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Druckenmiller P.S.,University of Alaska Fairbanks | Knutsen E.M.,University of Oslo | Knutsen E.M.,Haoma Mining NL
Norsk Geologisk Tidsskrift | Year: 2012

Plesiosaurian relationships have been subject to considerable debate at both higher and lower levels within the clade. Recent fieldwork in the Uppermost Jurassic of the Agardhfjellet Formation on central Spitsbergen has uncovered numerous ichthyosaurians and plesiosaurian remains, including three new plesiosauroids, one new pliosauroid referrable to Pliosaurus, and a previously described, re-classified taxon. The phylogenetic relationships of these five taxa were investigated based on data sets previously constructed for global plesiosaurian relationships. Two specimens from the British Kimmeridge Clay Formation and a Russian Volgian (uppermost Jurassic) taxon referrable to Pliosaurus were added to the data matrix to improve the phylogenetic resolution of this genus. The results yielded a tree topology closely conforming to the traditional plesiosauroid and pliosauroid dichotomy, nesting Leptocleidia within the latter. Pliosaurus forms a monophyletic clade containing all currently recognised species. The three new long-necked taxa form a monophyletic sister group to the Cretaceous Elasmosauridae. These results should, however, be considered preliminary pending the discovery of more complete cranial material and adult specimens.


Knutsen E.M.,University of Oslo | Knutsen E.M.,Haoma Mining NL | Druckenmiller P.S.,University of Alaska Fairbanks | Hurum J.H.,University of Oslo
Norsk Geologisk Tidsskrift | Year: 2012

At present, very little is known regarding the diversity and morphological disparity of long-necked plesiosaurs in Tithonian-aged (latest Jurassic) units globally. Here, we describe two species of a new, long-necked plesiosaur genus Spitrasaurus from the Upper Jurassic Slottsmøya Member of the Agardhfjellet Formation on Svalbard. The holotype species of the genus, S. wensaasi, is the most complete long-necked specimen found in this unit to date and is readily diagnosed on the basis of having at least 60 cervical vertebrae possessing a prominent lateral longitudinal ridge, as well as the presence of a column of well-developed preaxial accessory ossicles in the limbs. A second taxon, S. larseni, includes a partial skull that broadly resemblesthe Kimmeridgian taxon Kimmerosaurus, but differs in the morphology of its basioccipital, and in having a distinctive lower jaw with a greatlyelongate and strongly dorsally inflected retroarticular process, among other characteristics. Each species of Spitrasaurus can be differentiated on the basis of cervical vertebral proportions and in the morphology of the cervical ribs, rib facets and neural arches, in addition to being stratigraphically separated. The high number of cervical vertebrae in Spitrasaurus significantly exceeds that for described Middle to Late Jurassic plesiosaurs, but is comparable to some Cretaceous elasmosaurids. The Middle Volgian age of this material helps to bridge the temporal and morphologicalgap between better known Middle and Late Jurassic plesiosaurians from Europe and Late Cretaceous taxa primarily known from North America.


Knutsen E.M.,University of Oslo | Knutsen E.M.,Haoma Mining NL | Druckenmiller P.S.,University of Alaska Fairbanks | Hurum J.H.,University of Oslo
Norsk Geologisk Tidsskrift | Year: 2012

At present, our knowledge of plesiosauroid diversity from the uppermost Jurassic (Tithonian/Volgian) is very limited. Newly discovered material from the Slottsmøya Member of the Agardhfjellet Formation of central Spitsbergen, Svalbard, contributes significant new information on this poorly known interval and helps bridge a temporal gap between better known plesiosaurians from the older Jurassic deposits of Europe, and Cretaceous of North America. The partially articulated skeleton of a juvenile long-necked plesiosaurian, PMO 216.839, is one of the most complete plesiosaur fossils known from Spitsbergen and represents a new taxon, Djupedalia engeri gen. et sp. nov. Whilst sharing some similarities with previously described taxa from the Oxford Clay (Muraenosaurus, Tricleidus, and Cryptoclidus) and the Kimmeridge Clay formations (Kimmerosaurus) of England, the new taxon can be diagnosed by features of the cervical vertebrae, including centrum proportions and morphology, a very pronounced posterior shift in the neural spines relative to the centrum, fused prezygapophyses and greatly elongated postzygapophyses, as well as extremely short dorsal neural spines and femora that are longer than the humeri. The new taxon can also be distinguished from other newly-described plesiosauroids from Svalbard, thus indicating that several plesiosaurian taxa existed at high paleolatitudes during the Late Jurassic.


Knutsen E.M.,University of Oslo | Knutsen E.M.,Haoma Mining NL | Druckenmiller P.S.,University of Alaska Fairbanks | Hurum J.H.,University of Oslo
Norsk Geologisk Tidsskrift | Year: 2012

A partial postcranial plesiosaurian skeleton uncovered on Svalbard in the winter of 1930- 1 was described and named Tricleidus svalbardensis Persson, 1962. However, the precise geographic location and stratigraphic unit in which the skeleton was found were not published. Recent fieldwork on Svalbard has uncovered two more plesiosaur skeletons that are demonstrated herein to be conspecific with the 1931 taxon. These new specimens, along with recently discovered historic documents produced by the excavation members of the 1930-31 expedition, reveal that the holotype specimen, PMO A 27745, was recovered from the Upper Jurassic SlottsmØ.ya Member of the Agardhfjellet Formation, which is Middle Volgian in age. Collectively, the Svalbard material is neither morphologically nor stratigraphically consistent with the Callovian taxon Tricleidus Andrews, 1909 and is here referred to Colymbosaurus Seeley, 1874 from the Kimmeridge Clay Formation (Kimmeridgian to Tithonian) of the UK.

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