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Download Early History Of Life and Animal Origins
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ZO 150 by Cable TV Presentation Notes Early History Of Life and Animal Origins "describing (rock) layers" Assumptions: Fossil Stratigraphy Fig. 26.4c • layers sequenced in time – rocks nearer the surface are younger • same fossils in different rocks means both rocks are the same age Many fossils can be aged by isotope ratios. Geological Time and Patterns • An Era includes several Periods • New Eras and Periods are defined by changes in types of fossils in rock strata • Mass extinctions were followed by adaptive radiations • Extinctions were caused by celestial or global, climatic events Clock Analogy for Geologic Time Fig. 26.2 Life Before Animals Fig. 26.1 Precambrian Table 25.1, Detail 1 Ediacara Fossils (about 600 Mybp) • Mybp = millions of years before present • late Precambrian rocks in Australia • oldest strata with animal-like fossils Ediacara Fossils and Modern Sea Pen 1 ZO 150 by Cable TV Presentation Notes Paleozoic Table 25.1, Detail 2 Cambrian Explosion • Genetic “clocks” indicate first animals evolved about 1,000 Mybp • Fossils show only very simple designs until Cambrian Period, 540 Mybp • ”Suddenly,” nearly every existing phylum and several extinct ones have diverse Cambrian fossils – Probably over fewer than 10 My First Appearances of Animal Fossils Fig. 26.8 Burgess Shale • Rock formation in Rocky Mountains of Alberta, Canada – deposited ~ 540 Mybp in marine environment • Fossils show fine details, because they were buried quickly by fine, anaerobic mud • Among oldest fossils readily classifiable to modern phyla of animals Burgess Shale Community Fig. 32.13 Early Cambrian Period Animals Modern Animal Taxa from the Burgess Shale Weird Wonders More, Early Cambrian Animals (unknown phyla) A Chordate (our phylum) from the Burgess Shale 2 ZO 150 by Cable TV Presentation Notes Patterns of Animal Evolution (class Web site) Animal Extinction Rates Fig. 25.5 Questions 1. Why do you think animals evolved later than other kingdoms? 2. Are more complex and larger animals continuing to evolve today? 3. Are the sponges we see now the ancestors of other animals, including us? 3
