Amphibian Evolution: The Life of Early Land Vertebrates

294 Pages·2014·25.63 MB·English

by  Rainer R. Schoch

Topics in Paleobiology
This book focuses on the fi rst vertebrates to conquer the land, and on their long journey to become fully
independent of the water. It traces the origin of tetrapod features and explains how they evolved into
organs suited to a terrestrial life. The major part of the story covers events that occurred up to 370 million
Amphibian
years ago, and necessarily deals with many fossils, but the text is by no means restricted to paleontology.
The book presents a comprehensive picture of amphibian evolution, focusing on several major questions in
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current paleobiology. How diverse were the early tetrapods? In what environments did they live, and how
c
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did they come to be preserved? What do we know about the soft bodies of extinct amphibians, and what
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does that knowledge tell us about the evolution of crucial organs during the transition to land? How did c
h Evolution
early amphibians develop and grow, and what were the major factors in their evolution?
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The Topics in Paleobiology Series is published in collaboration with the Palaeontological Association, m
and is edited by Professor Mike Benton, University of Bristol.
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The Life of Early Land Vertebrates
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Rainer Schoch was born in 1970 in Ludwigshafen, Germany. He is a graduate of the University of b
Tübingen, has undertaken fi eld work in Argentina and the USA, and has worked as a curator and assistant i
a
Rainer R. Schoch
professor at Humboldt University, Berlin. Since 2003 he has been the curator of amphibians and reptiles at
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the Natural History Museum of Stuttgart, Germany.

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Cover image: Stem-amphibian fossil. Skeleton of temnospondyl Sclerocephalus (Pennsylvanian, Germany). Courtesy of Rainer R. Schoch.
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Cover design by Design Deluxe o
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Series Editor: Professor Michael J. Benton

