Taxonomy

1. Taxonomy J.T. II Olivar, MAEd Faculty of Arts and Letters University of Santo Tomas

2. Outline of the Lecture • The Categorization of Earth’s Living Things • Constructing Evolutionary Histories: Classical Taxonomy and Cladistics

3. The Categorization of Earth’s Living Things • Taxonomic Classification and the Degree of Relatedness A. How to name a species • Specificity – each name must indicate one type of organism • Universality – Latin used to avoid confusion caused by common names • Recognizable by biologists of all nations • Binomial nomenclature • First names identifies groups of closely related species • Second name identifies specific species

4. B. Genus name • Indicates a group of species that share common features • “Relatedness” determines which species belong in which genus • Indicates a common ancestor at some time • Could be millions of years in the past • Systematics – branch of biology studying evolutionary history of organisms

5. C. Taxonomic System • Uses eight categories to catalog every identified organism • In order from most to least specific – species, genus, family, order, class, phylum, kingdom, domain • Taxon – organisms in each category

6. A Taxonomic Example: The Common House Cat • Genus: Felis – contains eight other living species • Family: Felidae – contains other 14 genera • Order: Carnivora – includes all meat-eating organisms • Kingdom: Animalia – includes all animals • Each level up the ladder includes more organisms

7. Constructing Evolutionary Histories: Classical Taxonomy and Cladistics • Classical Taxonomy Looks for Similarities • Classical taxonomy uses morphology to judge similarities • Compare physical form of fossil organisms with modern ones • Examine skull shape, teeth patterns (dentition), limb structure, etc. • Also compare geographic locations • Modern taxonomy includes relatedness of DNA and protein sequences

8. Obscuring the trail: Convergent evolution • Similar features may arise independently in response to environment • Homologies – common structures from shared ancestor • Analogy – structures that appear similar in appearance or structure without common ancestry • Convergent evolution • Separate evolutionary lines shaped in similar ways • Caused by similar environmental pressures

9. Another System for Interpreting the Evidence: Cladistics • Cladistics – method to establish relatedness • Core of modern phylogenetic work • Cladogram – diagram of lines of descent and order of branches • Seeks to answer – which organisms have most recent common ancestor

10. Cladistics employs shared ancestral and derived characteristics • Ancestral characters • Characteristics present in common ancestor • Ex: dorsal vertebral column in vertebrates • Derived character • Characteristic not shared by all organisms descended from common ancestor

11. Assumption • Closely related animals share more derived characteristics than those not closely related • Uses the hagfish as reference organism for all mammalian carnivores • Outgroup – does not share ancestral characters • Reference point for derived characters

12. Should Anything but Relatedness Matter in Classification? • Reconciling classical taxonomy with cladistics • Classical groupings uses more than evolutionary relationships • Considers many special qualities shared by organisms • Concerned with lines of descent and evolutionary relationships • Cladistics uses phylogeny to place organisms on tree • Concerned most with establishing lines of descent