Saturday, November 14, 2009

Environmental determinants in selectivity in extinction

I was reading through the recent news of what is happening here at UW-Madison. While doing this I read an article about A sedimentary geologist, Dr. Shanan Peters, here at UW, winning an award for exceptional work in the field of sedimentary geology. This is not particularly newsworthy as this is a large university with an exceptionally good faculty.

But anyways it caught my attention, so I started to read a few of the articles written in the recent past by him. There was one that I found interesting and thought I would talk about here. Forewarning, I am not a geologist, I've never studied geology, so if I mess things up terribly I apologize ahead of time.

The one article I found interesting was titled, and was in printed in June of last year in the journal Nature.

What professor Peters looked at was the correlation in Paleozoic and modern marine fauna and the particular environment they lived in. In particular there was a strong correlation in the rock record between carbonate sediment environments (e.g. Limestone) and Paleozoic marine fauna in both the Paleozoic and later times. While at the same time there was no strong correlation between modern marine fauna and salisticlastic (e.g. sandstone, shale, etc...) sedimentary environments. This shows that in general maybe modern fauna were less specialized in the environment with which they could survive.

Who cares? What does this mean? Well in the Paleozoic there was many periods of high sea level with large parts of the continents under water, creating vast shallow seas. In these seas the fauna were creating large amounts of carbonate sediment which can be seen in the modern rock record. Most Paleozoic rocks are carbonate rocks. For instance where I sit now, in Madison Wisconsin, there is a shallow layer of Ordovician (Which is in the Paleozoic) carbonate rock as the bedrock. If you go to the Grand Canyon and look at the layers that represent the Paleozoic, there are layers of carbonate rock.

But in the Permian, which marks the end of the Paleozoic, the continents on the Earth joined together to form the super-continent Pangaea. This marked a drop in sea level and the draining of the shallow continental seas. This is seen in the rock record as a switch from carbonate rocks to sandstones and shale as we enter the Triassic. What else happened at the end of the Permian and the beginning of the Triassic, that's right the largest mass extinction in the history of the Earth. Because the previous Paleozoic fauna were more specialized in the environments in which they could survive, they would "naturally" have been selected to become extinct versus their counterparts that represent more modern fauna, which are less specialized.

Who cares? What does this mean? Besides the fact that I just like reading new things, I say this is another example of the explanatory power of Evolution and Natural Selection. Go Evolution!!!!

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