Amphibian Evolution
Books in the Topics in Paleobiology series will feature key fossil groups, key events, and analytical
methods, with emphasis on paleobiology, large-scale macroevolutionary studies, and the latest
phylogenetic debates.
The books will provide a summary of the current state of knowledge and a trusted route into the primary
literature, and will act as pointers for future directions for research. As well as volumes on individual
groups, the Series will also deal with topics that have a cross-cutting relevance, such as the evolution
of significant ecosystems, particular key times and events in the history of life, climate change, and the
application of new techniques such as molecular paleontology.
The books are written by leading international experts and will be pitched at a level suitable for advanced
undergraduates, postgraduates, and researchers in both the paleontological and biological sciences.
The Series Editor is Mike Benton, Professor of Vertebrate Palaeontology in the School of Earth Sciences,
University of Bristol.
The Series is a joint venture with the Palaeontological Association.
Previously published
Dinosaur Paleobiology
Stephen L. Brusatte
ISBN: 978-0-470-65658-7 Paperback; April 2012
Amphibian
Evolution
The Life of Early
Land Vertebrates
Rainer R. Schoch
This edition first published 2014 © 2014 by Rainer R. Schoch
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Library of Congress Cataloging-in-Publication Data
Schoch, Rainer, 1970- author.
Amphibian evolution : the life of early land vertebrates / Rainer R. Schoch.
pages cm
Includes bibliographical references and index.
ISBN 978-0-470-67177-1 (cloth) – ISBN 978-0-470-67178-8 (pbk.) 1. Amphibians, Fossil.
2. Paleobiology. 3. Amphibians–Evolution. I. Title.
QE867.S36 2014
567′.8–dc23
2013039743
A catalogue record for this book is available from the British Library.
Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be
available in electronic books.
Cover image: Stem-amphibian fossil. Skeleton of temnospondyl Sclerocephalus (Pennsylvanian, Germany).
Courtesy of Rainer R. Schoch.
Cover design by Design Deluxe
Set in 9/11.5pt Trump Mediaeval by SPi Publishers, Pondicherry, India
1 2014
Contents
Preface viii
Acknowledgments x
1 Introduction 1
1.1 Changing paradigms in amphibian evolution 3
1.2 Paleobiology: data, methods, and time scales 5
1.3 Concepts and metaphors: how scientists “figure out” problems 7
1.4 Characters and phylogenies 8
1.5 What’s in a name? 8
References 11
2 The Amphibian World: Now and Then 13
2.1 Tetrapoda 14
2.1.1 The tetrapod skeleton 14
2.1.2 Tetrapod characters 23
2.1.3 Stem-tetrapods (Tetrapodomorpha) 25
2.1.4 Carboniferous tetrapods or tetrapodomorphs? 31
2.2 The amniote stem-group 32
2.2.1 Anthracosauria 33
2.2.2 Seymouriamorpha 37
2.2.3 Chroniosuchia 38
2.2.4 Lepospondyli 40
2.2.4.1 Lepospondyl characters 42
2.2.4.2 Microsauria 42
2.2.4.3 Lysorophia 44
2.2.4.4 Nectridea 44
2.2.4.5 Aïstopoda 45
2.2.4.6 Adelospondyli 46
2.2.4.7 Acherontiscidae 46
2.2.5 Gephyrostegida 46
2.2.6 Amniota 47
2.2.6.1 Stem-amniotes and early crown amniotes 48
2.3 The lissamphibian stem-group (Temnospondyli) 48
2.3.1 Edopoidea 51
2.3.2 Dendrerpeton and Balanerpeton 53
2.3.3 Dvinosauria 54
2.3.4 Dissorophoidea and Zatracheidae 54
2.3.5 Eryopoidea 56
2.3.6 Stereospondyli 57
2.4 Albanerpetontidae 58
2.5 Lissamphibia 59
2.5.1 Lissamphibian characters 61
2.5.2 Batrachia 62
2.5.2.1 Anura (frogs and toads) 62
2.5.2.2 Caudata (salamanders) 67
2.5.2.3 Gymnophiona (caecilians) 68
References 70
3 Amphibian Life Through Time 81
3.1 Aquatic predators prepare for land 83
3.2 Hot springs, scorpions, and little creepers 83
3.3 Life in the tropical coal forest 85
3.4 Neotenes explore unfavorable waters 89
3.5 Lowlands, uplands, and a cave 90
3.6 Hide and protect: extreme life in the hothouse 94
3.7 Predators in deltas, lakes, and brackish swamps 97
3.8 Stereospondyls in refugia, lissamphibians on the rise 97
3.9 Batrachians diversify, stereospondyls disappear 100
3.10 Lissamphibians expand into diverse habitats 101
References 102
4 The Amphibian Soft Body 106
4.1 How to infer soft tissues in extinct taxa 107
4.2 Fossil evidence: soft tissue preservation 109
4.3 Head and visceral skeleton 110
4.4 Respiratory organs 113
4.5 Lateral lines, electroreception, and ears 118
References 122
5 Evolution of Functional Systems 126
5.1 How paradigms and brackets give a functional scenario 127
5.2 Feeding and breathing under water 131
5.3 Decoupling breathing and feeding 134
5.4 Hearing: exapting the spiracle and hyomandibula 136
5.5 Respiration in early tetrapods 141
5.6 The evolution of terrestrial feeding 143
5.7 Transforming fins into limbs 144
5.8 Locomotion in paleozoic tetrapods 146
References 148
6 Development and Evolution 152
6.1 Ontogeny in modern amphibians 153
6.2 Fossil ontogenies 158
6.3 Ontogeny as a sequence: developmental trajectories 163
6.4 Histology: the skeleton as archive 167
6.5 Changing shape: allometry 171
vi
CONTENTS
6.6 Heterochrony: the evolution of development 174
6.7 Body plans: gene regulation and morphogenesis 179
References 184
7 Paleoecology 191
7.1 Lissamphibian ecology 192
7.2 Paleoecology: problems and perspectives 193
7.3 Paleozoic and Mesozoic amphibians 196
7.4 Amphibian evolution as a walk through trophic levels 203
References 205
8 Life History Evolution 208
8.1 Plasticity, reaction norm, and canalization 209
8.2 Reaction norms in extant amphibians 210
8.3 The biphasic life cycle in lissamphibians 211
8.4 Seymouriamorphs: biphasic life cycles without metamorphosis 213
8.5 Temnospondyls: flexible uni- and biphasic ontogenies 213
8.6 Lepospondyls: dwarfism and uniphasic life cycles 215
8.7 The evolution of metamorphosis 216
8.8 The evolution of neoteny 216
8.9 General features of life history evolution 217
References 219
9 Phylogeny 222
9.1 Phylogeny of amphibians 223
9.2 The big picture: tetrapod diversification 223
9.3 The origin of lissamphibians 224
References 231
10 Macroevolution 234
10.1 What is macroevolution? 235
10.2 Patterns of early tetrapod evolution 235
10.3 Major factors of amphibian evolution 240
10.4 Clades, space, and time 248
10.5 Diversity, disparity, and extinction 249
10.6 The evolution of terrestriality 252
References 254
Index 260
Plate section between pp. 124 and 125
vii
Contents
Preface
This book focuses on the first vertebrates to 1. How did fishes evolve the necessary structures
conquer the land, and on their long journey to and organs to survive on land?
become fully independent from the water. It will 2. What was the life of early tetrapods like?
trace the origin of tetrapod features and try to 3. Are modern amphibians a good model to
explain how and why they transformed into understand early tetrapods?
organs that permit life on land. The classic idea 4. How did modern amphibians acquire their
of early land vertebrates is that they were similar complex life cycles, encompassing an aquatic
to modern amphibians. Right or wrong, the vast larva, drastic metamorphosis, and a terrestrial
majority of early tetrapods are t herefore classified adult?
as amphibians (or more precisely their stem 5. How diverse were early land vertebrates, and
taxa). Accordingly, this book is centered on early which evolutionary strategies did they employ?
amphibian evolution, a topic that effectively 6. What were the major factors of amphibian
includes all early tetrapods, and it will also a nalyze evolution, and how did mass extinctions
facts and opinions on the origins of modern affect them?
amphibians. The major part of the story covers
events that occurred over the past 370 million We should not expect to find equally complete or
years, but it is far from restricted to paleontology. satisfactory answers to all of these questions, as
My own motivation to study the amphibian the problems remain at very different stages of
fossil record derives in large part from a fascina- research. Research questions that involve examin-
tion with the development, ecology, and evolution ing many fossilized hard parts may be relatively
of their modern representatives. Therefore I easy to solve, while others require inference from
consider many topics that can only be covered by extant taxa and will always remain more
examination of extant animals: features of the soft hypothetical. Yet other problems date back such a
body, functions of organs that mediate breathing, long time that the fossil record is too poor and
feeding, hearing, and locomotion, the morphogen- ambiguous to permit decisive answers – and in
esis of body parts, larval development, metamor- such cases we shall have to consider alternative
phosis, and ecology. solutions and discuss their plausibility.
The aim is to achieve a comprehensive picture of The diversity of questions relates also to the
amphibian evolution. This requires a walk through different research fields addressing them, and that
several dimensions, and I cannot claim to be an leads me to the second major focus of the
expert in all the fields to be covered. Nevertheless, book, which is to consider the various current
I hope that the outcome will be worth reading, even approaches and perspectives of paleobiology. The
though some data may become quickly outdated as study of amphibian morphology and paleontology
new finds are made, and some concepts may change exemplifies many aspects of evolution. This topic
with new insights. The following research questions offers a great opportunity to deepen our under-
illustrate the central problems of amphibian evolu- standing of how organisms survive under the most
tion as understood here: diverse range of c onditions, as both extant and