Neoproterozoic Geobiology and Paleobiology

314 Pages·2006·15.759 MB·English

by  Susannah M. Porter (auth.), Shuhai Xiao, Alan J. Kaufman (eds.)

Volume 27 • TOPICS IN GEOBIOLOGY A S
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Series Editors: Neil H. Landman and Douglas S. Jones an u
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J. K ai X
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Neoproterozoic Geobiology m a
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n d Volume 27 • TOPICS IN GEOBIOLOGY • Series Editors: Neil H. Landman and Douglas S. Jones
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and Paleobiology E
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Edited by
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Shuhai Xiao and Alan J. Kaufman
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The Neoproterozoic Era (1000–542 million years ago) has become a major focus
r
of geobiological investigations because it is a geological period characterized by o
dramatic climatic change and important evolutionary innovations. Repeated t
glaciations of unusual magnitude occurred throughout this tumultuous interval, e
and various eukaryotic clades independently achieved multicellularity, becoming r
o
more complex, abundant, and diverse at its termination. Animals made their first
z
debut in the Neoproterozoic too.
o
This volume presents a sample of views and visions among some of the growing i
c
numbers of Neoproterozoic workers. It includes a set of multidisciplinary reviews
G
on the Neoproterozoic fossil record (animals, algae, acritarchs, protists, and trace
fossils), evolutionary developmental biology of animals, molecular clock e
estimates of phylogenetic divergences, and Neoproterozoic chemostratigraphy o
and sedimentary geology. These topics are of continuing interest to geoscientists b
and bioscientists who are intrigued by the deep history of the Earth and its
i
inhabitants. o
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Edited by
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Shuhai Xiao and Alan J. Kaufman
ISBN 978-1-4020-5201-9
❯ 9 781402 052019
springer.com
NEOPROTEROZOIC GEOBIOLOGY AND PALEOBIOLOGY
TOPICS IN GEOBIOLOGY

For detailed information on our books and series please vist: www.springer.com

Series Editors:
Neil H. Landman, American Museum of Natural History, New York, New York, [email protected]
Douglas S. Jones, University of Florida, Gainesville, Florida, [email protected]

Current volumes in this series
V olume 27: Neoproterozoic Geobiology and Paleobio logy
Shuhai Xiao and Alan J. Kaufman
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Gregg F. Gunnell
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Volume 17: The History and Sedimentology of Ancient Reef Systems
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Volume 16: Paleobiogeography
Bruce S. Lieberman
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Neoproterozoic Geobiology
and Paleobiology
Edited by
SHUHAI XIAO
DepartmentofGeosciences,
VirginiaPolytechnicInstituteandStateUniversity,
Blacksburg,VA24061,USA
and
ALAN J. KAUFMAN
DepartmentofGeology,
UniversityofMaryland,
CollegePark,MD20743,USA
AC.I.P.CataloguerecordforthisbookisavailablefromtheLibraryofCongress.
ISBN-101-4020-5201-4(HB)
ISBN-13978-1-4020-5201-9(HB)
ISBN-101-4020-5202-2(e-book)
ISBN-13978-1-4020-5202-6(e-book)
PublishedbySpringer,
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www.springer.com
Printedonacid-freepaper
Coverillustrations:MulticellularalgalfossilsfromtheNeoproterozoicDoushantuoFormationat
Weng’an,GuizhouProvince,SouthChina.
AllphotographscourtesyofDr.XunlaiYuanatNanjingInstituteofGeologyandPaleontology.
AllRightsReserved
©2006Springer
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Aims & Scope Topics in Geobiology Book Series

Topics in Geobiology series treats geobiology–the broad discipline that
covers the history of life on Earth. The series aims for high quality, scholarly volumes
of original research as well as broad reviews. Recent volumes have showcased a
variety of organisms including cephalopods, corals, and rodents. They discuss the
biology of these organisms-their ecology, phylogeny, and mode of life–and in
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Other volumes are more theme based such as predator-prey relationships,
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This is treated in skeletal mineralization and how such skeletons record environmental
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The series editors also welcome any comments or suggestions for future
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v
Dedication

This work is dedicated to Prof. Zhang Yun
(1937-1998), our mentor and friend.

