Turtles as Hopeful Monsters

Olivier Rieppel

Description

Where do turtles hail from? Why and how did they acquire shells? These questions have spurred heated debate and intense research for more than two hundred years. Brilliantly weaving evidence from the latest paleontological discoveries with an accessible, incisive look at different theories of biological evolution and their proponents, Turtles as Hopeful Monsters tells the fascinating evolutionary story of the shelled reptiles. Paleontologist Olivier Rieppel traces the evolution of turtles from over 220 million years ago, examining closely the relationship of turtles to other reptiles and charting the development of the shell. Turtle issues fuel a debate between proponents of gradual evolutionary change and authors favoring change through bursts and leaps of macromutation. The first book-length popular history of its type, this indispensable resource is an engaging read for all those fascinated by this ubiquitous and uniquely shaped reptile.

Acknowledgements
Introduction
1. Misplaced Turtles
2. Reptile Classification and Evolution
3. Levels of Evolution
4. Hopeful Monsters
5. The Turtle Shell
6. Fossil Hunting in China
Bibliography
Index

Sujets

• Sciences de la nature
• Biologie
• Sciences et techniques
• Turtles
• Paleontology
• Evolution
• Turtle
• Science

Informations

• Publié par: Indiana University Press
• Date de parution: 13 mars 2017
• Nombre de lectures: 0
• EAN13: 9780253025074
• Langue: English
• Poids de l'ouvrage: 2 Mo

Extrait

Turtles as Hopeful Monsters
Life of the Past
James O. Farlow, editor
Indiana University Press
Bloomington and Indianapolis
TURTLES AS HOPEFUL MONSTERS
Origins and Evolution
OLIVIER RIEPPEL
This book is a publication of
Indiana University Press
Office of Scholarly Publishing Herman B Wells Library 350 1320 East 10th Street Bloomington, Indiana 47405 USA
iupress.indiana.edu
2017 by Olivier Rieppel
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 China
Library of Congress Cataloging-in-Publication Data
Names: Rieppel, Olivier.
Title: Turtles as hopeful monsters / Olivier Rieppel.
Description: Bloomington : Indiana University Press, [2017] | Series: Life of the past | Includes bibliographical references and index.
Identifiers: LCCN 2016031981 (print) | LCCN 2016050733 (ebook) | ISBN 9780253024756 (cl) | ISBN 9780253025074 (eb)
Subjects: LCSH: Turtles. | Turtles- Evolution. | Reptiles-Evolution. | Evolutionary paleobiology.
Classification: LCC QL666.C5 R57 2017 (print) | LCC QL666.C5 (ebook) | DDC 597.92-dc23
LC record available at https://lccn.loc.gov/2016031981
1 2 3 4 5 22 21 20 19 18 17
Contents
C

ACKNOWLEDGMENTS

Introduction: Turtles as Hopeful Monsters
1
Misplaced Turtles
2
Reptile Classification and Evolution
3
Levels of Evolution
4
Hopeful Monsters
5
The Turtle Shell
6
Fossil Hunting in China

