The First Mass Extinction of Complex lifeBy Marc Laflamme

Chemical and Physical Sciences, UTM

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The 540 Ma (million years ago) Cambrian Explosion represents the greatest expansion in early animal diversity on Earth. However, what is seldom realized is that this event was preceded by a diverse suite of large complex multicellular organisms: the Ediacara biota. These enigmatic organisms comprised both early animals and extinct lineages that disappeared from the fossil record altogether.

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Three hypotheses have been proposed to explain their disappearance:

1. An environmentally-driven Mass Extinction due to a rapid and global catastrophic environmental stress leading to the demise of the Ediacara biota,
2. The Cheshire Cat model that proposes a change in the geological and oceanographic conditions responsible for the fossilization of the Ediacara biota, making their preservation impossible. Thus their disappearance represents a failure of the fossil record rather than an extinction, and
3. a biologically mediated replacement that proposes a replacement of the Ediacara biota by animals due to the evolution of predation and complex food webs. In addition, the biotic replacement model predicts increasing evidence for ecosystem reorganization in response to the activity of newly evolved animals.

The disappearance of the Ediacara biota marks the demise of the first diverse array of large, complex multicellular organisms. Fieldwork combining geological and paleontological investigation from around the world (Newfoundland, Namibia, Australia, and Iran) has allowed me to evaluate the tempo and mode of the Ediacaran extinction, and give added context to the dramatic Cambrian radiation of complex animals. I was recently on Quirks and Quarks talking about this topic. It is particularly relevant given the attention that human-induced climate change is getting in the press these days. Here is a link to the interview, if you would like to hear it:

http://www.cbc.ca/radio/quirks/quirks-quarks-for-sep-19-2015-1.3233930/the-extinction-of-the-ediacarans-1.3233961