(Photograph by Alan J. Kaufman, 1991)
vii
Preface
The Neoproterozoic Era (1000–542 million years ago) is a geological
period of dramatic climatic change and important evolutionary innovations.
Repeated glaciations of unusual magnitude occurred throughout this
tumultuous interval, and various eukaryotic clades independently achieved
multicellularity, becoming more complex, abundant, and diverse at its
termination. Animals made their first debut in the Neoproterozoic too. The
intricate interaction among these geological and biological events is a
centrepiece of Earth system history, and has been the focus of geobiological
investigations in recent decades. The purpose of this volume is to present a
sample of views and visions among some of the growing numbers of
Neoproterozoic workers.
The contributions represent a cross section of recent insights into the
field of Neoproterozoic geobiology. Chapter One by Porter gives an up-to-
date review of Proterozoic heterotrophic eukaryotes, including fungi and
various protists. Heterotrophs are key players in Phanerozoic ecosystems;
indeed, most Phanerozoic paleontologists work on fossil heterotrophs.
However, the fossil record of Proterozoic heterotrophs is extremely meagre.
Why? Porter believes that preservation is part of the answer. Chapter Two
by Huntley and colleagues explore new methods of quantifying the
morphological disparity of Proterozoic and Cambrian acritarchs, the vast
majority of which are probably autotrophic phytoplankton. They use non-
metric multidimensional scaling and dissimilarity methods to analyze
acritarch morphologies. Their results show that acritarch morphological
disparity appears to increase significantly in the early Mesoproterozoic, with
an ensuing long period of stasis followed by renewed diversification in the
Ediacaran Period that closed the Neoproterozoic Era. This pattern is broadly
consistent with previous compilation of acritarch taxonomic diversity, but
also demonstrates that initial expansion of acritarch morphospace appears to
predate taxonomic diversification. Using similar methods, Xiao and Dong in
Chapter Three analyze the morphological disparity of macroalgal fossils,
which likely represent macroscopic autotrophs in Proterozoic oceans. The
pattern is similar to that of acritarchs: stepwise morphological expansions in
both the early Mesoproterozoic and late Neoproterozoic separated by
prolonged stasis. What might have caused the morphological stasis of both
microscopic and macroscopic autotrophs? The authors speculate that it might
have something to do with nutrient limitation.
ix
x Preface

The following two chapters review the depauperate fossil record of
Neoproterozoic animals, or at least fossils that have been interpreted as
animals. Chapter Four by Bottjer and Clapham places emphasis
particularly on the evolutionary paleoecology of benthic marine biotas in the
Ediacaran Period. They interpret the paleoecology of Ediacaran fossils in
light of increasing evidence of a mat-based world. These authors are
particularly intrigued by the non-random association of certain Ediacara
fossils (e.g., fronds vs. bilaterians) and the contrasting ecological roles
between bilaterian and non-bilaterian tierers in Ediacaran epibenthic
communities. They notice that the Avalon (575–560 Ma) and Nama (549–
542 Ma) assemblages appear to be dominated by non-bilaterian fronds that
stood as tall tierers above the water-sediment interface, while the White Sea
assemblage (560–550 Ma) seems to be characterized by flat-lying Ediacara
organisms, including such forms as Dickinsonia that may be interpreted as
mobile animals. It is still uncertain whethe r a ll o r m ost Ediacara fossils
can be interpreted as animals, but it is clear that evidence of animal activities
is preserved as trace fossils in the last moments of Ediacaran time. Jensen,
Droser, and Gehling take a step further in Chapter Five to comprehensively
review the Ediacaran trace fossil record. The interpretation of Ediacaran
trace fossils is not as straightforward as one would think. Many Ediacaran
body fossils are morphologically simple spheres, discs, tubes, or rods. In
many cases, these simple fossils, particularly when preserved as casts and
molds, mimic the morphology of trace fossils such as tubular burrows or
cnidarian resting traces. Jensen and colleagues do a heroic job of critically
reviewing most published claims of Ediacaran trace fossils. They found that
many Ediacaran trace fossil-like structures lack the diagnostic features (e.g.,
sediment disruption) of animal activities, and may be alternatively
interpreted as body fossils. Thus, although there are bona fide animal traces
in the White Sea and Nama assemblages, they conclude that previous
estimates of Ediacaran trace fossil “diversity” have been unduly inflated.
Developmental and molecular biologists play a distinct role in
understanding animal evolution. In Chapter Six, Erwin takes an evo-devo
approach to reconstruct what the “urbilaterian”—the common ancestor of
protostome and deuterostome animals—would look like. Did it have a
segmented body with anterior-posterior, dorsal-ventral, and left-right
differentiation? Did it have eyes to see the ancient world? Did it have a
through gut system to leave fecal strings in the fossil record? Did it have legs
to make tracks? In principle, one can at least achieve a partial reconstruction
of the urbilaterian bodyplan based on a robust phylogeny and the
phylogenetic distribution of key genetic toolkits. In reality, however, the
presence of genetic toolkits does not guarantee the expression of the
Preface xi

corresponding morphologies, and homologous genetic toolkits can be
recruited to code functionally related, but morphologically distinct and
evolutionarily convergent structures. Fortunately, the absence of certain
critical genetic toolkits means the absence of corresponding morphologies.
Thus, by figuring out what genetic toolkits might have been present in the
urbilaterian, Erwin presents a number of ideas about how complex the
urbilaterian could have possibly been, thus sheding light on a maximally
complex urbilaterian. This is useful for paleontologists who have been
searching for the urbilaterian without a search image, but it does not tell
paleontologists what geological period they should focus on in their search.
Molecular biologists believe that they can fill this gap by comparing
homologous gene sequences of different organisms, based on the assumption
that divergence at the molecular level follows a clock-like model. Hedges
and colleagues present such a molecular timescale in Chapter Seven.
Hedges and colleagues summarize the molecule-derived divergence times of
major clades, including oxygen-generating cyanobacteria and methane-
generating euryarchaeotes that have shaped the Earth’s surface. In addition,
they also present a eukaryote timetree (phylogeny scaled to evolutionary
time) in the Proterozoic and give a critical review of the ever complicated
models and methods devised to account for the stochastic nature of
molecular clocks. Overall, Hedges and colleagues believe that many
eukaryote clades, including animals, fungi, and algae, may have a deep
history in the Mesoproterozoic–early Neoproterozoic. And they found
possible temporal matches between the evolution of geobiologically
important clades (e.g., land plants, fungi, etc.) and geological events (e.g.,
Neoproterozoic ice ages). The field of molecular clock study is still in its
infancy, and one would expect more exciting advancements and
improvements as it matures over the coming decades.
Another way to date evolutionary and geological events is to correlate
relevant strata with geochronometrically constrained rock units. Because
index fossils are rare in the Neoproterozoic Era, chemostratigraphic methods
using stable carbon isotopes, strontium isotopes, and more recently sulfur
isotopes, have been used to correlate Neoproterozoic rocks. In Chapter
Eight, Halverson presents a Neoproterozoic carbon isotope
chemostratigraphic curve based on four well-documented sections. This
curve provides a basis on which he considers several key geobiological
questions in the Neoproterozoic, including the number and duration of
glaciations, and the relationship between widespread ice ages and evolution.
In addition to chemostratigraphic data, some distinct sedimentary features
have also been used in Neoproterozoic stratigraphic correlation. For
example, an enigmatic carbonate is typically found atop Neoproterozoic