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Taxonomy. J.T. II Olivar, MAEd Faculty of Arts and Letters University of Santo Tomas. Outline of the Lecture. The Categorization of Earth’s Living Things Constructing Evolutionary Histories: Classical Taxonomy and Cladistics. The Categorization of Earth’s Living Things.

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J.T. II Olivar, MAEd

Faculty of Arts and Letters

University of Santo Tomas

outline of the lecture
Outline of the Lecture
  • The Categorization of Earth’s Living Things
  • Constructing Evolutionary Histories: Classical Taxonomy and Cladistics
the categorization of earth s living things
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

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

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

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
constructing evolutionary histories classical taxonomy and cladistics
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

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

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

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


    • 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

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