Cowen's History of Life

Michael J. Benton, Michael J. Benton

• Publisher: Wiley-Blackwell
• Year: 2019
• ISBN:
  9781119482222
• Edition: 6
• Topic: Scienze biologiche
• Subtopic: Biologia

A newly revised and fully updated edition of the market-leading introduction to paleontology

Designed for students and anyone else with an interest in the history of life on our planet, the new edition of this classic text describes the biological evolution of Earth's organisms, and reconstructs their adaptations and the ecology and environments in which they functioned.

Cowen's History of Life, 6th Edition includes major updates, including substantial rewrites to chapters on the origins of eukaryotes, the Cambrian explosion, the terrestrialization of plants and animals, the Triassic recovery of life, the origin of birds, the end-Cretaceous mass extinction, and human evolution. It also features new chapters on plants, soils and transformation of the land; the Mesozoic marine revolution; and the evolution of oceans and climates. Beginning with the origin of the Earth and the earliest life on earth, the book goes on to offer insightful contributions covering: the evolution of Metazoans; the early vertebrates; life of vertebrates on land; and early amniotes and thermoregulation. The book also looks at: dinosaur diversity, as well as their demise; early mammals; the rise of modern mammals; the Neogene Savannas; primates; life in the ice ages; and more.

• Covers the breadth of the subject in a concise yet specific way for undergrads with no academic background in the topic
• Reorganizes all chapters to reflect the geological series of events, enabling a new focus on big events
• Updated with three brand new chapters and numerous revised ones
• Put together by a new editorial team internationally recognized as the global leaders in paleontology
• Filled with illustrations and photographs throughout
• Includes diagrams to show internal structures of organisms, cladograms, time scales and events, and paleogeographic maps
• Supplemented with a dedicated website that explores additional enriching information and discussion, and which features images for use in visual presentations

Cowen's History of Life, 6th Edition is an ideal book for undergraduate students taking courses in introductory paleontology, as well those on global change and earth systems.

1
The Origin of Life on Earth

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In This Chapter

First, we describe what geology and paleontology aim to study. But in dealing with the history of life, we have to face the most difficult question first: where did Earth’s life come from? Astronomers find that organic compounds exist almost everywhere in space, yet we only know of life on one planet: Earth. We discuss the planets and moons of our solar system, and there are good reasons why none of them (except Earth) have life. Life exists in cells, so we discuss at length how complex organic molecules might have come together inside cells which survived, reproduced, and evolved on the early Earth. Laboratory experiments have already mimicked many of the steps in that process in the laboratory, but there is still a lot of work to be done.

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How Geology Works

Geology is the study of the Earth we live on. It’s about fundamental ideas, such as origins and deep time, but also has immediate, practical aspects, such as guiding the commercial search for oil and useful minerals, as well as being core to understanding current and future climate change. Geology has methods and principles of its own, but also draws from many other sciences: physics, chemistry, biology, mathematics, and statistics are just a few. Geologists cannot be narrow specialists, because geology is a broad science that works best for people who think broadly. So, geologists cannot be successful if they are geeks (although a few seem to manage it). Above all, geology deals with the reality of the Earth: its rocks, minerals, its rivers, lakes, and oceans, its surface and its deep structure.

Some geologists deal with the Earth as it is now: they do not need to look at the past. Deep Earth history does not matter much to a geologist trying to deal with ecological repair to an abandoned gold mine. But many geologists do study Earth history, and they find that our planet has changed, at all scales of space and time, and sometimes in the most surprising ways. For 200 years, fossils have provided direct and solid proof of change through time. Life began and evolved on a planet that is changing too. Fossils often provide insight into Earth’s environmental changes, whether or not they survived those changes. Paleontology is not just a fascinating side branch of geology, but a vital component of it.

As they run their life processes, organisms take in, alter, and release chemicals. Given enough organisms and enough time, biological processes can change the chemical and physical world. Photosynthesis, which provides the oxygen in our atmosphere, is only one of these processes. In turn, physical processes of the Earth such as continental movement, volcanism, and climate change affect organisms, influencing their evolution, and, in turn, affecting the way they can make changes to the physical Earth. This gigantic interaction, or feedback mechanism, has been going on since life evolved on Earth. Paleontologists and geologists who ignore this interaction are likely to get the wrong answers as they try to reconstruct the past.

How Paleontology Works

Traces of Earth’s ancient life have been preserved in rocks as fossils. Paleontology is the science of studying these fossils. Paleontology aims to understand fossils as once‐living organisms, living, breeding, and dying in a real environment on a real but past Earth that we can no longer touch, smell, or see directly.

Most paleontologists do not study fossils for their intrinsic interest, although some of us do. Their greater value lies in what they tell us about ourselves and our background. We care about our future, which is a continuation of our past. One good reason for trying to understand ancient life is to manage better the biology of our planet today, so we need to use some kind of reasonable logic for clear interpretation of the life of the past.

Some basic problems of paleontology are much like those of archaeology and history: how do we know we have found the right explanation for some past event? How do we know we are not just making up a story?

Anything we suggest about the biology of ancient organisms should make sense in terms of what we know about the biology of living organisms, unless there is very good evidence to the contrary. This rule applies throughout biology, from cell biochemistry to genetics, physiology, ecology, behavior, and evolution.

There are three levels of paleontological interpretation. First, there are inevitable conclusions for which there are no possible alternatives. For example, there’s no doubt that extinct ichthyosaurs were swimming marine reptiles; look at their body shape (Figure 1.1) and compare it with a dolphin or a shark, and there is also the fact their skeletons are always found in marine sediments.

Figure 1.1 Guesses about ichthyosaur color patterns. (a) Ichthyosaur painting by Heinrich Harder 1916. (b) Art by Nobu Tamura, with muted colors (Wikimedia). (c) Stylistic artwork.

Source: © Danny Anduza, used by permission. See more of Danny's work at www.cafepress.com/dannysdinosaurs.

At the next level, there are likely interpretations. There may be alternatives, but a large body of evidence supports one leading idea. For example, there is good evidence that suggests ichthyosaurs gave birth to live young rather than laying eggs. The evidence includes dozens of fossils of mother ichthyosaurs carrying well‐developed babies inside their rib cages. Almost all paleontologists view this as the best hypothesis and would be surprised if contrary evidence turned up.

Then there are speculations. They may be right, but there is not much real evidence one way or another. Paleontologists, and indeed all other scientists, can accept speculations as tentative ideas to work with and to test carefully, but they should not be surprised or upset to find them wrong. For example, it seems reasonable that ichthyosaurs were warm‐blooded, but it’s a speculative idea because it’s difficult to test. If new evidence showed that the idea was unlikely, people might be disappointed but they would not be distressed scientifically.

It’s important for students of paleontology not to fall into the apologetic trap of saying, “Well, it all happened millions of years ago, so we can only really guess about stuff.” Not true! The geologic time scale is well established based on multiple dating evidence, and we know the past geography of the Earth as the continents moved, again based on multiple lines of evidence that agree.

This is the first point: we can often get at information about the past through multiple routes, and so we confirm our hypotheses with different, independent datasets. We have powerful tools to reconstruct exact patterns of evolution, as you will read in this and later chapters, and we know about times of crisis – mass extinctions – again through massive amounts of data and multiple lines of evidence. These basics cannot be denied, only modified as knowledge becomes more precise.

The other kind of analysis in paleontology is where we can test ideas numerically. For example, paleobiologists can calculate dinosaur running speeds using ancient trackways – you just need the stride length and the leg length and it’s...