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Lecture 18

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Western University
Biology 1001A
Tom Haffie

Biology 1001A Lecture 18: Macroevolution November 14, 2011  Next Time: Scan: Read text section 48.1 Recap:  Only synapomorphies are informative o Not all similarities are homologies o Not all homologies are synapomorphies  Homoplasy is misleading o Creates similarity between distantly related groups o Erases similarity between closely related groups  Most parsimonious tree (fewest evolutionary steps) is usually the best Phylogenies help classify life  Many currently-recognized ‘groups’ are not monophyletic… not ‘good’ groupings o Monophyletic Group: includes all descendants of the group’s most recent common ancestor. o Blue is better below Are “reptiles” monophyletic?  Purple Circle is good tree, least number of evolutionary steps  Reptiles are not monophyletic o Lizards and Crocodiles are most related with birds Other non-monophyletic groups  Prokaryotes are not true monophyletic o Related with Bacteria and Archea Patterns in Macroevolution  The fossil record  Mode and Temp of evolution  Evolutionary trends: changes in body size How old is that fossil?  Law of superposition o Layers at the bottom are older and layers at the top are younger in evolutionary time o Read rock strata from bottom to top o Relative order, not absolute dates o Radiometric Dating: parent decays to daughter isotope at predictable rate  Count half-life’s to determine actual age Fossil Record is incomplete and biased  Most species have never formed fossils  Biases in fossil record: o Temporal  Recent formations are more likely to be found, than older ones. Ancient rocks have been eroded, therefore, likely to find newer ones. o Taxonomic  Some parts are fossilized. Hard shells, bones, sturdy structures are most likely to be fossilized compared to worms, flowers and etc…
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