Chap26.BlackBoard.17Apr2024

Character Polarization Method

  • Stratigraphic Sequence:

    • Character states in older fossils are considered older.

    • Challenge: New fossil discoveries may reverse conclusions about character polarity.

    • Evidence Sources:

      • Methods 1, 2, and 3 are independent and validate each other.

Step 4: Build a Data Matrix

  • In the matrix, each species receives scores for all characters.

  • Requires careful study of organisms.

  • Outgroup Method:

    • Outgroup is scored as 0 for all characters.

    • Matching states in the ingroup are also coded as zero.

Step 5: Make Phylogenetic Tree

  • Use Data Set 1 to create a phylogenetic tree by hand.

  • Group species by shared derived character states.

Constructing the Tree (Pages 4-13)

  • One Character at a Time:

    • Circle the 1s in each column to identify shared characters.

    • Start with characters grouping the most species (4 and 8).

    • Ignore non-contributing characters (2, 5, 7) during initial grouping.

  • