Embryos in Deep Time
The Rock Record of Biological Development
Publication Year: 2012
Can fossil embryos demonstrate evolutionary changes in reproductive modes? How have changes in ocean chemistry in the past affected the development of marine organisms? What can the microstructure of fossil bone and teeth reveal about maturation time, longevity and changes in growth phases? This book addresses these and other issues and documents with numerous examples and illustrations how fossils provide evidence not only of adult anatomy but also of the life history of individuals at different growth stages. The central topic of Biology today—the transformations occurring during the life of an organism and the mechanisms behind them—is addressed in an integrative manner for extinct animals.
Published by: University of California Press
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Title Page, Copyright
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I would like to thank the University of Zürich and its Faculty of Science, as well as the Institute of Paleontology, for providing an inspiring, challenging, and supportive environment in which I could write this book. ...
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The diversity of life is usually presented in evolutionary trees: A branching pattern culminates in figures of animals and plants. This is good, as trees convey the common history that organisms, including ourselves, share. But there is a limitation in this kind of representation. ...
1. Fossils, Ontogeny, and Phylogeny
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I remember as a child being very impressed by a statement, attributed erroneously to Thomas Huxley, that claimed that if monkeys were left alone in front of typewriters, they would type by chance and, given enough time, would indeed type the entire Encyclopaedia Britannica. I had an abridged version of the Encyclopaedia in Spanish, fifteen thick volumes, ...
2. Evo-Devo, Plasticity, and Modules
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The discipline that brings together the fields of developmental genetics and evolution has been baptized “evo-devo.” Few if any new aspects of evolutionary biology have received as much attention from practitioners and philosophers of biology. Evo-devo is purported to provide a new kind of synthesis of knowledge to understand the origin of biodiversity. ...
3. Fossilized Vertebrate Ontogenies
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Most fossil remains of vertebrates are mineralized portions of the skeleton. As the skeleton is at most only partially formed in embryos and in other juvenile stages, it is not surprising that most fossils are of adults or subadults, which are also larger than other life stages and thus more likely to be found. ...
4. Bones and Teeth under the Microscope
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As unlikely as it may seem, the most important piece of equipment for most paleontologists, besides the hammer, is the microscope. A large proportion of people studying extinct biodiversity work for the oil industry, examining the very small pollen of fossil plants or extinct foraminifera, the latter members of a group of single-celled organisms important for stratigraphic correlation between geologic sections. ...
5. Proportions, Growth, and Taxonomy
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At the time when little anatomical research of microscopic structures had been done, many people thought that eggs contained fully formed, very small individuals — or homunculi — a theory known as preformism (figure 23). Analogous “animalcules” were assumed for other species. ...
6. Growth and Diversification Patterns
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Fossils potentially provide direct evidence on how changes in growth strategies may have affected diversification patterns in geologic time. New strategies may have allowed some species to exploit new ecological opportunities or contributed to their demise. ...
7. Fossils and Developmental Genetics
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Ontogenies do not fossilize. But structures that do were once the result of a developmental process. Fossils of adult individuals can then be informative about development by virtue of preserving phenotypes with an immediate, clear correlation to a specific developmental process. ...
8. “Missing Links” and the Evolution of Development
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Many people are accustomed to thinking of the evolution of life in terms of a ladderlike progression, with a different animal on each rung. In the case of vertebrate evolution, they may envisage a fish on the bottom rung, a salamander on the next, then a lizard, a mouse, and finally a human on top. ...
9. Mammalian and Human Development
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There are about 5,300 species of extant mammals. They represent only a fraction of the number of species that ever existed since the separation of the evolutionary line leading to them, at least 315 million years ago. Then the reptilian and the mammalian lineages split. ...
10. On Trilobites, Shells, and Bugs
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So far I have mostly considered the evolution of vertebrate animals. There are many more living species of groups of animals other than vertebrates, and surely the same is true for extinct species. I aim in this chapter to present some of the discoveries in this area and the great potential the study of these animals has. ...
Epilogue: Is There a Moral to Developmental Paleontology?
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The history of life is a history of change, and much of that is recorded by fossils in deep time, in which a vast diversity of organisms originated and waned. Is there a moral message to be drawn from this? Of course not. There is no moral intrinsic to a scientific fact or hypothesis. ...
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Page Count: 265
Publication Year: 2012