Taxonomy, palaeobiogeography and relationships of cryptoclidid plesiosaurs from the Slottsmøya Member, Agardhfjellet Formation, central Spitsbergen

Abstract

The Late Jurassic – Early Cretaceous marine reptiles of the Boreal Region, have been understudied due to limited access and poor preservation of material. Large-scale excavations in the Late Jurassic – earliest Cretaceous Slottsmøya Member of the Agardhfjellet Formation (central Spitsbergen), have resulted in the description of the first Mesozoic marine reptile Lagerstätte from the Boreal Region. Novel excavation and preparation techniques have been developed to tackle the preservation in permafrost and Arctic settings, which are documented for the first time in this work. Among the 58 collected individuals of ichthyosaurians and plesiosaurians, numerous cryptoclidid plesiosaurs are present. Cryptoclididae is a species rich clade of Middle Jurassic – Early Cretaceous long-necked plesiosaurians best known from the mid- to high-latitude regions of the Northern Hemisphere. The primary aims of this study are to describe and interpret two exceptionally preserved cryptoclidid specimens from the Slottsmøya Member. Analysis of the first specimen enabled a taxonomic clarification of Colymbosaurus. The second specimen is recognised as a new genus and species that preserves, for the first time, cranial material of a Late Jurassic cryptoclidid and is described with the aid of computed tomography. Phylogenetic work includes the addition of new phylogenetic characters, as well as numerous changes to the character states for individual taxa. The resulting phylogenetic trees, provides a new interpretation of the intrarelationships of the Cryptoclididae. This phylogenetic work along with comparable work performed on ophthalmosaurid ichthyosaurs, in conjunction with palaeobiogeographic methods to further our understanding of marine reptile distributions and diversity in the Boreal Region. The results from this study, presents a complex relationship with the distributional patterns of these animals through seaways, being in part, dependent on changes in eustatic sea level and tectonic development of the Northeast Atlantic.

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ORCID for Ian Harding: orcid.org/0000-0003-4281-0581

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