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Anatomy and Systematics of the Rhomaleosauridae (Sauropterygia: Plesiosauria)

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Anatomy and Systematics of the Rhomaleosauridae (Sauropterygia: Plesiosauria) Anatomy and Systematics of the Rhomaleosauridae (Sauropterygia: Plesiosauria) Adam Stuart Smith BSc (hons) (Portsmouth), MSc (Bristol) A thesis submitted to the National University of Ireland, University College Dublin for the degree of Doctor of Philosophy November 2007 Supervisor: Dr Gareth J. Dyke Head of School: Professor Thomas Bolger School of Biology and Environmental Science University College Dublin Belfield Dublin 4 Ireland i Contents Frontispiece i Contents ii List of figures vi Acknowledgements xviii Declaration xx Abstract xxi Chapter 1. Introduction and objectives………………………………………….. 1 1.1 General introduction 1 1.2 Palaeobiology 4 1.3 Locomotion 7 1.4 Anatomy 10 1.5 Taxonomic diversity 12 1.6 Thesis objectives 14 1.7 Thesis structure 14 Chapter 2 - Historical background………………………………………………... 16 2.1 History of plesiosaurs 16 2.2 Plesiosaur systematics 16 2.3 Pliosauroidea 16 2.4 Rhomaleosauridae – taxon history 20 2.5 Rhomaleosauridae – previous research 24 2.6 Rhomaleosaurus or Thaumatosaurus? 25 Chapter 3 - Material and palaeontological approaches………………………. 27 3.1 Institutional abbreviations 27 3.2 Data collection –general 28 3.3 NMING F8785 Rhomaleosaurus cramptoni 30 3.3.1 History 30 3.3.2 Iconic specimen 33 3.4 NMING 10194 38 3.5 NMING F8749 38 3.6 NMNH R1336, NMING F8780, TCD.22931 Plesiosaurus 41 macrocephalus 3.7 NMING F8771 and TCD.22932 Thalassiodracon hawkinsi 41 3.8 BMNH 49202 45 3.9 BMNH R38525 Archaeonectrus rostratus 45 ii 3.10 BMNH R4853 Rhomaleosaurus thorntoni 45 3.11 BMNH R2028*, R2029*, R1317, R2061*, R2047*, R2027*, 49 R1318, R1319 and R2030* Eurycleidus arcuatus 3.12 BMNH R5488 Macroplata tenuiceps 50 3.13 BMNH R1310, TCD.47762a, TCD.47762b, 51 3.14 YORYM G503 Rhomaleosaurus zetlandicus 51 3.15 WM 851.S Rhomaleosaurus propinquus 54 3.16 SMNS12478 Rhomaleosaurus victor 54 3.17 LEICS G221.1851 54 3.18 WARMS G10875 56 3.19 TCD.57763 Attenborosaurus conybeari 56 3.20 Additional material 56 3.21 Possible rhomaleosaurids excluded from this study 58 Chapter 4 - Specimen descriptions………………………………………………. 59 4.1 Background 59 4.2 NMING F8785, Rhomaleosaurus cramptoni, skull 59 4.2.1 Skull roof 61 4.2.2 Palate 63 4.2.3 Basicranium 65 4.2.4 Mandible 67 4.2.5 Dentition 68 4.3 NMING F8785, Rhomaleosaurus cramptoni, postcranium 70 4.3.1 Axial skeleton 70 4.3.2 Limbs 73 4.3.3 Girdles 76 4.4 BMNH R4853, Rhomaleosaurus thorntoni 78 4.4.1 Axial skeleton 78 4.4.2 Pectoral girdle 93 4.4.3 Pelvic girdle 95 4.4.4 Limbs 97 4.5 YORYM G503, Rhomaleosaurus zetlandicus 100 4.5.1 Forelimb 100 4.5.2 Caudal vertebrae 102 4.6 Rhomaleosaurus full body reconstruction 105 4.7 NMING F10194, skull 108 4.7.1 Skull roof 108 iii 4.7.2 Palate 112 4.7.3 Basicranium 115 4.7.4 Mandible and dentition 117 4.8 NMING F10194, postcranium 117 4.8.1 Axial skeleton 117 4.8.2 Pectoral girdle 118 4.8.3 Pelvic girdle 120 4.8.4 Limbs 120 4.9 NMING F8749 122 4.9.1 Skull roof 122 4.9.2 Palate and dentition 125 4.9.3 Mandible 130 4.10 Comparison of taxa 132 4.10.1 Skull roof comparison 132 4.10.2 Palate comparison 147 4.10.3 Mandible and dentition comparison 148 4.10.4 Axial skeleton comparison 150 4.10.5 Girdles comparison 152 4.10.6 Limbs comparison 153 4.10.7 General proportions comparison 155 Chapter 5 – Morphometric and cladistic analyses…………………………….. 