Abstract
Abundant new ichthyosaur material has recently been documented in the Slottsmøya Member of the Agardhfjellet Formation from the Svalbard archipelago of Norway. Here we describe a partial skeleton of a new taxon, Janusaurus lundi, that includes much of the skull and representative portions of the postcranium. The new taxon is diagnosed by a suite of cranial character states including a very gracile stapedial shaft, the presence of a dorsal process on the prearticular and autapomorphic postcranial features such as the presence of an interclavicular trough and a conspicuous anterodorsal process of the ilium. The peculiar morphology of the ilia indicates a previously unrecognized degree of morphological variation in the pelvic girdle of ophthalmosaurids. We also present a large species level phylogenetic analysis of ophthalmosaurids including new and undescribed ichthyosaur material from the Upper Jurassic of Svalbard. Our results recover all Svalbard taxa in a single unresolved polytomy nested within Ophthalmosaurinae, which considerably increases the taxonomic composition of this clade. The paleobiogeographical implications of this result suggest the presence of a single clade of Boreal ophthalmosaurid ichthyosaurs that existed during the latest Jurassic, a pattern also reflected in the high degree of endemicity among some Boreal invertebrates, particularly ammonoids. Recent and ongoing descriptions of marine reptiles from the Slottsmøya Member Lagerstätte provide important new data to test hypotheses of marine amniote faunal turnover at the Jurassic-Cretaceous boundary.
Highlights
From 2004–2012, eight seasons of fieldwork in the Late Jurassic to earliest Cretaceous Slottsmøya Member of the Agardhfjellet Formation in the central Spitsbergen Sassenfjord area, have yielded numerous skeletal remains of marine amniotes (Figure 1) [1,2]
Through a number of papers, these Arctic localities have been documented [3,4,5,6,7,8,9,10,11,12,13,14], which built the framework for what is known as the Slottsmøya Member Lagerstatte (SML), which resulted in the description of two new ophthalmosaurid ichthyosaur taxa; Cryopterygius kristiansenae and Palvennia hoybergeti [15], as well as five new plesiosaurians [16,17,18,19]
We present a description of a third new ophthalmosaurid taxon from the Slottsmøya Member, which includes most of the skull, girdle elements and fore- and hind limbs
Summary
From 2004–2012, eight seasons of fieldwork in the Late Jurassic to earliest Cretaceous Slottsmøya Member of the Agardhfjellet Formation in the central Spitsbergen Sassenfjord area, have yielded numerous skeletal remains of marine amniotes (Figure 1) [1,2]. We present a description of a third new ophthalmosaurid taxon from the Slottsmøya Member, which includes most of the skull, girdle elements and fore- and hind limbs. The specimen, PMO 222.654, is significant in that it represents one of the stratigraphically oldest specimens excavated from the Slottsmøya Member and provides important new morphological data for comparisons with age pene-contemporaneous material from the Kimmeridge Clay Formation of the U.K. and elsewhere. The SML assemblage is significant in being one of only two major marine amniote sites that span the Jurassic-Cretaceous boundary (the other being the Vaca Muerta Formation of Argentina [21,22]), thereby contributing to ongoing discussions regarding potential marine reptile turnover at the Jurassic-Cretaceous boundary [23]
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