Early%20animal%20evolution

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Early animal evolution

• Precambrian
• Ediacarian (Vendian) biota
• First animals
• Cambrian explosion
• First shelled animals
• Evolution of animal diversity

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Ediacarian (Vendian) Biota
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First animal fossils

• Vendian animals

Nemiana cnidarian medusa, or protist
Dickinsonia annelid, cnidarian polyp, soft
coral?
Spriggina annelid or arthropod?
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Vendian Edicaran PeriodBiota

• 610 to 540 Mya
• SE Australia, Northern Europe, elsewhere
• Shell-less
• Modern groups (cnidarians, sponges, annelids?)
• Some organisms in completely different phyla
• Vendian/Cambrian extinction due to glaciation?

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The Cambrian Explosion

• Hard skeletal parts (shells of calcium carbonate
  exoskeletons of chitin)
• Post 570-510 Mya
• 54 out of 55 classes w/ skeletons today, appeared
• Burgess Shale

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Cambrian Biota
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Burgess Shale

• British Colombia rockies
• Shales are remains of deep water deposit of
  underwater mudslides
• 515 Mya

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Cambrian Explosion- reasons

• Edicaran biota go extinct ? empty habitats?
• Higher oxygen levels?
• Changes in seawater chemistry?
• Continental configuration ? climate changes,
  ocean circulation
• Glaciation or deglaciation ? sea level change
• Extra-terrestrial cause