A prevalence ofArthropterygius(Ichthyosauria: Ophthalmosauridae) in the Late Jurassic—earliest Cretaceous of the Boreal Realm

Abstract

The ichthyosaur genusArthropterygiusMaxwell, 2010 is considered as rare and poorly known. However, considering the existing uncertainty regarding its position in respect to ophthalmosaurid subfamilies in recent phylogenies, it is among the key taxa for understanding the evolution of derived Late Jurassic and Early Cretaceous ichthyosaurs. Recently excavated unique material from the Berriassian of Franz Josef Land (Russian Extreme North) and examination of historical collections in Russian museums provided numerous specimens referable toArthropterygius. The new data combined with personal examination of ichthyosaursPalvennia,Janusaurus, andKeilhauiafrom Svalbard give us reason to refer all these taxa toArthropterygius. Therefore, we recognize four species within the genus:Arthropterigius chrisorum(Russell, 1994),A. volgensis(Kasansky, 1903) comb. nov.,A. hoybergeti(Druckenmiller et al., 2012) comb. nov., andA. lundi(Roberts et al., 2014) comb. nov. Three of the species are found both in the Arctic and in the European Russia. This allows the suggestion thatArthropterygiuswas common and widespread in the Boreal Realm during the Late Jurassic and earliest Cretaceous. The results of our multivariate analysis of ophthalmosaurid humeral morphology indicate that at least some ophthalmosaurid genera and species, includingArthropterygius, could be easily recognized based solely on humeral morphology. Our phylogenetic analyses place the clade ofArthropterygiusclose to the base of Ophthalmosauria as a sister group either to ophthalmosaurines or to platypterygiines. Although its position is still uncertain, this is the best supported clade of ophthalmosaurids (Bremer support value of 5, Bootstrap and Jackknife values exceeding 80) that further augments our taxonomic decision.