Dwarf elephants on Mediterranean islands: A natural experiment in parallel evolution Volume 1 of 2 by Victoria Louise Herridge Department of Genetics, Evolution and Environment University College London A thesis submitted for the fulfillment of the Degree of Doctor of Philosophy University College London, 2010 1 I, Victoria Louise Herridge, confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. Signed: Date: 2 Abstract Mediterranean dwarf elephants represent some of the most striking examples of phyletic body- size change observed in mammals and are emblematic of the ‘island rule’, where small mammals become larger and large mammals dwarf on islands. The repeated dwarfing of mainland elephant taxa (Palaeoloxodon antiquus and Mammuthus meridionalis) on Mediterranean islands provide a ‘natural experiment’ in parallel evolution, and a unique opportunity to investigate the causes, correlates and mechanisms of island evolution and body-size change. This thesis provides the first pan-Mediterranean study that incorporates taxonomic and allometric approaches to the evolution of dwarf elephants, establishing a framework for the investigation of parallel evolution and key morphological correlates of insular dwarfism. I show that insular dwarfism has evolved independently in Mediterranean elephants at least six times, resulting in at least seven dwarf species. These species group into three, broad size-classes: ‘small- sized’ (P. falconeri, P. cypriotes and M. creticus), ‘medium-sized’ (P. mnaidriensis and P. tiliensis) and ‘large-sized’ (Palaeoloxodon sp. nov. and ‘P. antiquus’ from Crete). Size-shape similarities between independent lineages from the east and central Mediterranean indicate that homoplasy is likely among similar-sized taxa, with implications for the existence of meta-taxa. These homoplasies appear to result from the exploitation of ontogenetic trajectories common to the Elephantidae, underpinning the evolution of small size. Interspecific allometry between dwarf and full-sized species can be seen to result from these common, but grade-shifted ontogenetic trajectories, and this may also be true of broader macroevolutionary trends in the Proboscidea. These size-related grade-shifts suggest that similar, but increasingly extreme, modifications of pre-natal development underpin the evolution of insular dwarfism in elephants. By incorporating research into the morphology and ontogeny of teeth and post-crania in full- sized extant and extinct elephants, this thesis provides new insights into insular dwarfism, elephant systematics and elephant functional morphology and adaptation. 3 Acknowledgements A great number of people offered help and support to me throughout the various stages of this thesis. I am indebted to them all. First, and foremost, I am extremely grateful to my supervisors, Adrian Lister and John Hutchinson, for their unfailing encouragement, sound advice, stimulating discussion and eagle-eyed editorial abilities. A heartfelt thank-you to you both. I relied heavily on the hospitality and assistance of various curators and researchers during my data-collection period. All of them were welcoming, helpful and went above and beyond the call of duty to make my visits both successful and enjoyable. Thank-you to: Andy Currant and Richard Sabin (Natural History Museum, London), Carolina di Patti (Gemellaro Museum, Palermo), Gabriella Mangano and Laura Bonfiglio (University of Messina), Francesco Sciuto (University of Catania), John Borg (Heritage Malta), George Iliopolous (Natural History Museum, Heraklion), George Theodorou (University of Athens), Maria Rita Palombo (University of Rome, La Sapienza), Marylène Patou-Mathis (Institut de Paléontologie Humaine), Reinhard Ziegler (Staatliches Museum für Naturkunde Stuttgart), Oliver Sandrock (Hessisches Landesmuseum, Darmstadt), Oliver Hampe, (Humbolt University, Berlin), Cristiano Dal Sasso (Museo Civico di Storia Naturale), Benedetto Sala (Ferrara University) and Emmanuel Gilissen and Wim Wendelen (Afrika Museum, Tervuren, Belgium). Specific acknowledgements must go to Eelco Rohling (National Oceanographic Centre, Southampton), who took the time to explain the process and constraints of reconstructing eustatic sea- level change from the !18O temperature curve, and then provided the necessary calculations for me to create the figures used in this thesis. Also to Rose Anne Weissel (Marine Geoscience Data System, Columbia University) for dealing with my queries over the source data for Mediterranean Bathymetry in GeoMapApp. Their help enabled me to move beyond the literature data for discussion of dwarf elephant palaeogeography. Svetalana Nikolaeva (International Commission of Zoological Nomenclature) dealt patiently with my queries over various articles of the Zoological Code, and showed me the value of a dispassionate approach to taxonomy. Isabel McMann (Radcliffe Science Library, Oxford University) tracked down the minutes of the British Association meetings from 1862, and went through them on my behalf to see if any record remained of Hugh Falconer’s paper presented on ‘Elephas’ melitensis. Their help was fundamental to the outcome of my taxonomic revision of dwarf elephants. Discussions with Eleanor Weston, William Parr, Charlotte Miller, Marco Ferretti, Kirsty Penkman and Wendy Dirks helped to improve the quality and scope of this thesis. Finally, an enormous thank-you must go to all of my friends and family, but especially to my husband, Adrian Glover. Without his unwavering support – emotional and technical – this thesis would not have been completed. This thesis was funded by grants from: UCL Graduate School, SYNTHSYS (European Union) The Systematics Association, the Linnean Society, the Palaeontological Association, the Palaeontological Society and the Quaternary Research Association. 4 Table of Contents Volume 1 Title Page .............................................................................................................................. 1 Declaration ............................................................................................................................ 2 Abstract ................................................................................................................................. 3 Acknowledgements .............................................................................................................. 4 Table of Contents .................................................................................................................. 5 List of Figures ....................................................................................................................... 9 List of Tables ........................................................................................................................ 12 Chapter 1: Introduction ......................................................................................................... 16 1.1. Dwarf elephants and island biology ......................................................................... 16 1.1.1. One hundred and fifty years of dwarf elephant research ............................ 16 1.1.2. Islands and evolutionary biology ................................................................ 19 1.1.3. The island rule ............................................................................................. 21 1.1.4. Causes of insular body-size change ............................................................ 21 1.1.5. Causes of insular dwarfism in elephants ..................................................... 23 1.1.6. Islands as ‘natural experiments’ .................................................................. 25 1.2. Aims and content of this thesis ................................................................................. 26 Chapter 2: Materials and Methods ........................................................................................ 29 2.1. Fossil and comparative collections .......................................................................... 29 2.2. Data collection protocols ......................................................................................... 32 2.2.1. Teeth ........................................................................................................... 32 2.2.2. Postcrania ................................................................................................... 40 Chapter 3: Palaeogeography and Geochronology ................................................................ 50 3.1. Geographical distribution of Mediterranean dwarf elephants ................................. 51 3.2. Geographic isolation of elephants on islands .......................................................... 52 3.2.1. Eustatic sea-level change ............................................................................ 54 3.2.2. Tectonic activity ......................................................................................... 58 3.3. Dating dwarf elephant fossils and horizons ............................................................. 62 3.3.1. 14C dating .................................................................................................... 62 3.3.2. AAR dating ................................................................................................. 65 3.3.3. ESR dating .................................................................................................