Phylogeny and biogeography of some Cretaceous spatangoid echinoids with special emphasis on taxa from the Western Interior Seaway

Members of the echinoid order Spatangoida, a highly diverse and abundant marine invertebrate clade, were important denizens of the Cretaceous Western Interior Seaway (WIS), an epicontinental seaway that divided North America in two during an interval of greenhouse conditions between roughly 100 and 65 million years ago. A phylogenetic analysis of spatangoids was conducted using a character matrix of 32 characters from 21 species.  Species that occur in the WIS were considered comprehensively, and species from other regions such as South America, Europe, and North Africa were also incorporated into the analysis.  Phylogenetic patterns retrieved are largely congruent with pre-existing family-level classifications; however, species within several genera, especially Hemiaster and Heteraster, need to be re-assigned so that classification better reflects phylogeny. The genera Washitaster and Heteraster are closely related, as are Mecaster, Palhemiaster, and Proraster; Pliotoxaster, Macraster,...