The taxonomic utility of forefin morphology in Lower Jurassic ichthyosaurs: Protoichthyosaurus and Ichthyosaurus

  • Dean Lomax (Contributor)
  • JUDY A. MASSARE (Contributor)
  • Rashmiben T. Mistry (Contributor)



    <p>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.</p> <p><a href="" target="_blank"></a></p> <p>SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at <a href="" target="_blank"></a></p> <p>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.</p>
    Date made available9 Oct 2017

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