Contributions to Exceptional Fossil Preservation Anthony Drew Muscente Dissertation submitted to the faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy In Geosciences Shuhai Xiao Kenneth A. Eriksson Benjamin C. Gill Sterling Nesbitt March 18, 2016 Blacksburg, Virginia Keywords: Geobiology, Paleobiology, Paleontology, Taphonomy Copyright 2016 © A. D. Muscente Contributions to Exceptional Fossil Preservation Anthony Drew Muscente ABSTRACT Exceptionally preserved fossils—or fossils preserved with remains of originally non-biomineralized (i.e. soft) tissues—constitute a key resource for investigating the history of the biosphere. In comparison to fossils of biomineralized skeletal elements, which represent the majority of the fossil record but only a fraction of the total diversity that existed in the past, exceptionally preserved fossils are comparatively rare because soft tissues are rapidly destroyed in typical depositional environments. Assemblages of such fossils, nonetheless, have received special attention among scientists in multiple fields of Earth and life sciences because they represent relatively “complete” windows to past life. Through such windows, researchers are able to reconstruct original biological features (e.g. soft tissue anatomies) of extinct organisms and to describe the structures and compositions of ancient soft-bodied paleocommunities. To accomplish these goals, however, researchers must incorporate background information regarding the pre- and post-burial histories of exceptionally preserved fossils. In this context, my dissertation focuses on the environmental settings, diagenetic conditions, geomicrobiological activities, and weathering processes, which influence the conservation of original biological features within exceptionally preserved fossils and control their occurrences in time and space. An improved understanding of these critical factors involved in exceptional fossil preservation will ultimately our advance our knowledge regarding the history of the biosphere and the Earth system as a whole. Each chapter of original research in this dissertation includes an innovative and distinct approach for studying exceptional fossil preservation. The second chapter describes environmental and geologic overprints in the exceptional fossil record, as revealed by a comprehensive statistical meta-analysis of a global dataset of exceptionally preserved fossil assemblages. Moving from global to specimen-based perspectives, the second and third chapters focus on minerals (products of geomicrobioloigcal, diagenetic, and weathering processes) and carbonaceous materials replicating exceptionally preserved fossils. The third chapter examines the causes of preservational variations observed among organophosphatic tubular shelly Sphenothallus fossils in the lower Cambrian of South China using an experimental approach. (Although Sphenothallus is not an exceptionally preserved fossil sensu stricto, its conservation of original organic matrix tissues in South China provides key insights into the preservation of carbonaceous material within fossils.) Lastly, the fourth chapter presents data acquired using various in situ nanoscale analytical techniques to test the hypothesis that microstructures within exceptionally preserved microfossils of the Ediacaran Doushantuo Formation of South China are some of the oldest putative cylindrical siliceous demosponge spicules in the fossil record. Collectively, these chapters describe environmental, authigenic, diagenetic, and weathering processes that affect exceptional fossil preservation, and highlight innovative methods and approaches for testing major paleobiologic and geobiologic hypotheses regarding exceptionally preserved fossils. DEDICATION I dedicate this work to my mother, father, sister, and girlfriend, who keep me mindful of the past and present, and more importantly, hopeful about the future. iii ACKNOWLEDGEMENTS I wish to thank everyone who has supported my pursuit of education; contributed to my development as a scientist and academic; and played a role in my maturation as a human being. Certainly, no list will ever adequately acknowledge all the help I’ve received through the years. Nonetheless, I’d like to take this opportunity to acknowledge and thank the following exceptional individuals (in no particular order) for their support:  My mother, Donna, who has done more to support my education than anyone else  My father, Anthony, who taught me (by example) that success comes from patience, hard work, and perseverance  My sister, Miranda  My girlfriend, Pilar. I am very thankful we could lean on each other all the way through graduate school.  