1. Cambrian Explosion & Protostome Diversity
Darwin’s Dilemma

2. Timeline of Earth History

3. The Cryogenian
Periods of global glaciation ( MYA) Sponges appear in the fossil record (~760MYA)

4. Ediacaran
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

5. Ediacaran or Vendian faunas

6. 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 M above current level

7. Transition from Ediacaran to Cambrian faunas

8. Radiation and extinction

9. Animals with body cavities
By KDS 444
From bio.Rutgers.edu

10. Arthropod body plans

11. The Cambrian Explosion
Period of rapid diversification in form around ~ 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)

12. From Fox (2016). Nature 530:

13. From Lee et al. (2013)

14. 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

15. From: Smith, M. P. and D. A. T. Harper. 2013
From: Smith, M. P. and D. A. T. Harper Causes of the Cambrian explosion. Science. 341(6152):

16. Predator-Prey Arms Race

17. The Burgess Shale fauna (508 mya)

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