[MUSIC] The Burgess Shale format is an example another experiment that was run during the course of evolutionary biology. Where nature selected for and provided the constraints, and the environmental setting, and the ecological foundations for the evolution of a new type of organism. The Burgess Shale is named after an outcrop of rock that occurs in the Rocky Mountains of Canada. And the Burgess Shale itself was deposited in marine environments, shallow ocean deposits. They're very fine grained, so it would've been a muddy, relatively moderately shallow water depth. And these were organisms that lived on the sea floor and did very well in this Cambrian time period. Now, we have an example of another evolutionary experiment that took place in the, with the Evanachan farm. And that also did extremely well on a global scale and then went completely extinct soon after it originated. This is another example then, and so the Burgess Shale fauna has provided us with an amazing assortment of organisms. We see, first of all, crabs that look like some kind of an alien type of life form. These crabs have these large, spine-like projections that came around from the head and then it protected a whole series of segments that made up the body going back into the tail. So it had all these multiple parts that were moving forward, some of these were swimmers and some of these were benthic dwellers that lived on the sea floor and were able to crawl and move forward. As one example, we had crabs that were part of this assemblage, and because they are so intricate, we call them a lace crab. Another completely bizarre organism again we have nothing like this right now, we call Hallucigenia. And Hallucigenia looked like a, maybe a centipede with extremely long legs that had gigantic spikes coming off if it. And it's appropriately named because you try to describe this to someone and they'd assume that you were hallucinating. Again, we have nothing like this on the modern day sea floor, with all these multiple appendages and legs that allowed them to move forward. And then this very elaborate system for, we assume protecting them from predation. We also had a group of maybe less dramatic organisms but one's, organisms that lived both on the sea floor and up in the water. And they again made lifestyle success in ways that we've seen previously with some of the other organisms that came up in the Cambrian. But these Burgess Shale are explicitly different from any of the other ones we saw before. Another one of the ideas of the Burgess Shale is that we have a group of predators, that extremely well. And again that probably, because the predators were so successful, again help lead to the demise of these organisms. And one of the major types of predators, again it's just absolutely bizarre, we call it Opabinia. And Opabinia looked like some kind of a combination of, If you will. Some kind of maybe floating crab but then it had a very insect like head and then coming out from the front of the head it had one long projected appendage that had a big claw on the front. And that claw would move the prey that it attacked and devoured into its mouth. So again, the group of the Burgess Shale is really important. Now, all the factors that came into playing for the Burgess Shale, again it's the same group of looking at the origination, radiation and extinction eventually of organisms. There were changes in the ecosystem that then began to allow opening of different parts of the ecosystem to new types of organisms. These organisms came in quickly, they started evolving and radiating very successfully and then they'd drop off. And the drop off was, again, some kind of combination between predation, environmental change, and other factors that took place in the environment. The important thing for us is that it's the second example of nature running a very explicit and specific experiment, creating organisms that haven't been seen before or seen again. They were successful for a very short period of time, and then therefore they went extinct. The Cambrian fauna includes this group of the Burgess Shale fauna. And again, towards the end of that time period, as we move from the Cambrian into the Ordovician and then eventually into the Devonian, we see that all these faunas dropped off simultaneously. And they were probably all affected then by the same suite than included biological pressures on them, competition and predation. Reproductive strategies, other things that they been evolving and trying to use in the environment, along with changes in the environment in which they were living. Like the chemistries that were present, the, ocean water flows, if there were volcanic events. If there were ice sheets that were forming and of course, our old friend the meteor impacts. Always possible that these would come in randomly at different times, to reset the stage of evolution, on the sea floor at any given time. [MUSIC]
