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Tooth Wear, Microwear and Diet in Elasmobranchs

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Tooth Wear, Microwear and Diet in Elasmobranchs TOOTH WEAR, MICROWEAR AND DIET IN ELASMOBRANCHS Thesis submitted for the degree of Doctor of Philosophy University of Leicester By Laura McLennan Department of Geology University of Leicester March 2017 Tooth Wear, Microwear and Diet in Elasmobranchs Laura McLennan As abundant and widespread apex predators, elasmobranchs play influential roles in the food-web dynamics of marine communities. This has obvious implications for fisheries management and marine conservation. For successful conservation, the ecology of a species must be known. An understanding of extinct species ecology is also useful. Unfortunately, diet a key component of a species’ ecology, is relatively understudied in elasmobranchs. For a majority of elasmobranch species, little or no quantitative dietary data exists. This reflects the limitations of current dietary defining methods. This thesis presents two alternative methods that can be used to determine the diet of extinct and extant elasmobranchs: meso-style wear analysis and 3D tooth microtextural analysis. These wear techniques can be applied to small sample sizes, and sampled animals with no stomach contents, thus reducing the impact of study on wild elasmobranch populations. The techniques can also be applied to dried and fossil samples, further reducing the impact of study on wild populations and providing a means for the study of extinct species. Furthermore, these wear techniques provide additional advantages over the traditional methods of stomach contents analysis and observation. The wear, measured through the methods outlined in this thesis, accumulates over a longer timescale. The “snapshot bias” associated with traditional methods is thus overcome when analysing diet via meso-style analyses or 3D microtextural analyses. This thesis also investigates the impact of sediment abrasion to 3D tooth microtextures. Results show that care needs to be taken when comparing fossil specimens originating from deposits with differing sediment compositions. These findings are applicable to any study using 3D microtextural techniques on fossil specimens of any species, as all have been exposed to sediment abrasion before fossilisation. This is the first time that these alternative wear methods have been applied to elasmobranchs. They have displayed the potential to be a powerful tool for the dietary analysis of living and extinct elasmobranchs in the future. i Acknowledgements I would like to start by thanking my supervisor Mark Purnell for his continued patience and advice throughout the duration of my PhD. Without his supervision and insight this PhD would not have been completed. I also thank Mark for the monetary contributions to help me attend conferences and purchase equipment. I would also like to thank the Palaeobiology group at Leicester University for their continued support and ideas throughout this PhD. I would secondly like to thank all persons and institutions (David Ward; Gordon Hubbell; Deep Sea World, Edinburgh; Sea Life, London; American Museum of Natural History, Florida Museum of Natural History) that have provided samples for use in this study, without your kindness and generosity this project would not have got off the ground. I am grateful to those persons and institutions that granted me access to materials which were ultimately not used in this thesis (David Powter and Sedgwick Museum, Cambridge). Chapter 5 would not have been possible without the funding provided by the Palaeontological Association Sylvester Bradley award scheme. I would like to thank those people who provided me with work, to help fund this PhD. You gave me a chance to better myself thank you. Within this I would particularly like to acknowledge Alex and Moira Mosley-Brown, Jan Zalasiewicz, Sarah Lee and The Interdisciplinary sciences team at Leicester University. I wish to acknowledge the Geoscience teaching team at Derby University, whose kindness, support and understanding has got me through the last few months. And finally I would like to thank my friends and family who have had to read drafts of this thesis, listen to endless witterings about sharks and support me when I never thought I would finish. ii Contents List of Tables ...................................................................................................... vi List of Figures ..................................................................................................... ix List of Abbreviations…………………………………………………………………..x 1.0 Introduction .................................................................................................... - 1 - 1.1 Aims and objectives .......................................................................... - 2 - 1.2 Background literature............................................................................ - 3 - 1.2.1 Classic methods of dietary discrimination in elasmobranchs .......... - 3 - 1.2.2 Alternative methods of dietary discrimination ................................. - 7 - 1.2.3 Summary ...................................................................................... - 12 - 2.0 Meso-style wear as a tool for dietary discrimination in elasmobranchs . - 14 - 2.1 Introduction ......................................................................................... - 14 - 2.2 Materials and methods........................................................................ - 17 - 2.2.1 Materials and sampling strategy ................................................... - 17 - 2.2.2 Meso-style wear data acquisition.................................................. - 18 - 2.2.3 Statistical analysis ........................................................................ - 20 - 2.3 Results................................................................................................ - 24 - 2.4 Discussion .......................................................................................... - 40 - 3.1 Introduction ......................................................................................... - 42 - 2.5 Conclusions ........................................................................................ - 45 - 3.0 Microtextural analysis as a tool for dietary discrimination in elasmobranchs.. ..................................................................................................................... - 46 - 3.2 Materials and methods........................................................................ - 46 - 3.2.1 Materials and sampling strategy ................................................... - 46 - 3.2.2 Surface texture data acquisition ................................................... - 49 - 3.2.3 Statistical analysis ........................................................................ - 49 - 3.3 Results................................................................................................ - 50 - 3.4 Discussion .......................................................................................... - 55 - 3.5 Conclusions ........................................................................................ - 57 - 4.0 Taphonomic impacts of sediment abrasion on tooth surface microtextures… ..................................................................................................................... - 58 - 4.1 Introduction ......................................................................................... - 58 - 4.2. Materials and methods....................................................................... - 61 - iii 4.2.1 Materials and sampling strategy ................................................... - 61 - 4.2.2 Surface texture data acquisition ................................................... - 64 - 4.2.3 Statistical analysis ........................................................................ - 65 - 4.3 Results................................................................................................ - 66 - 4.3.1 Does sediment abrasion significantly alter tooth microtextural signals through time?......................................................................................... - 66 - 4.3.2 Does sediment abrasion create false dietary signals on previously unworn tooth surfaces? ......................................................................... - 73 - 4.3.3 Does sediment abrasion remove or modify dietary signals defined by tooth surface microtextures? ................................................................. - 73 - 4.4 Discussion .......................................................................................... - 93 - 4.5 Conclusions ........................................................................................ - 97 - 5.0 Microtextural analysis as a tool for dietary discrimination in the fossil record- Did Carcharodon carcharias cause the extinction of Carcharocles megalodon? ................................................................................................................... ..- 99 - 5.1 Introduction ......................................................................................... - 99 - 5.2 Materials and methods...................................................................... - 104 - 5.2.1 Materials and sampling strategy ................................................. - 104 - 5.2.2 Surface texture data acquisition ................................................. - 113 - 5.2.3 Statistical analysis ...................................................................... - 113 - 5.3 Results.............................................................................................
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