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Plesiosaurs from Svalbard

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Plesiosaurs from Svalbard Plesiosaurs from Svalbard by Bård H. Andreassen Cand. Scient. thesis in palaeontology at Universitetets naturhistoriske museer og botaniske hage Seksjon for geologi, Universitetet i Oslo 2004. Contents Abstract .............................................................................................................................. 2 Introduction......................................................................................................................... 3 The fossil history of the Plesiosauria ................................................................................. 3 Taxonomical history of the Plesiosauria .................................................................. 5 Origin of the Plesiosaurs ........................................................................................ 10 Systematics ............................................................................................................. 13 About adaptation to the sea .............................................................................................. 18 Material and methods........................................................................................................ 23 Historical information regarding the fossil specimen A 27745............................... 23 Description of the specimen PMO A 27745......................................................................27 Systematic paleontology .................................................................................................. 28 Class Reptilia ......................................................................................................... 28 Superorder Sauropterygia (Owen 1860) ...................................................... 28 Infraorder Pistosauroidea (Baur 1887) ............................................... 28 Superfamily Pistosauria (Baur 1887) ........................................ 28 Plesiosauria (Blainville 1835).................................................... 28 Plesiosauroidea (Welles 1943) .................................................. 28 Cryptocleidoidea (Williston 1925)............................................ 28 Gen. et sp. indet. ............................................................... 28 List of material ................................................................................................................. 28 Vertebrae ................................................................................................................. 35 Ribs ......................................................................................................................... 42 Pelvic girdle ............................................................................................................ 44 Limbs ...................................................................................................................... 47 Discussion and systematics .............................................................................................. 52 Taxonomical comparison ....................................................................................... 56 Femur ............................................................................................................ 56 Epipodials ...................................................................................................... 57 Pelvis ............................................................................................................. 57 On how plesiosaurs used their flippers for propulsion.............................................60 Jurassic and Cretaceous marine vertebrate fossils from Svalbard in the collection of the Geological Museum, Oslo ............................................................................................... 62 76-ME 10 ................................................................................................................ 62 76-ME 12 ................................................................................................................ 64 Teeth ....................................................................................................................... 82 Humerus................................................................................................................... 82 Ilium ........................................................................................................................ 83 Summary and conclusions .................................................................................................84 Acknowledgements .......................................................................................................... 86 References ........................................................................................................................ 87 Appendix 1.........................................................................................................................94 Appendix 2 ......................................................................................................................100 Matrix of character scoring ....................................................................................105 Abstract: A re-description and a re-classification is made for the plesiosaur specimen PMO A 27745 previously identified in 1962 as Tricleidus svalbardensis Persson. In all probability the fossil is from the Slottsmøya Member of the Agardhfjellet Formation and was collected at the entrance to Sassenfjorden, Svalbard. Its age is Volgian. Study of the material, in reference to the current taxonomy of the Plesiosauria which acknowledges the Polycotylidae as part of the Plesiosauria, suggests that it may belong to the Tricleidia of the Superfamily Cryptocleidoidea. A cladistic analysis of related taxa places Tricleidus svalbardensis in a close relationship with Polycotylus, Dolichorhynchops and Tricleidus. The distal part of the fossil is preserved, from the pelvic girdle backwards with dorsal, sacral, and caudal vertebrae present, along with two ischia, two pubes and two flippers of which the right is almost complete. Some rib fragments are also preserved. A catalogue has been made of all available Jurassic and Cretaceous marine vertebrate material from Svalbard containing three plesiosaur propodials and epipodials, a plesiosaur ilium, a large ichthyosaurian humerus and a few plesiosaur teeth. 2 Introduction This master thesis describes a Tricleidian plesiosaur collected from the Agardhfjellet Formation on Svalbard in 1931. In 1962 the specimen, comprising the distal half, from the pelvis and back, was briefly described by Per Ove Persson then of the University of Lund in Sweden and designated the holotype of a new species, Tricleidus svalbardensis. Persson (1962) assigned the specimen to this genus based mainly on features of the proximal bones in its hind limbs. However, much has changed since regarding plesiosaur classification and a new thorough examination and description of the material was necessary. In addition to a re-description and re-interpretation of the plesiosaur specimen mentioned above a quick look will be taken on other miscellaneous material from Svalbard, in the collection at the Geological Museum of Oslo. Most of this latter material, with the exception of many solitary vertebrae and phalanges, is beyond recognition. However, a few interesting pieces have been found such as plesiosaur teeth, an almost complete plesiosaur ilium, a plesiosaur propodial with a more or less complete autopodium, and lastly what appears to be a very large ichthyosaurian humerus. I will also discuss aspects of the taxonomic chaos surrounding the Plesiosauria and also look at the functional anatomy of the plesiosaurs. In the latter, features of the plesiosaur body structure, especially those of the flippers, associated with aquatic life will be compared with today’s aquatic air-breathers, the Cetaceans, as well as the ichthyosaurs. The fossil history of the Plesiosauria The order Plesiosauria, meaning “near-lizard”, are not dinosaurs but contemporary sea-reptiles or tetrapods that dominated the Mesozoic seas, especially in the Jurassic and the Cretaceous. The earliest remains of the group are of isolated bones from the Middle Triassic (Anisian) of Germany, but the first complete and articulated specimens comes from the Lower Jurassic of Lyme Regis, Dorset, and the Bristol region of England. De la Beche & Conybeare (1821), created the genus Plesiosauria on the basis of miscellaneous and unidentified material from the Lyme Regis region in England. This reconstruction was criticised at the time because it was based on isolated and disarticulated material. However, in December 1823 in the Lower Lias (Sinemurian) near Lyme Regis, an 18 year old girl Mary Anning (1799-1847), found the first ever complete skeleton of this new reptile group, which confirmed Conybeare’s conclusion about a new species (Torrens 1995; Taylor & Torrens 1987). 3 One year later in 1824, this skeleton provided Conybeare with the material with which he made the first specific description of a plesiosaur, the type species Plesiosaurus dolichodeirus (Conybeare 1824) (Fig. 1). This specimen is housed at the Natural History Museum in London (NHM) and is now recognised as the type species for the genus. Fig. 1: Dorsal view of the holotype Plesiosaurus dolichodeirus, BMNH 22656, from the Lower Jurassic of Dorset, England (from Storrs 1997). Even though the limestones in Lyme Regis in Dorset have produced many of the most important plesiosaur specimens
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