lecture21F06

lecture21F06 - Lecture 18: Macroevolution and the fossil...

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Lecture 18: Macroevolution and the fossil record Fossils kinds of fossils; easy” and “hard” fossils; more small fossils; geological time scale Stasis Punctuated equilibrium foraminifera; test; sediments; deep- sea drilling project Everything is gradual stickleback fish; varved deposits; foraminifera again Readings: read again Ch. 22.1, 25.1 Transition on a coarse scale reptile to mammal transition, therapsid, dentary bone Cool fossils Mazon Creek, Illinois, 300 MYA Pennsylvanian
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Fig. 25.4 There are many kinds of fossils A fossil is basically any kind of biological material or trace that was deposited at some time in the past. Some remains are unaltered, and some are altered by e.g. mineralization. An exceptional case is that of amber fossils.
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http://nautiloid.net/fossil s/sites/sylvania/sylvania .html Paleontologists prefer to find fossils that are weathered out of a loose matrix (surrounding material) if at all possible - getting fossils out of hard rock is hard work! Trilobite fossil in Ohio, weathered out - just needs picking up.
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Pliocene fossil clam showing microfossils in the matrix (material in which the large fossil is embedded) 1 large clam 5 or 6 of each kind of smaller clams hundreds of micro- fossils (magnified) There are more small fossils than large ones.
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Table 26.1 The geological time scale. Memorize the dates for the Eras . Also, read Fig. 26.7 on radiometric dating of fossils on your own.
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What we would like the fossil record to be is a sort of movie of the past, with a perfect view of everything that happened. We are never going to have such a perfect movie, because it would require a complete record for all times and all of the geographic range of the species of interest. But we do have a surprisingly good record in some cases, and one that is getting better each year as more of the fossil record is filled in.
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So, what can we learn from our amazing but incomplete fossil record movie? 1. Stasis - lack of change.
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lecture21F06 - Lecture 18: Macroevolution and the fossil...

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