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A Taxonomic Review of Ichthyosaurus from Somerset a Thesis Submitted To A taxonomic review of Ichthyosaurus from Somerset A thesis submitted to The University of Manchester for the degree of Master of Philosophy (MPhil) in the Faculty of Engineering and Physical Sciences 2015 Dean R. Lomax School of Earth, Atmospheric and Environmental Sciences TABLE OF CONTENTS TABLE OF CONTENTS ........................................................................................................ 2 LIST OF PRIMARY FIGURES .............................................................................................. 5 APPENDIX A FIGURES ........................................................................................................ 9 APPENDIX B FIGURES ...................................................................................................... 10 ABSTRACT............................................................................................................................ 13 DECLARATION .................................................................................................................... 14 COPYRIGHT STATEMENT ................................................................................................ 14 DEDICATIONS ...................................................................................................................... 15 INSTITUTIONAL ABBREVIATIONS ................................................................................. 16 1. ACKNOWLEDGEMENTS ............................................................................................... 17 2. INTRODUCTION .............................................................................................................. 18 3. MATERIALS AND METHODS ....................................................................................... 20 4. GEOLOGICAL SETTING ................................................................................................ 21 5. A HISTORY OF ICHTHYOSAURUS STUDY WITH EMPHASIS ON SOMERSET .................................................................................................................................................. 24 6. THE TAXONOMIC IMPLICATIONS OF ‘ICHTHYOSAURUS’ SPECIMENS FROM SOMERSET AND THEIR PHYLOGENETIC POSITION ............................................... 31 7. CLADISTIC ANALYSIS .................................................................................................. 33 7.1. RESULTS ................................................................................................................... 35 7.2.1 SPECIES #1 ..................................................................................................... 38 2 7.2.1A. Species characteristics: .................................................................. 38 7.2.1B. Species interpretation: .................................................................... 38 7.2.1C. Specimen description(s):................................................................ 39 7.2.2 SPECIES #2 .................................................................................................... 41 7.2.2A. Species characteristics: .................................................................. 41 7.2.2B. Species interpretation: .................................................................... 41 7.2.2C. Specimen description(s):................................................................ 42 7.2.3 SPECIES #3 (‘CLUSTER 1’) ........................................................................ 43 7.2.3A. Species characteristics: .................................................................. 43 7.2.3B. Species interpretation: .................................................................... 44 7.2.3C. Specimen description(s):................................................................ 45 7.2.4 SPECIES #4 (‘CLUSTER 2’) ........................................................................ 52 7.2.4A. Species definition: ........................................................................... 52 7.2.4B. Species interpretation: .................................................................... 53 7.2.4C. Specimen description(s):................................................................ 54 7.2.5 SPECIES #5? .................................................................................................. 67 7.2.5A. Species questionable: ..................................................................... 67 7.2.5B. Specimen description(s): ................................................................ 68 7.2.6 ADDITIONAL SPECIMENS .......................................................................... 69 7.2.6A. Specimen description(s): ................................................................ 69 8. DISCUSSION .................................................................................................................... 75 8.1. Interpretation of results: .................................................................................... 75 3 8.2. Comparison of the neotype with Ichthyosaurus specimens in Somerset: .............................................................................................................................................. 76 8.3. A cladistic analysis without the neotype: ....................................................... 77 8.4. Ichthyosaurus implications: .............................................................................. 79 9. FUTURE RESEARCH ..................................................................................................... 81 10. SUMMARY AND CONCLUSION ................................................................................ 84 11. REFERENCES................................................................................................................ 85 12. APPENDICES ................................................................................................................. 94 Appendix A: List of characters for cladistic analysis .................................................... 94 Appendix B: Interpretation of character maps with comments regarding the usefulness of characters used ....................................................................................... 109 Appendix C: Individual character coding for the cladistic analysis .......................... 153 Word count, excluding references, appendices and figure explanations: 19,786 4 List of primary figures Figure 1. Artist illustration of a family of Ichthyosaurus swimming in the Early Jurassic seas. Illustration courtesy of James McKay. Figure 2. Map of Somerset with some of the important ichthyosaur-bearing localities mentioned, plus other major locations. Varied topography: slightly shaded areas show upland (Exmoor, Mendips, Quantocks) and horizontal lines indicate lowland (Somerset Levels). Modified from Haslett (2010; Figure. 1.3). Figure 3. The lithostratigraphy and biostratigraphy of the Blue Lias Formation. Reproduced from Ambrose (2001). Figure 4. Illustration (lithograph) of the original I. communis holotype tooth (Conybeare, 1822; Plate 15, Figure. 8) and paratype forefin (Conybeare, 1822; Plate 20, Figure. 1) modified from Conybeare (1822). Figure 5. An early illustration of an ichthyosaur found in 1818 at Watchet, initially identified as a fish. Unfortunately the specimen’s current whereabouts are unknown, although it was apparently purchased by the Royal College of Surgeons. It appears that an identification of Ichthyosaurus is more than appropriate, given the morphology of the forefin. Modified from Delair (1969; Figure. 3). Figure 6. The variation of the matrix ‘enhancements’/differences of several of the samples specimens from this study; some are potentially suggestive of a composite specimen. A. AGC 11: Two different matrix types which suggests the specimen was placed into a different block, plus several distinct cracks run throughout. B. AGC 12: Painted matrix, covering either original matrix or plaster. C. ANSP 17566: Patched matrix (chisel-like markings) and distinct lines (arrow points to a distinct line in the matrix). D. CAMSM J59575: At least four distinct types of ‘matrix’ are present, including the clear use of plaster and a specific type of patchwork. Figure 7. A selection of forefins belonging to specimens of Ichthyosaurus, exemplifying the high degree of variation found within the genus. Ulnare coloured in blue. Modified from Motani (1999a; Figure. 6, the forefins of Ichthyosaurus). Figure 8. The selected tree (cladogram) from the specimen-level cladistic analysis, representing five potentially distinct species of Ichthyosaurus found in the results. Node 16: Species #1; Node 11: Species #2; Node 29: Species #3 (‘Cluster 1’); Node 21: Species #4 (‘Cluster 2’) and Node 5: Species #5?. Figure 9. A representative photograph of the ‘ichthyosaur wall’ in the Fossil Marine Reptiles gallery at the NHMUK. Some of the most complete, and historically 5 important specimens are on display, many are from Somerset. Note the lighting problems for viewing specimens that are positioned high on the wall. Figure 10. The practically complete skeleton of NMW 93.5G.2, the sole representative of Species #1. Scale bar = 10 cm. Figure 11. Close-up of the pelvic and hindfin area of NMW 93.5G.2. IS = Ischia. IL = Ilium. LF = Left femur. RF = Right femur. Scale bar = 2 cm. Figure 12. The nearly complete skeleton of CAMSM J35183, the sole representative of Species #2. Scale bar = 10 cm. Figure 13. The partial skeleton of CAMSM J59575, a specimen encompassed within Species #3 (Cluster 1).
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