and Mosasaurus sp. from the Bearpaw formation in southern Canada, placing them within a larger assemblage of mosasaurines. Several polytomies and low bootstrap support in the resulting consensus tree suggest that a lack of available data due to preservation and taphonomic effects still hinders the resolution of maximum parsimony analyses, despite improved character construction. Most Bearpaw specimens formed a polytomy in a sister clade to a clade containing a separate polytomy of M. hoffmanii, M. missouriensis, M. lemonnieri, and M. mangahouangae, possibly indicating certain region-specific morphologies. However, taxonomic assignment and relative contribution of interspecific versus intraspecific variation among the Bearpaw specimens remains unclear. Construction of a new taxon specific to the Bearpaw formation is not strongly supported.