Pam and Larry Muscente, who gave me my first real jobs, and who visited me more times in Blacksburg than anyone else in my family  My fellow graduate students—particularly those in paleontology, including Mike Meyer, Andrew (Drew 1) Hawkins, Jesse Broce, Ken O’Donnell, Jackie Wittmer, Qing Tang, Natasha Bykova, Caitlin Colleary, Candice Stefanic, and Chris Griffin—for fun conversations, heated (mostly productive) exchanges, constructive feedback, and generally good times  The teachers, professors, and mentors who were instrumental in my education  My PhD committee: Ken Eriksson, Ben Gill, and Sterling Nesbitt  The faculty and staff of the Virginia Tech Institute of Critical Technology and Applied Science (ICTAS) Nanoscale Characterization and Fabrication Laboratory (NCFL), particularly Steve McCartney, Jay Tuggle, and Chris Winkler, who made much of the analytical work in this dissertation possible  My co-authors and collaborators—Marc Michel, James Dale, Jim Schiffbauer, Marc Laflamme, John Huntley, Ken O’Donnell, Jesse Broce, Drew Hawkins, Mike Meyer, and Tom Boag—who contributed to the work in this dissertation  All the faculty and staff in the Virginia Tech Department of Geosciences  Warren Allmon, who introduced me to paleontology, encouraged my pursuit of graduate school when I was an undergraduate student, and has continued to support my professional development  Shuhai Xiao, who has been extremely generous, particularly with his time and expertise, as a research adviser and professional mentor iv ATTRIBUTIONS Chapter Two is in the final stages of preparation for submission to a journal of note (suffice it to say that you’ve heard of the journal before and predicting its acceptance is a crapshoot). The tentative title of the publication is “Environmental and geologic overprints in the exceptional fossil record,” and my co-authors in the manuscript are M. Laflamme, J. Schiffbauer, J. Broce, K. O’Donnell, T. Boag, M. Meyer, A. Hawkins, J. Huntley, and S. Xiao. A. D. Muscente conceived the project, and collected data on exceptionally preserved assemblages throughout the timescale. M. Laflamme, J. Schiffbauer, J. Broce, K. O’Donnell, T. Boag, A. Hawkins, and M. Meyer collected data on assemblages from the Ediacaran, Cambrian, Ordovician and Silurian, Cretaceous, Ediacaran, Permian, and Devonian and Carboniferous systems, respectively. A. D. Muscente conducted statistical analyses based on suggestions from A. Hawkins, J. Huntley, and S. Xiao. A. D. Muscente and S. Xiao developed the manuscript with contributions from M. Laflamme, J. Schiffbauer, T. Boag, J. Broce, and J. Huntley. Chapter three, or “New occurrences of Sphenothallus in the lower Cambrian of South China: Implications for its affinities and taphonomic demineralization of shelly fossils,” was published in Palaeogeography, Palaeoclimatology, Palaeoecology, 2015, volume 437, pages 141–164, by A. D. Muscente and S. Xiao. Both A. D. Muscente and S. Xiao conceived the project and collected the material. A. D. Muscente collected all data, and developed the manuscript with contributions from S. Xiao. Chapter four, or “Assessing the veracity of Precambrian ‘sponge’ fossils using in situ nanoscale analytical techniques” was published in Precambrian Research, 2015, volume 263, 142–156, by A. D. Muscente, F. M. Michel, J. G. Dale, and S. Xiao. S. Xiao, F. M. Michel, and A. D. Muscente conceived the project; A. D. Muscente and S. Xiao collected the material, and prepared and surveyed the fossils using transmitted-light microscopy; A. D. Muscente conducted electron microscopy and energy-dispersive X-ray spectroscopy elemental mapping; S. Xiao and F. M. Michel wrote the proposal for synchrotron beam time; A. D. Muscente, J. G. Dale, and F. M. Michel collected and analyzed the synchrotron data; and A. D. Muscente and S. Xiao developed the manuscript with contributions from F. M. Michel and J. G. Dale. v TABLE OF CONTENTS Abstract……………………………………………………………………………………ii Dedication………………………………………………………………………………...iii Acknowledgements……………………………………………………………………….iv Attributions.……………………………………………………………………………….v Table of Contents…………………………………………………………………………vi List of Figures……………………………………………………………………………..x List of Tables……………………………………………………………………………xiii Grant Information……………………………………………………………………….xiv Chapter 1: OVERVIEW OF EXCEPTIONAL PRESERVATIONAL ENVIRONMENTS AND PROCESSES………………………………………………………………………..1 1.1 Introduction……………………………………………………………………………2 1.2 Summary of research………………………………………………………………….4 1.3 References……………………………………………………………………………..6 Chapter 2: ENVIRONMENTAL AND GEOLOGIC OVERPRINTS IN THE EXCEPTIONAL FOSSIL RECORD……………………………………………………11 2.1 Abstract………………………………………………………………………………12 2.2 Introduction…………………………………………………………………………..13 2.3 Methods………………………………………………………………………………14 2.4 Results………………………………………………………………………………..25 2.5 Discussion and