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Lecture13_slides_23Sep11

Lecture13_slides_23Sep11 - Some important uses of fossils...

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1 Some important uses of fossils in evolutionary biology 1. Reconstructing biotic history 2. Calibration of molecular evolution; Minimum divergence dates 3. Intermediates as evidence of descent with modification 4. Reconstructing climatic history and ancient environments 5. Understanding tempo (rate) and mode (pattern) in evolution Birds Crocodiles 1. Biotic history: we can infer that extant species share a common ancestor in the past But . . . Birds Crocodiles Birds Crocodiles Fossils are critical to reconstructing biotic history! The “Fabric of Life” by Ray Troll includes extinct organisms! 2. Minimum divergence dates & calibrations Hurley I A et al. Proc. R. Soc. B 2007;274:489-498 ©2007 by The Royal Society Neopterygii
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2 3. Transitional fossils provide important evidence of descent with modification Eustenopteron 1881 Ichthyostega 1932 Tiktaalik 2005 Acanthostega Panderichthys 1987 1977-1994 4. Fossils are critical in reconstructing climate history & ancient environments Fossil and living pollen, Polemonium Oxygen isotope ratios of CaCO 3 in foraminifera are used to reconstruct temperatures Change and Stasis through the History of Life: 5. fossils tell us about tempo & mode in evolution The only illustration in On the Origin of Species (1859) Darwin saw a role for gradual change and splitting. Anagenesis (gradual change) Cladogenesis (splitting) Darwin looked to the fossil record for evidence & didn ʼ t see gradual change. If evolution occurs by natural selection, where are the transitional forms? Is there evidence of anagenesis? “The explanation lies, as I believe, in the extreme imperfection of the geological record .” (Darwin 1859).
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3 Transitional forms now abundant: e.g., theropod dinosaurs to modern birds bristles Sinornithosaurus filamentous structures Xiaotingia (July, 2011) And whales from ungulates… Is there anagenesis , or gradual small changes within lineages as Darwin hypothesized?
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