Ichthyosaurs from the Upper Triassic of the New Siberian Islands, Russian Arctic

The first ichthyosaur specimens discovered from the Upper Triassic of the Russian Arctic (Kotelny Island, New Siberian Islands) are described. They include the remains of large and small-bodied ichthyosaurs originating from six stratigraphic levels spanning the lower Carnian to middle Norian. The material is mostly represented by vertebrae and ribs, which are not possible to accurately diagnose, but also includes associated vertebrae and a fragmentary skeleton that preserves cranial remains (parabasisphenoid, fragmentary quadrate, partial mandible and hyoids). The cranial remains preserved in the specimen ZIN PH 5/250 were studied using computed tomography. Its mandible is highly similar to those of toretocnemids, whereas the parabasisphenoid demonstrates a peculiar combination of both primitive and derived character states, providing the first detailed data on this cranial element in Late Triassic ichthyosaurs. Furthermore, the specimen also demonstrates a distinctive condition of rib articulation in the anterior-most presacral (cervical) vertebrae, and is proposed to represent a new taxon. Although the phylogenetic position of this taxon is uncertain due to its fragmentary nature, its anatomy, indicating toretocnemid or/and parvipelian affinities, further supports the previously hypothesized sister-group relationships between these two clades. [Zverkov N.G., Grigoriev D.V., Wolniewicz A.S., Konstantinov A.G. & Sobolev E.S. Ichthyosaurs from the Upper Triassic (Carnian–Norian) of the New Siberian Islands, Russian Arctic, and their implications for the evolution of the ichthyosaurian basicranium and vertebral column. Earth and Environmental Science Transactions of the Royal Society of Edinburgh (In press) doi:10.1017/S1755691021000372]