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huelsenbeck14notes - Lecture 14 Monday April 6 2009 Fossils...

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Lecture 14 Monday, April 6, 2009 Fossils are preserved remains or traces of living organisms. Fossils are found in sedimentary rocks: Fossilization is not random. Hard parts — teeth, bones, shells — are most likely to be fossilized. Only under very rare conditions are soft body parts fossilized. Taphonomy is discussed in the laboratory on macroevolution. Trace fossils preserve some behaviors: Footprints, tracks, burrows, and underground nests occasionally provide information about behavior, e. g. stride length, gait, etc. Some recent fossils can yield DNA for analysis: DNA, primarily mitochondrial DNA, has been extracted from many fossils. The current upper limit is roughly 100,000 years. Whether DNA can be extracted from a fossil depends on the conditions of preservation and storage. Heat and humidity degrade DNA rapidly. Claims of sequencing DNA extracted from older specimens, including ancient bacteria, leaves, dinosaurs, and insects in amber, are not valid.
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