Dawn of the Dinosaur Age begins, in Section One, by looking at the geological and climatic aftermath of the end-Permian extinction and the conditions of the early Mesozoic Era that created opportunities for archosaurian vertebrates, including dinosaurs. Chapter 1 describes the widespread changes to ocean and land environments, including worldwide changes to climates that served as catalysts for the spread of the archosaurs. Among these changes was another important set of mass-extinction events at the end of the Triassic
Period. Chapter 2 introduces the archosaurs of the Early Triassic that led to the rise of the dinosaurs and their relatives. In Chapter 3, the earliest dinosaurs are described, along with reasons for their rapid rise to a position of dominance over many other animals of the Mesozoic Era. Was their success due to good luck, or to better genes?
Section Two, Dinosaurs of the Early Mesozoic Era, introduces the major groups of dinosaurs. Chapter 4 presents the two major divisions of dinosaurs: the Saurischia, or "lizard-hipped" dinosaurs, and the Ornithischia, or i bird-hipped" dinosaurs. The chapter then goes on to look closely at the carnivorous saurischian dinosaurs: their traits, their lifestyles, and the earliest examples of their kind. Chapter 5 describes the early evolution of the other major clade of saurischians, the giant, long-necked herbivores. The chapter explores their early evolution, their traits, and the adaptations that led to their great success. Chapter 6 describes the origin and traits of the earliest members of the Ornithischia, the other major dinosaur clade, which consisted of diverse plant eaters.
Each chapter uses tables, maps, figures, and photos to depict the life, habitat, and changing evolutionary patterns that affected the lives of the early dinosaurs and their kin. Several chapters also include "Think About It" sidebars that elaborate on interesting issues, people, and discoveries related to Mesozoic life.
Dawn of the Dinosaur Age builds on foundational principles of geology, fossils, and the study of life. Readers who want to refresh their knowledge of certain basic terms and principles in the study of past l ife—or who seek to learn those principles for the first time—may wish to consult the glossary in the back of Dawn of the Dinosaur Age. Perhaps most important to keep in mind are the basic rules governing evolution: The direction of evolution is set in motion first by the genetically determined traits inherited by individuals, coupled with the interaction of that individual with its habitat. Changes accumulate, generation after generation, and allow species to adapt to changing conditions in the world around them. As Charles Darwin (1809-1882) explained, "The small differences distinguishing varieties of the same species steadily tend to increase, till they equal the greater differences between species of the same genus, or even of distinct genera." These are the rules of nature that drove the engine of evolution during the Paleozoic and gave rise to forms of life whose descendants still populate the Earth.
SECTION ONE: The World of the Dinosaurs k'i r
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