LITERATURE CITED

INDEX
Acknowledgments
A
I AM VERY GRATEFUL TO LI CHUN, INSTITUTE OF VERTEBRATE PALE ontology and Paleoanthropology, Beijing, who invited me to collaborate in the description of many fine fossils he collected. I am equally thankful to Janice Frisch, acquisition editor at the Indiana University Press, and series editor James O. Farlow for their interest in the project, as well as their help and support to see this book through to publication. Marlene Donnelly (scientific illustrator) and John Weinstein (photographer) from the Field Museum of Natural History, Chicago, offered their help and expertise in the illustration of the book. Christine Giannoni offered equally invaluable help in obtaining often obscure literature.
The Henry Fairfield Osborn Papers, curated in Archives of the American Museum of Natural History, were kindly made available by my son, Lukas Rieppel. I also thank the staff at the German Federal Archives (formerly Berlin Documentation Center) and the University Archives of G ttingen and Greifswald for their help and support in my research.
Last but not least, I thank my wife, Myriam, and our sons, Michael and Lukas, who accompanied me on a journey that allowed me to pursue the research recounted in this book.
Turtles as Hopeful Monsters
Introduction: Turtles as Hopeful Monsters
I
HERE THEY ARE, STILL WITH US, BOXED UP IN A SHELL, SEEMING survivors of the distant geologic past: prehistoric creatures that both predated and outlived the dinosaurs. As a symbol in Hindu and Chinese mythology, the turtle supports the earth-but what supports the turtle? The philosophically intriguing answer is this: it s turtles all the way down. Sluggish on land, seemingly stubborn in their behavior, turtles came to symbolize longevity, strength, and endurance in ancient China. The longevity of the turtle lineage is indeed remarkable, as is its evolutionary strength if measured by the numbers of species that have populated Earth for at least 220 million years, which is the approximate age of the oldest fossil turtle currently known. (For a discussion of fossils some 260 million years old, controversially interpreted as the oldest stem-turtle, see chap. 3 .) In spite of their highly constrained body plan, turtles show a surprising potential for evolutionary diversification, with species that conquered a great variety of habitats: forests and grasslands, deserts and karst mountains, rivers, ponds, lakes, even the open sea, with some 331 living species currently recognized (Fritz and Havas, 2007; van Dijk et al., 2012).
As Adler has remarked, Turtles are one of nature s most immediately recognizable life forms (2007:139), bizarre in their own way, which is what seems to attract people s attention as well as scientists curiosity. Where do turtles come from, and how did their unique anatomy and bodily functions evolve? These are questions that have spurred intense research as well as heated debate for 200 years and more. Yet even in the wake of the development of revolutionizing techniques in modern molecular biology, the answer remains as elusive as ever. Progress has been made, but a lot still remains to be discovered.
The eminent twentieth-century evolutionary biologist Theodosius Dobzhansky once noted, Nothing makes sense in biology except in the light of evolution (1973:125). Philosophers of biology Kim Sterelny and Paul E. Griffiths paraphrased this famous line as, Nothing in biology makes sense except in the context of its place in phylogeny, its context in the great tree of life (1999:379). To ask where turtles come from is to raise the question of turtle ancestry. It certainly is uncontroversial that turtles are reptiles, but that does not tell us what group of reptiles gave rise to the turtle lineage in the distant part. What was the ancestor of turtles? That question was certainly a legitimate one to ask in the middle of the twentieth century and earlier, when the study of fossils was largely motivated by the search for ancestors of still-living descendants. The study of fossils retrieved from successive layers of rock was at that time compared to leafing through an illustrated book on evolution, supposedly revealing a gallery of ancestors and descendants.
Paleontologists started to research the ancestry of turtles well back in the nineteenth century, but until recently, all the fossil turtles pulled from sedimentary rock spanning vast geologic time were already finished exemplars, complete with carapace and plastron. It s indeed turtles all the way down! In the 1970s and 1980s, however, the study of evolutionary relationships was revolutionized; comparative biology went through a cladistic revolution. The search for ancestors was rejected as dilettante science; instead, the search for sister groups became all the rage. When, through evolutionary time, a species lineage splits into two, the stem species gives rise to two daughter species. These two daughter species are sister species; their respective descendants thus form sister groups. Rather than asking what was the ancestor of turtles, the question-in the aftermath of the cladistic revolution-must be, what kind of a reptile species was it that shared with the turtle lineage a common ancestor that was not also ancestral to any other reptile lineage? In other words, which lineage of reptiles is more closely related to turtles than either is to any other reptile group? To answer this question requires some foundational knowledge about the basic structure of the reptile skull and the various modifications it underwent as reptiles diversified into turtles, crocodiles, lizards, and snakes. This is because the skull, as well as other parts of the skeleton, may hold the key to understanding turtle origins. More recently, molecular data, in particular DNA data, have in large measure been adduced in the search for turtle origins. But in spite of all these efforts, the deep evolutionary history of the turtle lineage remains only dimly lit.
Some paleontologists may still maintain that turtles are living fossils, descendants of ancient stem-reptiles that have long vanished from the surface of the earth. Other authors, working mostly with skeletal features, have argued that turtles are more closely related to the tuatara and the scaly reptiles, such as lizards and snakes, than they are related to any other reptile group, including crocodiles and birds. Researchers working with DNA data, in contrast, have found that turtles are more closely related to crocodiles and birds than they are related to any other reptile group, including the tuatara and the scaly reptiles. Although discussion and debate continue, the current situation looks like one where the experts have agreed to disagree. Beyond hard yet still inconclusive evidence, rhetoric is also at work in science. Science is not just about observation and measurement; it is also about how scientists talk about their observations and measurements. The controversial case of turtle relationships provides prime examples of how the language used by a group of scientists can guide scientific inquiry in a particular direction to the exclusion of alternative perspectives. Science, at least the kind that seeks to decipher evolutionary relationships, does not happen in the germ-free environment of a clean lab, pursued by a cold, detached, and unbiased intellect. It is instead an eminently social enterprise, collaborative and competitive at the same time.
Better knowledge of turtle sister group relationships would certainly help to understand how the extravagant turtle body plan evolved. How did the turtle shell, its associated structures, and the consequent physiological peculiarities of turtles evolve? Everybody would certainly agree that a finished turtle, complete with carapace and plastron, differs radically in its anatomy from all other reptiles, such as crocodiles or lizards. But how are such radical evolutionary transformations possible? Darwin argued that evolution is a slow, gradual, stepw