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Lecture 6

Lecture 6.pdf

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ANTH 203
Michael Bisson

Methods of Palaeontology and Dating Techniques Steps of Empirical Data Collection 1. Discovery Fieldwork to find and conserve fossils Fossils are as solid as flour paste Difficult to extract them without breaking them 2. Description Accurate descriptions are necessary for comparisons and step 3 3. Classification Identify your fossils either as members of known species or as new species Must take into account inherent variability within species 4. Identification of the evolutionary relationships of the fossils In other words, you have to relate them on a chronological line Classification A form of interpretation 2 basic kinds Early classifications based on physical similarity Phenetic classifications No conception of biological relations, just of physical similarities Modern classification designed to express evolutionary relationships Cladistic classifications Clade = a group of species that share a set of derived homologous characteristics Cladogram = tree diagram showing relationships between various lines Phenetic classification Numerical taxonomy Statistical comparisons of numerous physical traits Generate seriation of organism Tend to lump together creatures with similar adaptations Grouping together organisms that look alike Problems Convergent evolution Evolved traits that are similar because of similar function, but evolved from different structures They're only analogous traits e.g. Hummingbirds wings and hawk moths wings --> NOT SAME PHYLA Bird wings are a direct evolution from legs Hawk moths evolved from other things Cladistic classification Require selecting characteristics that are relevant to discovering evolutionary relationships Use of homologous traits Similar traits coming from ancestry Primitive traits Less useful Present in ancestral and descendant species Primitive = "appeared earlier" e.g. 5 fingers and toes Derived homologous traits Present in only some of the species descended from a common ancestor e.g. Structure of the big toe in humans Palaeontologists often disagree over cladistic relationships because the fossil record is often not complete Guidelines for Evaluating Conflicting Cladograms A proposed clade should be both simple and inclusive Avoiding unnecessary unexplained gaps Lumpers vs splitters debate Lumpers stress variation within species, and so they tend to define a smaller number of separate species Simple Splitters pay less attention to internal species variability, and thus tend to define a larger number of separate species More complex Clade should be based on authenticated and reliably dated data
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