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  • graptolites
    • composed of schleroprotein which is resistant to decay
    • planktonic - worldwide distribution
    • facies free
    • found in black shales - they'd die and sink to the bottom
    • good zone fossils
      • evolved rapidly and died quickly
      • abundant
      • absent from shallow water
    • basic evolutionary trends throughout ordovician
      • stipes change from many to few
      • thecae become more spread out and complex
      • stipes go from pendant (pointing down) to scandent (pointing up)
      • thecae change from pointing inwards to outwards
    • evolve: early Ordovician dominant: late Ordovician and early Silurian extinct: Devonian


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