Geological Magazine

Original Articles

A Middle Jurassic (Bajocian) ophthalmosaurid (Reptilia, Ichthyosauria) from the Tuxedni Formation, Alaska and the early diversification of the clade

PATRICK S. DRUCKENMILLERa1 c1 and ERIN E. MAXWELLa2

a1 University of Alaska Museum and Department of Geology and Geophysics, University of Alaska Fairbanks, 907 Yukon Dr., Fairbanks, AK 99775

a2 Paläontologisches Institut und Museum, Universität Zürich, Karl-Schmid Strasse 4, 8006 Zürich, Switzerland

Abstract

Ophthalmosauridae is a clade of derived thunniform ichthyosaurs that are best known from Callovian (late Middle Jurassic) to Cenomanian-aged (Late Cretaceous) deposits in both the Northern and Southern Hemispheres. Ophthalmosaurids arose prior to the Early–Middle Jurassic boundary, however, very little is known about their diversity and distribution in the earliest phase of their evolutionary history during the Aalenian–Bathonian (Middle Jurassic) interval. Here we describe new diagnostic ophthalmosaurid material from the Early Bajocian (Middle Jurassic) of Alaska. The specimen, UAMES 3411, is a partial disarticulated skull that was discovered in the Middle Jurassic Tuxedni Formation, which was deposited in shallow marine settings outboard of the then-accreting Wrangellia composite terrane. The new material is significant in that it is the first Jurassic ichthyosaur described from Alaska, one of the oldest ophthalmosaurids known and the only Middle Jurassic ophthalmosaurid described from the Northern Hemisphere. The new material adds to a rapidly growing data set on ophthalmosaurid diversity and suggests that the clade was geographically widespread by the Early Bajocian, very early in its evolutionary history.

(Received December 01 2012)

(Accepted January 21 2013)

(Online publication April 04 2013)

Keywords:

  • Talkeetna Mountains;
  • Ophthalmosaurinae;
  • palaeobiogeography;
  • systematics
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