How Vertebrates Left the Water
Publication Year: 2010
Published by: University of California Press
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Title Page, Copyright, Dedication
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Life appeared in the oceans in a past so distant that it is diffi cult to imagine. The exact age of life on Earth is debated because the structures once considered to represent the oldest fossils (remains of ancient organisms, or traces which they left) have been reinterpreted as mineral crystallization in microscopic fractures by some paleontologists ...
ONE: HOW CAN WE RECONSTRUCT EVOLUTIONARY HISTORY?
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Our first ancestors were all aquatic. The oldest known vertebrates are about 500 Ma old, but the fi rst potentially terrestrial vertebrates are less than 350 Ma old. For more than 150 Ma, our ancestors swam with their fi ns and breathed through their gills; on dry land, these structures were very ineffi cient. Their sensory organs worked poorly in air, ...
TWO: CONQUEST OF LAND: DATA FROM EXTANT VERTEBRATES
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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 fi nned pre de ces sors. 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 ...
THREE: PALEONTOLOGICAL CONTEXT
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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
FOUR: VERTEBRATE LIMB EVOLUTION
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The limbs are the main locomotory structures in most tetrapods. There are of course exceptions (gymnophionans, snakes, etc.), but most tetrapods walk, run, or fl y 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 ...
FIVE: DIVERSITY OF PALEOZOIC STEGOCEPHALIANS
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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 ...
SIX: ADAPTATIONS TO LIFE ON LAND
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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 ...
SEVEN: SYNTHESIS AND CONCLUSION
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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 as Crassigyrinus, baphetids, and colosteids, which were not described in this book, ...
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Page Count: 216
Publication Year: 2010