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Basal Ichthyopterygian Remains from the Grippia Bonebed (Early Triassic) of Marmierfjellet, Spitsbergen

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Basal Ichthyopterygian Remains from the Grippia Bonebed (Early Triassic) of Marmierfjellet, Spitsbergen Basal ichthyopterygian remains from the Grippia bonebed (Early Triassic) of Marmierfjellet, Spitsbergen M.Sc. Thesis at the Department of Biosciences and the Natural History Museum, University of Oslo Ole Frederik Roaldset II Basal ichthyopterygian remains from the Grippia bonebed (Early Triassic) of Marmierfjellet, Spitsbergen Ole Frederik Roaldset Master Thesis in Biosciences Paleontology Department of Biosciences Natural History Museum Faculty of Mathematics and Natural Sciences UNIVERSITY OF OSLO April 2017 III © Ole Frederik Roaldset, 2017 Basal ichthyopterygian remains from the Grippia bonebed (Early Triassic) of Marmierfjellet, Spitsbergen This work is published digitally by Digitale utgivelser ved UiO (DUO), and catalogued in BYBSYS All rights reserved. No part of this publication may be reproduced or transmitted, in any form or by any means, without permission. Print by Reprosentralen, University of Oslo IV ACKNOWLEDGEMENTS I am deeply grateful to have had the opportunity of joining the Spitsbergen Mesozoic Research Group, and to have enjoyed an amazing field season on Svalbard. For as long as I can remember I have wanted to be part of a paleontological excavation. To the unique backdrop of Flowerdalen, and with the pleasure of a fantastic expedition crew, the field experience ended up surpassing all expectations. First and foremost, I would like to thank my main supervisor, Jørn H. Hurum, for letting me on to the Triassic project and for providing all the support one could wish for. I also want to thank my co-supervisor, Glenn-Peter Sætre, and all the participants of the 2015 field season: Bjørn Lund, Øyvind Enger, Stig Larsen, Lena Kristiansen, Lene Liebe Delsett, Achim Reisdorf, Christina Pokriefke Ekeheien, Aubrey J. Roberts, Victoria Engelschiøn Nash, Charlotte Sletten Bjorå, and Inghild Halvorsen Økland, as well as May-Liss Knudsen Funke, Janne Bratvold, and Hans Arne Nakrem. Ole Frederik Oslo, April 2017 V CONTENTS ACKNOWLEDGEMENTS…………………………………………………………………V 1. INTRODUCTION………………………………………………………….……….……..0 1.1 The Early Triassic of Svalbard…………………………………………….……………..0 1.2 Basal Ichthyopterygia…………………………………………………………………....1 1.3 Historical review of Grippia……………………………………………………………..5 1.4 This study………………………………………………………………………………...6 1.5 Geological setting………………………………………………………………………...7 1.5.1 Svalbard in the Early Triassic……………………………………………………….….7 1.5.2 The Sassendalen group………………………………………………………....……….8 1.5.3 The Vikinghøgda formation…………………………………………………………….8 1.5.4 The Vendomdalen member……………………………………………………………10 1.5.5 The Grippia niveau……………………………………………………………………10 1.5.6 The Grippia bonebed…...…………………………………………………………….10 2. MATERIAL AND METHODS………………………………………………………….12 2.1 Excavation of the bonebed…………………………………………………………...…12 2.2 Material……………………………………………………………………………….....12 2.3 Field methods…………………………………………………………………………...12 2.4 Laboratory methods……………………………………………………………………..13 2.5 Measurements and descriptive terminology………………………………………….…13 3. DESCRIPTION…………………………………………………………………………..14 3.1 Grippia…………………………………………………………………………………..14 3.2 Cranial elements…………………………………………………………………………15 3.2.1 Mandibular elements………………………………………………………………….15 VI 3.2.2 Maxillae……………………………………………………………………………….17 3.2.3 Palatine………………………………………………………………………………..18 3.2.4 Quadrate……………………………………………………………………...……….19 3.2.5 Basioccipital…………………………………………………………………………...21 3.3 Appendicular skeleton…………………………………………………………………...23 3.3.1 Humeri………………………………………………………………………………....23 3.3.2 Radii and ulnae………………………………………………………………….……..26 3.3.3 Paddle elements………………………………………………………………….….…26 3.4 Axial skeleton……………………………………………………………………...…….29 3.4.1 Costae……………………………………………………………………………...…..29 3.4.2 Cervical vertebrae…………………………………………………………..…………30 3.4.3 Dorsal vertebrae…………………………………………………………….…………31 3.4.4 Caudal vertebrae……………………………………………………………..………..32 3.4.5 Apophyses…………………………………………………………………….………33 4. DISCUSSION....…………………………………………………………………………36 4.1 Articulation of the quadrate…………….………………………………………………36 4.1.1 The ichthyopterygian quadrate……………………………………………………….36 4.1.2 Element PMO X (quadrate)………….…………………………………………….…36 4.1.3 Form and function of quadrates in terrestrial ancestors..……………………………..37 4.2 Outline of the body………………………………………..……………………………37 4.2.1 The basal ichthyopterygian bodyplan……………………..………………………….38 4.2.2 The dorsal vertebral centra of Grippia……………………………………………….38 4.2.3 The distal most caudal centra of Grippia…………………………………………….39 4.3 Size discrepancy and taxonomic certainty……………………………………………..40 5. CONCLUSION…………………………………………………………………………..41 VII 6. REFERENCES………………………………………………………………………..