1. Cambrian Explosion Darwin’s Dilemma

2. The Cryogenian Periods of global glaciation (635-850 MYA) Sponges appear in the fossil record (~760MYA)

3. Ediacaran 635-542 MYA Begins at the cap carbonate that forms following a glaciation event (at the last one of the Cryogenian) Vendian or Ediacaran fauna strange quilted animals Some evidence of burrowing beneath the microbial mats

4. The Cambrian Period ~541-485 MYA Atmospheric oxygen ~12.5% (63% current level) Carbon dioxide concentration ~16X current level Temperature 7C above current level Sea level 30-90 M above current level

5. The Cambrian Explosion Period of rapid diversification in form around ~542-521 MYA. Almost all animal phyla appeared in the fossil record in a 20 million year window. Genomic and trace fossil evidence suggests that the bilaterian genetic toolkit appeared >100 million years earlier. Erwin et al. (2011)

6. From Lee et al. (2013)

7. Causes of the ‘Explosion’ Change from horizontal burrows just above to just below biofilms to burrows that mix sediment Increase in oxygen concentrations Allow larger body sizes. Hidden microscopic diversity becomes apparent Eyes and the appearance of predation Calcium becomes abundant Treptichnus pedum

8. Predator-Prey Arms Race

9. Changes in Evolutionary Faunas of Heavily-Armored Animals Modified from Sepkoski (1984)