Slide #1.

Cambrian Explosion Darwin’s Dilemma
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Slide #2.

The Cryogenian Periods of global glaciation (635-850 MYA) Sponges appear in the fossil record (~760MYA)
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Slide #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
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Slide #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
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Slide #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)
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Slide #6.

From Lee et al. (2013)
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Slide #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
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Slide #8.

Predator-Prey Arms Race
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Slide #9.

Changes in Evolutionary Faunas of HeavilyArmored Animals Modified from Sepkoski (1984)
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