conclusions………………………………………………………….27 2.6 Acknowledgements…………………………………………………………………..29 2.7 Figures and figure captions…………………………………………………………..30 vi 2.8 References……………………………………………………………………………62 Chapter 3: NEW OCCURRENCES OF SPHENOTHALLUS IN THE LOWER CAMBRIAN OF SOUTH CHINA: IMPLICATIONS FOR ITS AFFINITIES AND TAPHONOMIC DEMINERALIZATION OF SHELLY FOSSILS…………………….69 3.1 Abstract………………………………………………………………………………70 3.2 Introduction…………………………………………………………………………..71 3.3 Material and geological background…………………………………………………73 3.4 Methods and fossil preparation………………………………………………………75 3.4.1 Biostratinomy………………………………………………………………75 3.4.2 Electron microscopy and elemental analyses……………………………...75 3.4.3 Taphonomic experiment…………………………………………………...79 3.4.4 Allometric growth analysis………………………………………………...80 3.5 Results………………………………………………………………………………..81 3.5.1 Preservation of Sphenothallus at Heziao…………………………………..81 3.5.2 Preservation of Sphenothallus at Jijiapo…………………………………...83 3.5.3 Preservation of Sphenothallus at Siduping………………………………...85 3.5.4 Taphonomic experimentation……………………………………………...86 3.5.5 Sphenothallus allometry……………………………………………………87 3.6 Discussion……………………………………………………………………………87 3.6.1 Sphenothallus composition and microstructure……………………………88 3.6.2 Biostratinomy………………………………………………………………91 3.6.3 Authigenic mineralization and weathering………………………………...92 3.6.4 Taphonomic experiment and secondary demineralization………………...95 3.6.5 Taphonomic model………………………………………………………...96 vii 3.6.6 Sphenothallus reconstruction and affinities………………………………101 3.7 Conclusions…………………………………………………………………………104 3.8 Acknowledgements…………………………………………………………………105 3.9 Tables and table captions…………………………………………………………...106 3.10 Figures and figure captions………………………………………………………..107 3.11 References…………………………………………………………………………138 Chapter 4: ASSESSING THE VERACTIY OF PRECAMBRIAN ‘SPONGE’ FOSSILS USING IN SITU NANOSCALE ANALYTICAL TECHNIQUES…………………….151 4.1 Abstract……………………………………………………………………………..152 4.2 Introduction…………………………………………………………………………153 4.3 Geological setting…………………………………………………………………..157 4.4 Material and methods……………………………………………………………….158 4.5 Results………………………………………………………………………………161 4.6 Discussion…………………………………………………………………………..164 4.6.1 Origin of the spicule-like microstructures………………………………..164 4.6.2 Taphonomy of the spicule-like microstructures………………………….166 4.6.3 Implications for other purported Precambrian sponges…………………..167 4.6.4 Interpreting the Precambrian dearth of biomineralization sponge fossils..171 4.6.4.1 Biomarkers and molecular clocks………………………………171 4.6.4.2 Independent origins of sponge biomineralization in Cambrian...173 4.6.4.3 Taphonomic megabias………………………………………….174 4.7 Conclusions…………………………………………………………………………178 viii 4.8 Acknowledgements…………………………………………………………………179 4.9 Table and table caption……………………………………………………………..181 4.10 Figures and figure captions………………………………………………………..182 4.11 References…………………………………………………………………………191 Chapter 5: CLOSING THOUGHTS ON EXCEPTIONAL FOSSIL PRESERVATION …………………………………………………………………………………………..207 5.1 Conclusions…………………………………………………………………………208 5.2 References…………………………………………………………………………..210 ix LIST OF FIGURES Chapter 2 Figure 2.1 Exceptionally preserved fossils………………………………………………30 Figure 2.2 Exceptional preservation through time and space………………………..31–32 Figure 2.3 Maps of geographic locations of exceptionally-preserved assemblages in each geologic system………………………………………………………………………33–34 Figure 2.4 Paleolatitude distributions of randomly drawn PBDB collections and exceptionally preserved assemblages for Ediacaran-Neogene geologic systems………..35 Figure 2.5 Latitudinal, longitudinal, and paleolatitudinal distributions………………….36 Figure 2.6 Secondary paleolatitude estimates and ages of 548 exceptionally preserved assemblages………………………………………………………………………………38 Figure 2.7 Cluster counts in 30.5 my duration time bins………………………………...39 Figure 2.8 Cluster counts in 20.33 my duration time bins……………………………….41 Figure 2.9 Marine cluster proportions……………………………………………….43–44 Figure 2.10 Transitional cluster proportions…………………………………………45–46 Figure 2.11 Non-marine cluster proportions………………………………………....47–48 Figure 2.12 Marine/transitional and non-marine cluster counts and proportions based on complete-linkage method………………………………………………………………...49 Figure 2.13 Error of Euclidean distances used in hierarchical clustering………………..51 Figure 2.14 Estimates of the global rock outcrop areas, global rock volumes, and North American surface/subsurface rock areas…………………………………………………52 Figure 2.15 Time bin equality testing………………………………………………..53–54 Figure 2.16 Time domain homogeneity testing……………………………………...55–56 Figure 2.17 Cluster counts and rock areas/volumes……………………………………..57 Figure 2.18 Cluster counts and global rock outcrop areas…………………………...58–59 x