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PPT05 - The Cambrian Explosion

PPT05 - The Cambrian Explosion - The Cambrian Explosion The...

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The Cambrian Explosion - The Rise of the Metazoans • Early Paleozoic: story of life in the oceans • No Freshwater fossils • PRESUMED microbial / fungal invasion of the land • Initial radiation of metazoan Life: Late Proterozoic Ediacaran Fauna (Australia, Russia) / Guizhou (China) Fauna Cambrian : Radiation of organisms with hard parts • Why at this time – Why not earlier? • 1. Calcium carbonate theory • Precambrian oceans deficient in calcium carbonate? • Nahhh! Loads of Precambrian carbonate rocks Majority of shells made of Calcium carbonate • 2. Metabolic Theory • Skeletons evolve as a response to removing mineral matter • ADVANTAGES: • - protection from UV -> shallower waters • - prevents desiccation -> intertidal environment • - supports soft tissue / aids locomotion • - predation protection Need to remove waste in Precambrian - Cambrian boundary recognized on the basis of emergence of metazoans: Trichophycus pedum : a trace fossil • More complex behavior / anatomy • Base of Phanerozoic: Fortune Head ref section, NF.
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