Taxonomy and historical inertia: Clidastes (Squamata: Mosasauridae) as a case study of problematic paleobiological taxonomy

Abstract

I review the taxonomic history of two problematic mosasaur species, Clidastes liodontus and Clidastes moorevillensis. The genus Clidastes is thought to represent an early radiation of a diverse clade known as the Mosasaurinae. However, most phylogenetic analyses recover the genus as paraphyletic with respect to more highly nested mosasaurines such as Mosasaurus, Prognathodon, and Globidens. The fragmentary holotype of Clidastes liodontus was never figured or fully described, and was destroyed in World War II. Over 20 years after destruction of the holotype, relatively complete specimens were referred to Clidastes liodontus based upon a single, variable character. Another taxon, originally designated Clidastes liodontus moorevillensis in a master’s thesis and then elevated to Clidastes moorevillensis in a separate dissertation, has never been formally described and lacks definitive diagnostic characters that differentiate it from the contemporary concept of Clidastes liodontus. Clidastes provides an excellent example of how historical inertia in taxonomic nomenclature can build over decades and skew our interpretations of the diversity, paleobiology, biogeography, and biostratigraphy of a taxon. Clidastes liodontus is a nomen dubium and Clidastes moorevillensis a nomen nudum. I recommend that both names be abandoned. Removal of those names frees us from a burdensome taxonomy and eliminates cognitive biases that hinder objective understanding and exploration of early-diverging mosasaurines, and is a necessary first step toward a taxonomic revision of the lineage(s) involved.