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How Vertebrates Left the Water

How Vertebrates Left the Water

Michel Laurin
Copyright Date: 2010
Edition: 1
Pages: 216
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  • Book Info
    How Vertebrates Left the Water
    Book Description:

    More than three hundred million years ago—a relatively recent date in the two billion years since life first appeared—vertebrate animals first ventured onto land. This usefully illustrated book describes how some finned vertebrates acquired limbs, giving rise to more than 25,000 extant tetrapod species. Michel Laurin uses paleontological, geological, physiological, and comparative anatomical data to describe this monumental event. He summarizes key concepts of modern paleontological research, including biological nomenclature, paleontological and molecular dating, and the methods used to infer phylogeny and character evolution. Along with a discussion of the evolutionary pressures that may have led vertebrates onto dry land, the book also shows how extant vertebrates yield clues about the conquest of land and how scientists uncover evolutionary history.

    eISBN: 978-0-520-94798-6
    Subjects: Paleontology

Table of Contents

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  1. Front Matter
    (pp. i-vi)
  2. Table of Contents
    (pp. vii-x)
    (pp. xi-xvi)
  4. CHAPTER ONE How Can We Reconstruct Evolutionary History?
    (pp. 1-44)

    Our first ancestors were all aquatic. The oldest known vertebrates are about 500 Ma old, but the first potentially terrestrial vertebrates are less than 350 Ma old. For more than 150 Ma, our ancestors swam with their fins and breathed through their gills; on dry land, these structures were very inefficient. Their sensory organs worked poorly in air, if at all, and had to undergo various modifications to adapt to life on the continents. The eyes of our ancestors lacked eyelids and tear glands and could dry out rapidly; their ears did not enable them to hear most airborne sounds,...

  5. CHAPTER TWO Conquest of Land: Data from Extant Vertebrates
    (pp. 45-54)

    The most direct source of information about the conquest of land by vertebrates is of course the Paleozoic fossil record of limbed vertebrates and their closest finned predecessors. However, the extant fauna also yields more indirect clues that are equally informative. Indeed, while fossils tell us about the morphology of extinct species, they often reveal little about the lifestyle of early vertebrates or the function of fossilized structures. To interpret fossils correctly, we must carefully study extant taxa, whose behavior and function can be observed. The extant taxa most relevant to studies about the conquest of land by vertebrates are...

  6. CHAPTER THREE Paleontological Context
    (pp. 55-72)

    To better understand the conquest of land by vertebrates, we must keep in mind a minimal amount of background information about the development of terrestrial ecosystems. Indeed, without the presence of green plants on continents, animals would have probably not colonized this new habitat, which was so different from the marine environment in which life was born. This chapter presents a brief survey of the appearance and evolution of various taxa in continental habitats.

    Plants ventured onto continents well before vertebrates, and probably before animals. Since plants form the basis of the food chain of most ecosystems, animal life on...

  7. CHAPTER FOUR Vertebrate Limb Evolution
    (pp. 73-98)

    The limbs are the main locomotory structures in most tetrapods. There are of course exceptions (gymnophionans, snakes, etc.), but most tetrapods walk, run, or fly using their limbs, which probably played an important role when our ancestors ventured onto land. To understand the colonization of land by vertebrates, we must study the origin and evolution of limbs, and especially of their skeleton, which is often the only part to fossilize.

    The vertebrate skeleton can be divided into an internal endoskeleton and a dermal skeleton, which is located in a more superficial position (in the deep part of the dermis and...

  8. CHAPTER FIVE Diversity of Paleozoic Stegocephalians
    (pp. 99-134)

    Among vertebrates, only stegocephalians have an autopod. Thus, stegocephalians include all terrestrial and most amphibious vertebrates. The main invasion of land by vertebrates occurred in the Carboniferous. To understand this event, a survey of the biodiversity and phylogeny of early stegocephalians is useful.

    Temnospondyls form a large group in which more than 150 genera are recognized. They appeared in the Early Carboniferous (about 340 Ma ago) and vanished in the Cretaceous, about 100 Ma ago. They include, among others,EryopsandMastodonsaurus.Temnospondyls were midsized to large, generally between 30 cm and 3 m in total body length, but at...

  9. CHAPTER SIX Adaptations to Life on Land
    (pp. 135-160)

    When vertebrates ventured onto land, most of their systems (locomotor, respiratory, sensory) and structures (like the skin and axial skeleton) were not optimal for terrestrial life. Life in this new environment must have been fairly diffi cult for these animals, and the selective pressures leading to adaptation to life on land must have been fairly strong. Adaptation as a process is evolution influenced by selective pressures; the same word also designates the end result of this evolution, namely, a character that improves fitness. Thus, the loss of internal gills early in stegocephalians history can be seen as a terrestrial adaptation....

  10. CHAPTER SEVEN Synthesis and Conclusion
    (pp. 161-168)

    The data summarized here can be used to present a preliminary reconstruction of the history of the conquest of land by vertebrates (Fig. 7.1).

    This synthesis suggests that all known Devonian stegocephalians were primitively aquatic. Some Carboniferous taxa, such asCrassigyrinus, baphetids, and colosteids, which were not described in this book, were probably also primitively aquatic, even though they probably had better terrestrial locomotion capabilities than those of Devonian stegocephalians. It is also possible that embolomeres were primitively aquatic, but this is uncertain because their last common ancestor with temnospondyls may have been amphibious. Some of the small-body and longer-legged...

    (pp. 169-174)
    (pp. 175-186)
  13. INDEX
    (pp. 187-199)
  14. Back Matter
    (pp. 200-200)