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					| The Cambrian Explosion |  
					| Lecture 17 3/27/98
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					| |  | In the last two lectures, we looked at the fossil record from the late Precambrian and Cambrian times. | 
 |  | Today we will use that record to look at the Cambrian Explosion. | 
 |  | The Cambrian Explosion is a unprecedented time in the evolution of metazoans | 
 |  | Our understanding of the Cambrian Explosion is evolving | 
 |  | Small shelly fossils (ssf) | 
 |  | Development of nearly all of the modern metazoan phyla | 
 |  | slowly increasing O2 levels | 
 |  | end of Precambrian glaciation at 600 my | 
 | Causes for the Cambrian Explosion | 
 |  | Crossed a threshold value that allows hard part production | 
 |  | Easier to have evolutionary experiments | 
 |  | vertically burrowing organisms | 
 |  | development of teeth/predatory lifestyle | 
 
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