Thursday, November 29, 2007

Antarctic marine life and the origin of fossils

In the basement of the Crary lab where we work are several large tanks filled with water. In the water are animals that were collected by biologists from the sea floor and the waters of the McMurdo Sound. The temperature of the ocean here is only 28 F (-2 C) , which means it is below the freezing mark of fresh water. Nevertheless the ocean is teeming with life and has a quite elaborate food chain, with top predators, such as killer whales, and leopard seals and the Antarctic krill at the bottom. All these life forms have special adaptations to the cold. For example, fish, such as the Antarctic Cod, have a type of natural antifreeze in their blood which keeps it from freezing. In the photos you can see several strange-looking arthropods, star fish, bivalves and sponges.
There is a marked difference between the fossils we find in the cores and the biota of the modern McMurdo Sound. The difference is primarily caused by the fact that only skeletal body parts are preserved in the rock record. When animals die, their soft tissue decays, and only skeletal parts accumulate on the sea floor. A fossil assemblage therefore only represents a small portions of the actual fauna of the sea floor in the past. Paleontologists are aware of that and are specialists at knowing what is missing.

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