Early animal evolution Precambrian *Ediacarian (Vendian) biota *First animals Cambrian explosion *First shelled animals *Evolution of animal diversity

Ediacarian (Vendian) Biota

First animal fossils Vendian animals Dickinsonia – annelid, cnidarian polyp, soft coral? Spriggina – annelid or arthropod? Nemiana – cnidarian medusa, or protist

Vendian = Edicaran Period Biota ~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?

The Cambrian Explosion Hard skeletal parts (shells of calcium carbonate & exoskeletons of chitin) Post Mya 54 out of 55 classes w/ skeletons today, appeared Burgess Shale

Cambrian Biota

Burgess Shale British Colombia rockies Shales are remains of deep water deposit of underwater mudslides ~ 515 Mya

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