MULTIBRANCHED RANGEOMORPHS FROM THE EDIACARAN MISTAKEN POINT ASSEMBLAGE, NEWFOUNDLAND, CANADA by Emily Louise Bamforth A thesis submitted to the Department of Geological Sciences and Geological Engineering In conformity with the requirements for the degree of Master of Science Queen’s University Kingston, Ontario, Canada (July, 2008) Copyright ©Emily Louise Bamforth, 2008 Abstract Rangeomorphs are a distinct group of millimeter- to meter-scale soft-bodied macrofossils that are restricted to the latter half of the late Neoproterozoic Ediacaran Period (635Ma- 542Ma). These fossils represent an extinct higher level taxon characterized by a modular construction based on a single architectural unit: the centimeter-scale, chevron-shaped rangeomorph element which displays several orders of self-similar branching. These elements could be arranged in a variety of different ways, constituting the wide array of gross morphologies found within the Group Rangeomorpha. The largest and most diverse assemblage of rangeomorph fossils in the world is found at Mistaken Point, on the Avalon Peninsula of Newfoundland, Canada, where these organisms are preserved within their original, in situ paleocommunities. Multibranched rangeomorphs are typified by bush-, comb- and network-shaped fossils which display multiple rangeomorph-bearing structures attached to an untethered basal stolon or central attachment point. Multibranched, comb-shaped rangeomorphs are endemic to Mistaken Point, and are represented by fossils displaying multiple parallel struts emerging along one side of an elongate, curved pedicle rod. Morphological and taphonomic evidence suggests that, in life, this organism had two rows of struts, each bearing a rangeomorph frondlet, arranged in an alternating pattern along the curved, tubular pedicle rod. Biometric analyses imply that the struts were added to both ends of the pedicle rod throughout the organism’s lifetime, with later inflation of the rangeomorph frondlets. Each comb-shaped rangeomorph locality likely represents a different age cohort within the organism’s lifecycle, providing rare evidence for spatfall reproduction in Ediacarans, which is similar to that found in modern macrobenthic organisms with pelagic larvae. ii Network-shaped multibranched rangeomorphs, represented by symmetrical to asymmetrical net- like fossils, are also endemic to Mistaken Point. This genus is reconstructed as having a symmetrical arrangement of flexible, rangeomorph-bearing leaflets that were, in part, neutrally buoyant with respect to the seawater. This flexible leaflet structure is unique, and shared only with a rare, previously undescribed, Ediacaran frond-like organism. It is suggested that the enigmatic leaflet structures shared by these two morphologically distinct taxa represent a new type of rangeomorph branching architecture, and therefore constitute a new type of rangeomorph. iii Statement of Co-Authorship While this thesis is substantially my own work, my supervisor and colleagues have actively contributed to its development. A modification of Chapter 2 is published in the Journal of Paleontology (Bamforth et al. 2008), and is co-authored by Guy M. Narbonne, who helped greatly in the development and editing of the manuscript, and by Michael M. Anderson, who collected the type specimens. Chapter 3 is in preparation for submission to an international journal, and will also be co-authored by Guy M. Narbonne. Taxonomic Statement The systematic paleontology of the three new Ediacaran genera and species described in this thesis does not constitute the official description of these taxa in accordance with the International Code of Zoological Nomenclature (third edition). Chapter 2 is a modification of the paper officially describing Pectinifrons abyssalis, which is published in the Journal of Paleontology (Bamforth et al. 2008). The official descriptions of a Hapsidophyllas flexibilis and Frondophyllas grandis will appear in a modified version of Chapter 3, which is currently being prepared for submission to an international journal. iv Acknowledgements I would like to extend my profound thanks to my supervisor, Guy Narbonne, for his scientific guidance, patient tutelage, and endless enthusiasm for this project and for all of my scholarly pursuits. Guy’s contributions to my development as an academic are numerous and invaluable, but above all, his encouragement to propose, pursue and defend my scientific theories and ideas has given me confidence in myself and in my work that will last a lifetime. A debt of gratitude is also owed to Marc Laflamme for his outstanding mentorship throughout my time at Queens. His advice, and the hours he spent with me in patient explanations and insightful discussions, has significantly improved many aspects of this thesis. Lija Flude has been a valuable colleague and comrade for the past three years. Fieldwork on the Avalon was made more pleasant by her cheerful assistance and her excellent navigational skills along the fog-obscured, moose-infested, flat-tire-inducing back roads of Newfoundland. Fieldwork in the Mistaken Point Ecological Reserve was carried out under scientific permits granted by the Parks and Natural Areas Division, Government of Newfoundland and Labrador. Thanks are also due to the kind and courageous people of Portugal Cove South, Trepassey and Spaniard’s Bay for their hospitality and their constant vigilance and protection of their fossil heritage. This research was generously funded by Queen’s Graduate Awards and an Ontario Graduate Scholarship, in addition to the support granted by the Natural Sciences and Engineering Research Council to my supervisor, Guy Narbonne. Special thanks are extended to Noel James and Bob Dalrymple for patiently providing me with the ‘crash courses’ in geology required when I arrived in Queen’s geology department with a v biology degree- I learned very quickly that even rocks without fossils in them could be exciting. I would additionally like to express my gratitude to Mike Caldwell, my undergraduate supervisor, and Brian Chatterton from the University of Alberta for their guidance and assistance in my paleontological pursuits as an undergrad. I must also offer my sincerest thanks to my friends, my family, and especially to my sister Lucy, for never failing to provide me with cheerful optimism, comic relief, and a sympathetic ear when I needed it. This thesis is dedicated to my parents, Fiona and Stephen, without whose endless, loving support, my childhood dream of becoming a paleontologist would have remained only a dream. For this and for so much more, I can only offer my most sincere, heartfelt thanks. vi Table of Contents Abstract............................................................................................................................................ii Statement of Co-Authorship ...........................................................................................................iv Taxonomic Statement .................................................................................................................iv Acknowledgements..........................................................................................................................v Table of Contents...........................................................................................................................vii List of Figures.................................................................................................................................ix List of Tables ...................................................................................................................................x Chapter 1 General Introduction .......................................................................................................1 1.1 The Ediacara Biota.................................................................................................................1 1.1.1 The Ediacara Biota in Time and Space...........................................................................1 1.1.2 The Mistaken Point Assemblage.....................................................................................3 1.1.3 Reconstructing Rangeomorphs: Taxonomy and Structure ...........................................10 1.2 General Geology ..................................................................................................................12 1.3 Purpose of Thesis.................................................................................................................15 Chapter 2 Growth and ecology of a new multibranched rangeomorph from the Ediacaran Mistaken Point assemblage, Newfoundland, Canada ....................................................................17 2.1 Abstract................................................................................................................................17 2.2 Introduction..........................................................................................................................17 2.3 Geological and Stratigraphic Setting ...................................................................................19 2.4 Systematic Paleontology......................................................................................................26 2.5 Taphonomy and Structure....................................................................................................33 2.6 Growth and Morphology......................................................................................................46