Codex Eurypterida

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Codex Eurypterida: A Revised Taxonomy Based on Concordant Parsimony and Bayesian Phylogenetic Analyses

Abstract

Eurypterids, also known as sea scorpions, were aquatic chelicerate arthropods that were important components of Paleozoic marine and freshwater ecosystems from the Ordovician to the Permian. The group represents an excellent subject for studies into evolution due to their exceptionally preserved fossils which frequently reveal almost complete details of the exoskeleton, including the appendages, which allows for interpretation of their roles in ancient ecosystems. This contribution presents an overview of the 200-year history of eurypterid research and their occurrence in popular media before presenting an updated classification for Eurypterida based on concordant parsimony and Bayesian phylogenetic analyses of 238 morphological characters coded for 152 species. This represents the first comprehensive treatment of eurypterid systematics in 35 years and includes evaluation of every known described species of eurypterid. In the process several species names occurring in the Russian literature are shown to be invalid. The appropriate taxonomic authorities for Eurypterida, Stylonurina, and Eurypterina are revised and a revision conducted of all known species. Eighteen new taxa are proposed; the superfamily Waeringopteroidea, the families Brachyopteridae, Stylonurellidae, Strobilopteridae, Waeringopteridae, Nanahughmilleriidae, Parahughmilleriidae, Pittsfordipteridae, Ciurcopteridae, Herefordopteridae, and Hunanopteridae, and the genera Athenepterus, Waterstonopterus, Barusopterus, Cruinnopterus, Selkiepterella, and Hunanopterus. The species name Strobilopterus proteus is also formally made available for the first time. Eurypterid anatomical terminology is updated and standardized. Reviewing previous analyses of macroevolutionary and macroecological trends within eurypterids in light of the revised relationships suggested here indicates that their conclusions are still generally supported, although the history of eurypterid geographic occurrence and dispersal is more complicated than previously considered. Recent discoveries of eurypterids from the paleocontinent of Gondwana represent some of the more exciting new developments in eurypterid research and it is likely that more eurypterids will be found in these regions in the future. Ongoing research into eurypterid ontogeny and macroevolution is detailed and understudied aspects of eurypterid paleobiology, including their ichnological record, role in paleocommunities, and taphonomy are explored. Suggestions are made for inroads into these relatively neglected research programs. Common misconceptions about eurypterids are also addressed; no eurypterid is known to possess a venomous sting in its tail, and while eurypterids likely congregated to shed their exoskeletons there is no compelling evidence that they mated en masse.