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Embryos in Deep Time

Embryos in Deep Time: The Rock Record of Biological Development

Marcelo Sánchez
Copyright Date: 2012
Edition: 1
Pages: 265
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  • Book Info
    Embryos in Deep Time
    Book Description:

    How can we bring together the study of genes, embryos and fossils?Embryos in Deep Timeis a critical synthesis of the study of individual development in fossils. It brings together an up-to-date review of concepts from comparative anatomy, ecology and developmental genetics, and examples of different kinds of animals from diverse geological epochs and geographic areas. 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.

    eISBN: 978-0-520-95230-0
    Subjects: Paleontology

Table of Contents

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  1. Front Matter
    (pp. i-iv)
  2. Table of Contents
    (pp. v-vi)
    (pp. vii-x)
    (pp. xi-xiv)

    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. The organisms portrayed are static entities, usually adults with the recognizable features of their species. In reality, organisms change throughout their lives. If we wanted to portray the biology of biodiversity, we could show for each organism a high-speed film of the different phases of its life history—for a multicellular organism, from fertilization to death....

  5. ONE Fossils, Ontogeny, and Phylogeny
    (pp. 1-33)

    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 entireEncyclopaedia Britannica.I had an abridged version of theEncyclopaediain Spanish, fifteen thick volumes, so I had an idea of the extent of text involved. I read the statement for the first time in a creationism booklet, which pointed out the absurdity of the statement.¹ But it made sense to me: unlikely, and yet, given infinite time,...

  6. TWO Evo-Devo, Plasticity, and Modules
    (pp. 34-45)

    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. For this reason, it is important to ponder how paleontology contributes to this area. The central focus of evo-devo is contested. Some see it as explaining the evolution of the capability to evolve, or evolvability. Many see it as explaining evolutionary novelties or innovations in the sense...

  7. THREE Fossilized Vertebrate Ontogenies
    (pp. 46-65)

    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. But fossils of embryos and of young individuals do exist. In a recent survey on reptiles, my colleague Massimo Delfino and I identified hundreds of scientific papers documenting such specimens (, most of them concerning dinosaurs. Some fossils are interpreted as hatchlings or neonates, but considering...

  8. FOUR Bones and Teeth under the Microscope
    (pp. 66-91)

    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. For paleontologists, the microscope enables also the study of the tissue microstructure of fossils, in particular the bone, which has become an important matter of investigation concerning development in extinct taxa.

    The study of living tissues, or histology, is...

  9. FIVE Proportions, Growth, and Taxonomy
    (pp. 92-104)

    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. This idea seems ridiculous to us now, but at the time there were no microscopes and evolutionary transformations among organisms were not understood. What is really remarkable, and makes much less sense without a modern acquaintance with biology, is how an egg cell and a spermatozoid can collectively represent the information and capacity to survive and develop into a whole...

  10. SIX Growth and Diversification Patterns
    (pp. 105-125)

    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. The evolutionary patterns of groups of organisms in geologic time, commonly referred to as clade dynamics, are the subject of intense research in the sector of the paleontological community working with invertebrate animals. Work in this area involves in many cases large databases and mathematical models based on several variables.

    Diversification rates, meaning how fast or slow the number of species in a group...

  11. SEVEN Fossils and Developmental Genetics
    (pp. 126-140)

    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. To reconstruct such a process, it is important to consider the position of the fossil in the evolutionary tree of life, to ensure that the analyses are based on correct assumptions. This approach is called extant phylogenetic bracketing. It was introduced specifically to infer soft anatomical properties and behavioral reconstructions in fossils, but it can also be used for...

  12. EIGHT “Missing Links” and the Evolution of Development
    (pp. 141-157)

    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. Following this medieval myth, it seemed natural to suppose that “lower” animals evolved into “higher” animals. And if this were so, we should expect to see “links” between them, all the way up and down the “ladder.” This idea of the Great Chain of Being,...

  13. NINE Mammalian and Human Development
    (pp. 158-175)

    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. The estimate based on fossils is that about 100 million years passed until the appearance of the last common ancestor of all living mammals in the Jurassic.¹ Although 5,300 extant species sounds like a large number, it is not so impressive when compared with other groups: there are twice as many species of birds and...

  14. TEN On Trilobites, Shells, and Bugs
    (pp. 176-194)

    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. To do justice to developmental paleontology in invertebrates, a full treatment of the subject would be necessary, and that is certainly not attempted here.

    The vertebrate skeleton, which is what is most commonly preserved as a fossil, is found inside the body and...

  15. EPILOGUE: Is There a Moral to Developmental Paleontology?
    (pp. 195-196)

    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. Not so long ago our understanding of evolution, including that of humans, was dominated by the idea of the selfish gene. More recently biological anthropologists have demonstrated that we humans are cooperative great apes and that this is biologically ingrained. This new knowledge of biology does...

  16. NOTES
    (pp. 197-212)
    (pp. 213-242)
  18. INDEX
    (pp. 243-256)
  19. Back Matter
    (pp. 257-257)