Early animal evolutionEarly animal evolution

• Precambrian

* Ediacarian (Vendian) biota

* First animals

• Cambrian explosion

* First shelled animals

* Evolution of animal diversity

Ediacarian (Vendian) BiotaEdiacarian (Vendian) Biota

First animal fossilsFirst animal fossils• Vendian animals

Dickinsonia – annelid, cnidarian polyp, soft coral?Spriggina – annelid or arthropod?

Nemiana – cnidarian medusa, or protist

Vendian = Edicaran PeriodVendian = Edicaran PeriodBiotaBiota

• ~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 The Cambrian Cambrian ExplosionExplosion

• 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

Cambrian BiotaCambrian Biota

Burgess ShaleBurgess Shale

• British Colombia rockies

• Shales are remains of deep water deposit of underwater mudslides

• ~ 515 Mya

Cambrian Explosion- Cambrian Explosion- reasonsreasons

• 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