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Chapter 18 : Classification

Section 18-2: Modern Evolutionary Classification. Chapter 18 : Classification. Phylogeny – the study of how living and extinct organisms are related to one another Phylogentic systematics , or evolutionary classification

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Chapter 18 : Classification

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  1. Section 18-2: Modern Evolutionary Classification Chapter 18: Classification

  2. Phylogeny – the study of how living and extinct organisms are related to one another • Phylogenticsystematics, or evolutionary classification • Species grouped into larger categories reflecting lines of evolutionary descent • Organisms placed into higher taxa based on relationship – larger taxon, further common ancestor Evolutionary Classification

  3. Clade – a group of species tha includes a single common ancestor and all descendants of that ancestor, living and extinct Must be a monophyletic group – all species from common ancestor Cladistic analysis - how are clades related Clades

  4. Linked clades that illustrate how groups of organisms are related by showing how evolutionary lines (lineages) branched off from common ancestors Speciation causes an ancestral lineage to branch into 2 new lineages at a node Node is last point at which new lineages share common ancestor Cladograms

  5. “Root” represents common ancestor Building Cladograms

  6. Branching patterns shows degree of relatedness Building Cladograms

  7. Current hypotheses - evolutionary relationships among vertebrates Building CLadograms

  8. Cladistics focuses on derived characteristics – a trait that arose in the most recent ancestor of a particular lineage and was passed along to its descendants • Depends on level of grouping • Four limbs is a DC for clade Tetrapoda • Hair is a DC for clade Mammalia – not four limbs Derived Characteristics

  9. Clade Carnivora: shearing teeth (both) Clade Felidae: retractable claws (only lion) Derived Characteristics

  10. Absence of a trait is not a derived characteristic Whales and snakes have lost tetrapod characteristic of four limbs, but are not closely related Losing Traits

  11. Phylogeny of cat family Each DC defines a clade – a DC “lower” than the branch point for a clade is not derived for that clade Reading Cladograms

  12. Clade must be monophyletic Many traditional taxonomic groups form valid clades – Linnaen class Mammalia = clade Mammalia Birds and reptiles descend from common ancestor, but Linnaen class Reptilia does not include birds Clades and Traditional Taxonomic Groups

  13. According to cladistics a bird is a reptile Clades and Traditional Taxonomic Groups

  14. Homologies in genes used to determine evolutionary relationships • Changes in shared genes are derived characteristics • Using DNA makes evolutionary trees more accurate • Vultures, pandas DNA in Classification

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