….42 7. APPENDICES……………………………………………………………………………50 7.1 Measurements of cervical centra………….…………………………………………….50 7.2 Measurements of dorsal centra………………………………………………………….52 7.3 Measurements of caudal centra…………………………………………………………65 VIII IX 1. INTRODUCTION 1.1 The Early Triassic of Svalbard Life in the Early Triassic was to a great extent characterized by its preceding extinction event. The Permian Triassic Mass Extinction (PTME) is regarded as the most significant of all extinction events in the history of life on Earth (Erwin 1994, Benton 1995, Wignall and Twitchett 1996, Song et al. 2011, Scheyer et al. 2014, Roopnarine and Angielczyk 2015). It has been estimated to have reduced the number of terrestrial vertebrate taxa by 70 percent, and the number of marine faunal taxa by as much as 90 percent (Elewa 2008, Metcalfe and Isozaki 2009, Yin and Song 2013). The global tectonic activity that led to the forming of the supercontinent Pangea is believed to be the most likely underlying cause for the event (He et al. 2014, Yin and Song 2013). This resulted in the release of high amounts of gases into the atmosphere through volcanic activity, and ultimately to a warmer climate (Yin and Song 2013). The oceans circulation was affected by the increased temperature and eventually led to widespread anoxia in the seas (Sun et al. 2012). The aftermath of the devastating mass extinction opened up for rapid radiation together with novel exploitation of previously occupied niches by surviving taxa (Bardet et al. 2014, Ji et al. 2015). These major constitutional alterations of the biotas make investigation of the paleobiology in the Early Triassic a highly exciting subject. But due to occasional poor preservation and lack of diagnostic material in the fossil record it has proven challenging to map out the evolutionary history of certain clades (Motani et al. 2014, Ji et al. 2015). 0 Figure 1: Map of land masses in the early Triassic. The geographical positioning of Svalbard (study area) in the Boreal Sea is marked by a star. From Nash 2016 (modified from Sun et al. 2012). The archipelago of Svalbard is located in the High Arctic of the Northeastern Atlantic Ocean. It consists of all land masses within the defined area from latitudes 74° - 81° north and longitudes 10° - 35° east, with Spitsbergen, Nordaustlandet and Edgeøya being the three largest islands. In the Early Triassic Svalbard was situated on the northern margin of the supercontinent Pangea, at approximately 42° north (Maxwell and Kear 2013). Here it formed a deep cold water shelf in a larger embayment called the Boreal Sea (Wignall et al. 1998, Dallmann et al. 2015). Fossilized remains of a variety of different marine taxa reside in the outcrops from the Early Triassic on several of the islands of Svalbard. Chondrichthyans and coelacanths, as well as marine tetrapods such as temnospondyls and ichtyopterygians are just some of these vertebrate taxa. 1.2 Basal Ichthyopterygia Ichthyopterygia (Owen 1840) is a clade of marine reptiles that arose in the Early Triassic and came to have a cosmopolitan distribution throughout the Mesozoic (Bardet et al. 2014). The group stayed abundant on a world wide scale until the early Late Cretacious, the Cenomanian- Turonian boundary event (Fischer et al. 2014a). Secondarily aquatic, these pelagic diapsids have ecologically been compared to pinnipeds and especially cetaceans (Kelley and Pyenson 1 2015). Their physiological and anatomical adaptations to a life in the sea from a terrestrial tetrapod bauplan display an array of parallels to the evolutionary history of these groups (Kelley and Pyenson 2015). The definition of Ichthyopterygia by Motani (1999), modified by Ji et al. (2015), stating the last common ancestor of Ichthyosaurus communis Conybeare, 1822, Utatsusaurus hataii Shikama, Kamei & Murata, 1978 and Parvinatator wapitiensis Nicholls & Brinkman, 1995 is here followed. Remains of ichthyopterygians from the Triassic of Svalbard have been collected and described since the late 19th century (Nordenskiöld 1866, Hulke 1873, Dames 1895, Yakowlew 1903). To a much greater extent than the later derived forms, Early Triassic ichthyopterygians retained a variety of traits from their land dwelling ancestors (Massare & Callaway 1990, Motani et al. 2014). A shorter rostrum, a longer neck, more robust axial skeletons and notably more prevalent hind flippers and hip arrangements are often seen in the basal forms (Massare & Callaway 1990, Motani et al. 2014). These traits contribute to the idea of an anguilliform mode of locomotion rather than the thunniform which likely is the situation for the derived forms (Motani 1998). The dentition is another trait which underwent major morphological alterations throughout the Mesozoic. From a heterodont arrangement with teeth set in individual sockets to a dental groove in most derived forms (Massare & Callaway 1990). There is also a greater variation in different
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