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Janusaurus, new ichthyosaur from Upper Jurassic of Spitsbergen in Norway



Ben Creisler
bcreisler@gmail.com


New in PloS ONE:


Aubrey Jane Roberts, Patrick Scott Druckenmiller, Glenn-Peter Saetre &
Jørn Harald Hurum (2014)
A New Upper Jurassic Ophthalmosaurid Ichthyosaur from the Slottsmøya
Member, Agardhfjellet Formation of Central Spitsbergen.
PLoS ONE 9(8): e103152.
doi:10.1371/journal.pone.0103152
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0103152

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.