157 5.1 Analyses 157 5.2 Specimen-based morphometric analysis 157 5.2.1 Taphonomy 1 - Preservation of parts 157 5.2.2 Taphonomy 2 – Exposure 157 5.2.3 Accessibility 158 5.2.4 Size of data set 158 5.2.5 Data collection 158 5.2.6 Results 160 5.3 Specimen-based cladistic analysis 160 5.2.1 Character list with character discussion 168 5.3.2 Results 205 Chapter 6 – Systematic palaeontology…………………………………………... 208 6.1 Rhomaleosauridae - Generic and species-level systematics 208 6.1.1 Genus Rhomaleosaurus Seeley, 1874 208 6.1.2 Gen. nov. (for ‘Rhomaleosaurus’ victor) (Fraas, 1910) 208 Tarlo, 1960 iv Tarlo, 1960 6.1.3 Genus Eurycleidus Andrews, 1922a 212 6.1.4 Genus Macroplata Swinton, 1930a 216 6.1.5 Genus Archaeonectrus Novozhilov, 1964 217 6.2 Revised supra-generic systematics 217 Chapter 7 – Discussion…………………………………………………….……… 221 7.1 Phylogenetic analysis – discussion 221 7.2 Plesiosauroid-pliosauroid dichotomy 221 7.3 The base of Pliosauroidea 222 7.4 Leptocleididae, Pliosauridae and Brachauchenidae 222 7.5 Rhomaleosauridae 223 7.6 Eurycleidus 224 7.7 Comparison of Eurycleidus interpretations 226 7.8 Rhomaleosaurus 228 7.9 Simolestes and Maresaurus 229 7.10 Morphometric analysis – discussion 230 7.11 A caudal fin in plesiosaurs? 231 Chapter 8 – Conclusions………………………………………………………….. 233 8.1 Context 233 8.2 Systematics – conclusions 233 8.3. Anatomy – conclusions 235 References……………………………………………………………………………. 237 Appendices…………………………………………………………………………… 257 Appendix 1. Plesiosaur publications 257 Appendix 2. Additional specimens 259 Appendix 3. Abbreviations 268 Appendix 4. Morphometric data 269 Appendix 5. Data matrix 278 v List of figures Figure 1.1. Diagrams of the four main types of temporal organisation in 2 amniote skulls. A. anapsid (no temporal fenestrae), B. synapsid (single lower temporal fenestra), C. diapsid (two temporal fenestrae, upper and lower), D. euryapsid (single upper temporal fenestra). Plesiosaurs possess the euryapsid condition (see text for discussion) (modified from Benton, 1997). Figure 1.2. Cladogram showing the broad-scale interrelationships amongst 2 basal sauropterygians indicating the derived position of Plesiosauria within the clade (arrow) (modified from Rieppel, 2000). Figure 1.3. Life restorations of plesiosaurs. A. a typical plesiosauromorph 5 (Elasmosaurus platyurus), B. a typical pliosauromorph (Liopleurodon ferox). Figure 1.4. Outline of Rhomaleosaurus victor, a plesiosaur from the 8 Posidonia Shale of Germany, exposed in ventral view showing the plate-like girdles, tightly packed gastralia and wing-like limbs, typical of all plesiosaurs (length = 3.44m). Figure 1.5. Variation in plesiosaur skulls and dentition. A. Hydrorion 11 brachypterygius, a plesiosaurid from the Toarcian of Germany (Based on Brown, 1993). B. Kaiwhekea katiki, a cryptoclidid from the Maastrichtian of New Zealand (Redrawn from Cruickshank and Fordyce, 2002). C. Liopleurodon ferox, a pliosaurid from the Callovian of Europe. Redrawn from Noè et al. (2003) (Scale bar = 10cm). Figure 2.1. The first full body reconstruction of a plesiosaur (Plesiosaurus 17 dolichodeirus) (From Conybeare, 1824, Plate XLIX). Figure 2.2. Graph showing the actual and cumulative numbers of plesiosaur 19 species and genera named since the first plesiosaur was introduced in 