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Cladistics Making and testing hypotheses of relationship. 28 May 2015 Cladistics2108.ppt1
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HYPOTHESIS of relationship 28 May 2015 Cladistics2108.ppt2
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28 May 2015 Cladistics2108.ppt3 Cladistics Grouping by common descent. 3-taxon statement: A and B are more closely related to each other than either is to C.
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28 May 2015 Cladistics2108.ppt4 MONOPHYLETIC group(s): Grouping of species including all descendants of a common ancestor and the common ancestor.
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28 May 2015 Cladistics2108.ppt5 POLYPHYLETIC group [Linnaeus] states as follows: “On account of their warm bilocular heart, their lungs, their moveable eyelids, their hollow ears, penem intrantem feminam mammis lactantem, …” “I take the good old-fashioned ground that the whale is a fish… a whale is a spouting fish with a horizontal tail.” o Melville, H. 1851. Moby Dick, Chapter XXXII.
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28 May 2015 Cladistics2108.ppt6 POLYPHYLETIC group(s) Include one or more species not descended from the same ancestor as the other members. TO BE AVOIDED!!!!!!!
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28 May 2015 Cladistics2108.ppt7 BUT, lineages, true common ancestors, are unknown. ALL we really know are modern species. Fossil specimens could be ancestors, or extinct side branches, of the family tree.
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28 May 2015 Cladistics2108.ppt8 HOW TO RECOGNIZE A MONOPHYLETIC GROUP: Classification by shared derived characters only. primitive &/or convergent similarities will mislead.
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28 May 2015 Cladistics2108.ppt9 Shared derived character: = Homology = “Distinguishing character.” Trait, characteristic, or feature of a group found in every member of the group and not in any other group.
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28 May 2015 Cladistics2108.ppt10 Cladistics Avoids bias of researcher, authority. Grouping (classification) = scientific hypothesis. Testable by congruence of characters Repeatable.
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Cladistics Reading a cladogram X-axis Y-axis Line, line segment Node, branching point Line end 28 May 2015 Cladistics2108.ppt11
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Cladistics 28 May 2015 Cladistics2108.ppt12
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