Contributions to Exceptional Fossil Preservation Anthony Drew Muscente Dissertation submitted to ...

225 Pages·2016·9.8 MB·English

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.

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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

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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.

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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

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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
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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

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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

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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