1821 (see Appendix 1). Each time interval represents two decades; the cumulative numbers of valid genera and species both increase at a steady rate for most of the history, with a noticeable exponential increase in the last two time intervals (1981-today). Data for 2008 – 2020 was estimated based on the average number of new taxa named per year between 2001 and 2007. vi Figure 2.3. Family-level comparison of two competing hypotheses of 21 plesiosaur relationships. The hypotheses are broadly similar, but differ in the position of Polycotylidae. Druckenmiller (2006a) recognises a distinct clade (Leptocleididae) which form a sister relationship with Polycotylidae within Pliosauroidea. O’Keefe (2001a) resolves polycotylids within the Plesiosauroidea. N.B. The Rhomaleosauridae and Cryptoclididae are actually resolved as paraphyletic assemblages in the analysis of Druckenmiller (2006a) but they are depicted here as monophyletic in both cladograms for ease of comparison – for detailed differences between these hypotheses, see Figure 2.4. Figure 2.4. Detailed comparison of two competing hypotheses of 22 relationships amongst plesiosaurs showing major areas of variation (taxa in boxes). The top phylogeny is from Druckenmiller (2006a, modified from Figure 4.42); the bottom phylogeny is from O’Keefe (2001a, modified from Fig. 20). Both phylogenies divide plesiosaurs (labelled ‘PLESIOSAURIA’) into two superfamilies, Plesiosauroidea and Pliosauroidea (Pliosauroidea = Clade A in Druckenmiller’s phylogeny). In particular, note the differing position of polycotylids (=Clade B in Druckenmiller’s phylogeny) in a derived position in Pliosauroidea according to Druckenmiller, and in a derived position in Plesiosauroidea according to O’Keefe. There is also no consensus on the superfamilial affinity of Thalassiodracon. Within Pliosauroidea, the position of Simolestes and Leptocleidus also show significant variation between the phylogenies (see text for further discussion). Figure 3.1. Geographical map showing the discovery locations of twenty-two 29 specimens of Lower Jurassic plesiosaurs, examined during the production of this thesis. All of the specimens originated from the UK and Germany (highlighted in grey). Figure 3.2. Detailed location map of NMING F8785, the holotype of 31 Rhomaleosaurus cramptoni (the area in grey represents the Lias Group). Figure 3.3. Stratigraphic position of NMING F8785, the holotype of 32 Rhomaleosaurus cramptoni. The exact horizon within the Bifrons Zone is unknown (modified from Simms et al. 2004). Figure 3.4 Photograph of specimen NMING F8785, the holotype of 34 Rhomaleosaurus cramptoni, taken prior to the specimen being broken up and moved to storage. vii and moved to storage. Figure 3.5. One of ten blocks containing the postcranium of specimen 35 NMING F8785, the holotype of Rhomaleosaurus cramptoni. As of October 2007, these still await reconstruction and preparation. Figure 3.6. Padded fibreglass case constructed to enclose and protect 35 specimen NMING F8785, the skull of the holotype of Rhomaleosaurus cramptoni. Figure 3.7. Casts of the holotype of Rhomaleosaurus cramptoni on display, 36 A. in the Natural History Museum, London, UK; B. in the Bath Royal Literary and Scientific Institute, Bath, UK. See text for discussion of the differences between these casts. C. (over page) Illustration of “Item No.
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