The taxonomic utility of forefin morphology in Lower Jurassic ichthyosaurs: <i>Protoichthyosaurus</i> and <i>Ichthyosaurus</i>

The validity of the parvipelvian ichthyosaur genus <i>Protoichthyosaurus</i> was evaluated by examining the type material and recently recognized specimens. <i>Protoichthyosaurus</i> has a wide forefin with at least five primary digits, an anterior digital bifurcation in the forefin, a humerus that is nearly equal in width distally and proximally, and a coracoid with well-developed anterior and posterior notches, features it shares with the more common genus <i>Ichthyosaurus</i>. Previously, <i>Protoichthyosaurus</i> was synonymized with <i>Ichthyosaurus</i> because of an incomplete understanding of forefin variation in the latter taxon. However, <i>Protoichthyosaurus</i> has several features in the forefin that distinguishes it from <i>Ichthyosaurus</i>, including the presence of three elements in the distal carpal row, a contact between distal carpal 3 and the ulnare, a bifurcation of distal carpal 2 to form two elements in the metacarpal row, the proximal element of the bifurcation nearly separating distal carpal 2 from distal carpal 3, distal carpal 3 separating the intermedium from contact with distal carpal 4, and the absence of digit V. A phylogenetic analysis confirms that <i>Protoichthyosaurus</i> is the sister taxon of <i>Ichthyosaurus</i> and is nested in Ichthyosauridae. We recognize two species, <i>P. prostaxalis</i> and <i>P. applebyi</i>, sp. nov., but not <i>P. prosostealis</i>. <i>Protoichthyosaurus</i> is unequivocally from the Hettangian but might be present in the Rhaetian to lower Sinemurian. The genus is geographically widespread across the U.K. http://www.zoobank.org/urn:lsid:zoobank.org:pub:23CA73CE-BB9A-4EAD-81BA-A6D27ABC82CB SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: Lomax, D. R., J. A. Massare, and R. T. Mistry. 2017. The taxonomic utility of forefin morphology in Lower Jurassic ichthyosaurs: <i>Protoichthyosaurus</i> and <i>Ichthyosaurus</i>. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1361433.