Here's the description of the lecture posted on YouTube:
The Cambrian Explosion was one of the most important episodes in the history of life. Over some 20 to 25 million years, beginning about 543 million years ago, life in the oceans diversified. Today, we find abundant fossils of hard-shelled animals of this age in many parts of the world. The famous Burgess Shale of western Canada formed after the Cambrian Explosion but its unusually preserved fossils give paleontologists a glimpse of a nearly complete Cambrian community. These extraordinary fossils also show the wide range of animals that must have evolved earlier in the Cambrian Period. In this presentation, Westrop takes a look at recent research that gives us a new understanding of this evolutionary "explosion" of ocean life.