OUT OF THIN AIR



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Out of Thin Air: Dinosaurs, Birds, and Earth’s Ancient Atmosphere OUT OF THIN AIR

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Out of Thin Air: Dinosaurs, Birds, and Earth’s Ancient Atmosphere DINOSAURS, BIRDS, AND EARTH’S ANCIENT ATMOSPHERE OUT OF THIN AIR PETER D. WARD ILLLUSTRATIONS BY DAVID W. EHLERT, MAMS, CMI JOSEPH HENRY PRESS WASHINGTON, D.C.

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Out of Thin Air: Dinosaurs, Birds, and Earth’s Ancient Atmosphere Joseph Henry Press 500 Fifth Street, NW Washington, DC 20001 The Joseph Henry Press, an imprint of the National Academies Press, was created with the goal of making books on science, technology, and health more widely available to professionals and the public. Joseph Henry was one of the founders of the National Academy of Sciences and a leader in early American science. Any opinions, findings, conclusions, or recommendations expressed in this volume are those of the author and do not necessarily reflect the views of the National Academy of Sciences or its affiliated institutions. Library of Congress Cataloging-in-Publication Data Ward, Peter Douglas, 1949- Out of thin air : dinosaurs, birds, and Earth’s ancient atmosphere / Peter D. Ward. p. cm. Includes bibliographical references and index. ISBN 0-309-10061-5 (cloth) 1. Dinosaurs—Extinction. 2. Dinosaurs—Evolution. 3. Paleoecology. 4. Paleobotany—Carboniferous. I. Title. QE861.6.E95W37 2006 567.9—dc22 2006020396 Cover design by Van Nguyen. Cover images: Jerry L. Ferrara and Francois Gohier / Photo Researchers, Inc Copyright 2006 by Peter D. Ward. All rights reserved. Printed in the United States of America.

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Out of Thin Air: Dinosaurs, Birds, and Earth’s Ancient Atmosphere For Robert Berner, Navigator, who has so obviously relished the journey so far: You blazed a path to the old world

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Out of Thin Air: Dinosaurs, Birds, and Earth’s Ancient Atmosphere CONTENTS     Preface   ix     Acknowledgments   xiii     Introduction   1 1   Respiration and the Body Plans of Animal Life   9 2   Oxygen Through Time   31 3   Evolving Respiratory Systems as a Cause of the Cambrian Explosion   51 4   The Ordovician: Cambrian Explosion Part II   81 5   The Silurian-Devonian: How an Oxygen Spike Allowed the First Conquest of Land   89 6   The Carboniferous-Early Permian: High Oxygen, Fires, and Giants   111

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Out of Thin Air: Dinosaurs, Birds, and Earth’s Ancient Atmosphere           7   The Permian Extinction and the Evolution of Endothermy   133 8   The Triassic Explosion   159 9   The Jurassic: Dinosaur Hegemony in a Low-Oxygen World   199 10   The Cretaceous Extinction and the Rise of Large Mammals   223 11   Should We Fear the Oxygen Future?   229     References   237     Appendix   261     Index   265

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Out of Thin Air: Dinosaurs, Birds, and Earth’s Ancient Atmosphere PREFACE The highest peak of the great Himalayan mountains, Everest, tops out at 29,035 feet—nearly 6 miles above sea level. Its summit famously pokes into thin air, for at this height Earth’s atmosphere has already thinned to pressures more akin to Mars’s than to those found in the life-giving surface regions of Earth. Deadly, indeed, is that thin air—at least to those human climbers who dare enter it. But for other animals coming from the deep past, this is not the case. At Everest’s summit only a few humans can survive without oxygen augmentation and more often than not it was this factor that led to so many human deaths on this and other high mountains. There is sublime irony, then, in what may have been the last visions of some of those climbers as they lay dying. Surely some, staring upward into the pale blue regions where air pressure is even thinner than that which was killing them, watched the serene “V” of majestic geese flocks wending their way over the roof of the world, flying effortlessly thousands of feet above the Everest elevations that readily kill humans. Birds, it seems, care little for the physiological realities that rule us humans, us mammals, us creatures of ancestry far older than the birds themselves. Birds need far less oxygen than we ancient mammals. This book is, among other things, about why that is and how it came to be. That birds can not only exist at altitudes lethal to mammals but in this thin, oxygen-poor air also perform the most extreme athletic exer-

