Gaining Ground, Second Edition

Jennifer A. Clack

Description

A Choice Outstanding Academic Title for 2013

Around 370 million years ago, a distant relative of a modern lungfish began a most extraordinary adventure—emerging from the water and laying claim to the land. Over the next 70 million years, this tentative beachhead had developed into a worldwide colonization by ever-increasing varieties of four-limbed creatures known as tetrapods, the ancestors of all vertebrate life on land. This new edition of Jennifer A. Clack's groundbreaking book tells the complex story of their emergence and evolution. Beginning with their closest relatives, the lobe-fin fishes such as lungfishes and coelacanths, Clack defines what a tetrapod is, describes their anatomy, and explains how they are related to other vertebrates. She looks at the Devonian environment in which they evolved, describes the known and newly discovered species, and explores the order and timing of anatomical changes that occurred during the fish-to-tetrapod transition.

Preface
Acknowledgments
One Introduction
Two Skulls and Skeletons in Transition
Three Relationships and Relatives: The Lobe-Fin Family
Four Setting the Scene: The Devonian World
Five The First Feet: Tetrapods of the Famennian
Six From Fins to Feet: Transformation and Transition
Seven Emerging into the Carboniferous: The First Phase
Eight East Kirkton and the Roots of the Modern Family Tree
Nine The Late Carboniferous: Expanding Horizons
Ten Gaining Ground: The Evolution of Terrestriality
References
Index

Sujets

• Sciences de la nature
• Biologie
• Life Sciences
• Fossils
• Sciences et techniques
• Biology
• Rock (geology)
• Paleontology
• Evolution
• 454 Life Sciences
• Rocks
• Science

Informations

• Publié par: Indiana University Press
• Date de parution: 27 juin 2012
• Nombre de lectures: 0
• EAN13: 9780253005373
• Langue: English
• Poids de l'ouvrage: 3 Mo

Extrait

GAINING GROUND
Life of the Past James O. Farlow, editor

This book is a publication of
Indiana University Press
601 North Morton Street Bloomington, Indiana 47404-3797 USA
iupress.indiana.edu
Telephone orders 800-842-6796 Fax orders 812-855-7931
2012 by Jennifer A. Clack
All rights reserved
No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and recording, or by any information storage and retrieval system, without permission in writing from the publisher. The Association of American University Presses Resolution on Permissions constitutes the only exception to this prohibition.
The paper used in this publication meets the minimum requirements of the American National Standard for Information Sciences-Permanence of Paper for Printed Library Materials, ANSI Z39.48-1992.
Manufactured in the United States of America
Library of Congress Cataloging-in-Publication Data
Clack, Jennifer A., 1937-
Gaining ground : the origin and evolution of tetrapods / Jennifer A. Clack. - 2nd ed.
p. cm. - (Life of the past)
Includes bibliographical references and index.
ISBN 978-0-253-35675-8 (cloth : alk. paper) - ISBN 978-0-253-00537-3 (e-pub) 1. Lungfishes, Fossil. 2. Amphibians, Fossil. 3. Leg-Evolution. 4. Paleontology--Devonian. 5. Paleontology-Carboniferous. I. Title.
QE852.D5C57 2011
566-dc23
2011030438
1 2 3 4 5 17 16 15 14 13 12
Contents
PREFACE TO THE SECOND EDITION
ACKNOWLEDGMENTS
LIST OF ABBREVIATIONS

1 Introduction: The Origin and Evolution of Tetrapods
2 Skulls and Skeletons in Transition
3 Relationships and Relatives: The Lobe-Fin Family
4 Setting the Scene: The Devonian World
5 The First Feet: Tetrapods of the Famennian
6 From Fins to Feet: Transformation and Transition
7 Emerging into the Carboniferous: The First Phase
8 East Kirkton and the Roots of the Modern Family Tree
9 The Late Carboniferous: Expanding Horizons
10 Gaining Ground: The Evolution of Terrestriality

REFERENCES
INDEX
Preface to the Second Edition
Since the first edition of Gaining Ground was completed, much has happened in the field of early tetrapod paleontology and in the wider world that has affected not only the ideas and conclusions presented in the first edition, but also what paleontologists are able to do with material, the techniques that they use, and how easily and quickly things can be done.
One of the most significant events worldwide has been the global spread of the Internet, which has not only allowed discoveries to be published more quickly, but has enabled rapid searches for material and references. The ease and speed of access to references by electronic means and Internet search have improved enormously, allowing information and citations to be readily found at the touch of a button. It s hard to remember that in the late 1990s and the first couple of years of the 21st century, when the first edition was written, online connections were often slow and limited. Today, the ease and availability of electronic techniques has greatly affected many aspects of producing and delivering a wide range of scientific output. I personally have been most affected by my familiarity with software packages such as Photoshop, which permits manipulation of scanned images to produce diagrams. Some of the diagrams in the first edition were admittedly clumsy, and I hope that readers will find these improved in the second. Digital photography, of course, is another boon.
Technological advances have affected many areas of study, and paleontology is no exception here. One of the techniques that has improved in availability, cost, and degree of resolution is that of X-ray computed tomography ( CT ), or micro- CT scanning. This is becoming the technique of choice for examining new aspects of fossil material previously inaccessible. Software programs build the serial sections produced by scans into three-dimensional images that can be easily manipulated and dissected. These have become more sophisticated but at the same time more amenable to being run on a moderately powerful desktop computer, as well as becoming more intuitive to use. Such advances have allowed new questions to be framed and answered. One stage up from micro- CT scanning with X-rays is the use of a synchrotron. This allows minute examination of tissue structure inside fossil material, from which, for example, three-dimensional images of growth patterns of bone can be built. For really high-resolution scanning to get these results, at present, the limitation of this technique is the small size of sample that can be examined at any one time. Larger specimens can be scanned at lower resolution, often higher than with micro- CT machines, but results still depend on the geological makeup of the material.
Micro- CT images of fossils are increasingly being used in biomechanical studies using an engineering technique known as finite element analysis ( FEA ). This allows study of the relative degrees and directions of stress that a structure, such as a skull, can withstand, thus permitting function to be inferred. Although FEA has not yet been widely applied to very early tetrapods, such analysis of lower jaw function, for example, should help reveal what the implications are for the changes in dental patterns seen across the fish-tetrapod transition. Such work is in progress.
Digital imaging and suitable computer programs allow quantitative studies of, for example, skull proportions, or the way in which different bones contribute to skull structure in different groups. This study, known as geometric morphometrics, is being applied to groups of fossil tetrapods. It can help tease apart differences in shapes among a range of taxa to reveal phylogenetic or morphological relationships, and some of the results are included in this new edition.
New electronic techniques have also been brought to bear on climate modeling and atmospheric composition in past periods of Earth s history, and these are highly relevant to understanding the late Paleozoic and events that occurred during that time.
Computers increased memory, faster processing power, and lower cost have allowed increasingly large data sets of taxa and characters to be used in phylogenetic analyses, and new search protocols and methods are beginning to provide alternative ways of processing the information. Some of these advances have been made in the field of molecular phylogenetics and in the incorporation of morphological and molecular data into combined analyses.
Cladistic matrices and the trees they generate are now being interrogated further in metadata analyses to produce hypotheses of overall evolutionary patterns: diversity and disparity curves, effects and results of evolutionary constraints or restrictions on taxa, episodes of character release (i.e., increasing the number of potentially varying characters) or decreased rates of character change, evolution of body size among clades, and many others (e.g., Ruta et al. 2006; Wagner et al. 2006; Laurin 2004).
The electronic age has seen a veritable explosion of information in the field of evolutionary developmental biology, or evo-devo. In its infancy in the early 1990s, it has more recently been asking questions in a phylogenetic context, incorporating ideas and data from phylogenies that have been drawn by means of both molecular and morphological data and that include fossil taxa. Paleontology has much to contribute to that endeavor, but similarly, researchers in evo-devo fields have been addressing questions on the basis of phylogenetically relevant species. Sharks, lungfish, and nonteleost fish are examples of these species, which have provided key information in studies such as the origin of limbs and digits.
Within the field of early tetrapod vertebrate paleontology, there have also been major developments of a more traditional kind. People have gone out and found more fossils. The number of recognizably different taxa of Devonian tetrapods has increased more or less exponentially since the mid-1990s, and discoveries are still going on. It is true that similarly explosive expansion has occurred in other fields of vertebrate paleontology as well, so my field appears to be part of a general trend. In fact, this probably applies to all aspects of scientific discovery, and a good part of the explanation is embodied in the electronic advances outlined above. But for the field covered in this book, there are particular areas in which major steps have been taken. The increasing information on elpistostegalian fish, like the discovery of Tiktaalik and micro- CT scanning of parts of Panderichthys and Ichthyostega , has added excitement, complexity, and some frustration to the field. The recent announcement of apparently tetrapod-like trackways in deposits 18 million years before tetrapod-like animals were supposed to exist is another surprise whose implications need to be assessed.
Two other fossil tetrapod groups have been the subjects of revived interest, generating new finds and new analyses. One of these is the temnospondyls, and in particular the group called dissorophoids. For some members of this group, we now have significant and useable growth series, and for others, we simply have far more relevant taxa. The lepospondyls are another group on which attention has been focused, from both morphological and phylogenetic points of view. This is one reason why readers will find much expanded sections on both of these groups and why the review of their relationships is much more complex and perhaps more confusing than it was. It reflects the efforts of key researchers in these various fields, which has been quite intense and difficult to summarize.
As I was writing the first edition, very little indeed was known about the environmental conditions in which early tetrapods lived. A review of the first edition commented on the lack of informatio