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Out of Thin Air: Dinosaurs, Birds, and Earth’s Ancient Atmosphere tion known in the animal kingdom—flying—is indeed a curiosity. But this is also a clue to a past that has only been recently discovered. The superiority of birds to any other group of vertebrates in terms of oxygen consumption has long been recognized. But it has been explained as a necessary adaptation to the athletic rigors of flying: birds need more oxygen because they exercise so hard and thus have evolved a more efficient lung system than ours. But this claim rings hollow, for the bird respiratory system found in the flyers is also found in non-flying birds. Something more fundamental seems to be at play. What if birds came from a time when even the surface of Earth, at sea level itself, had air as thin as that on Everest today? And if birds are so superior in thin air—what of their ancestors, the dinosaurs? We think of this world—our world—as being how it has always been, even knowing that conditions on Earth in the far past must have been as if from some distant and alien planet. Yet so it was. And on alien worlds we expect alien organisms. Should we then be surprised if organisms from a different kind of Earth, an earlier Earth with a low-oxygen atmosphere, were so alien as to surely qualify for some science fiction epic? Ordinarily we have considered dinosaurs, indeed most extinct animals, as creatures made up of some assemblage of familiar traits. For the dinosaurs, these believed assembled traits are mammalian and avian characteristics that form animals looking different from anything alive today but acting in familiar ways. But we now believe that this was surely not the case, that dinosaurs and many invertebrates now gone were much different from the living creatures of today. Rather, many dinosaurs, cold-blooded yet active, were adapted for life in low-oxygen conditions through a superb new kind of respiratory system and moved with cadence and rhythm as alien as creatures in the movies. They were animals not familiar at all. New discoveries in geology, geochemistry, and paleontology support this surprising claim and are the foundations of evidence that have led to the new history of life’s pageant on this planet, which is the subject and reason for this book. Long ago, it seems, when thin air was the norm, when animals gasped and died of altitude sickness even at sea level, when no animals clung to even low mountain tops, a new brand of creature evolved with a superb new lung system. Breathing

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Out of Thin Air: Dinosaurs, Birds, and Earth’s Ancient Atmosphere freely in the thin air, running down prey, or handily running away from lumbering predators that lacked this respiratory system, this stock of animals took over the world. We call them dinosaurs. Some of them, called birds, are famously still with us. This story also explains why the first common fossils in the Cambrian were segmented trilobites and why beautiful chambered cephalopods like our last holdout of that majestic race, the chambered nautilus, all but ruled the oceans for so long. And why creatures crawled from the seas, and why some then later crawled back in. All of these conclusions come from a new insight about the levels of that most necessary and most poisonous of gases, the giver and taker of life—oxygen.

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Out of Thin Air: Dinosaurs, Birds, and Earth’s Ancient Atmosphere ACKNOWLEDGMENTS It is not hard to know where to start in an otherwise usually difficult section to write: this book would not have been possible with out the interest, ideas, and especially the criticism of one of America’s greatest scientists, Dr. Robert Berner of Yale University. It is his seminal work that made this book possible, and if any good comes from the effort here, it is to Dr. Berner’s credit. The errors that undoubtedly have crept in are mine alone, however. I would like to thank the NASA Astrobiology Institute for funding the new science recounted in this book. I would like to thank the University of Washington and my colleagues in the Departments of Biology and Earth and Space Sciences for support during the writing of this book. Many people helped with the text and with ideas. I am especially indebted to Tom Daniel, Ray Huey, Billie Swalla, and most of all Roger Buick. Ms. Nomi Odano kept affairs together in such a way that allowed me to write this book. I would like to thank my agent, Sam Fleischman, for help along the way, and the excellent editorial and production staff at Joseph Henry Press, especially the heroic efforts of Ms. Lara Andersen. David Ehlert did a magnificent job with art. Special thanks to Ken Williford for research and guidance.

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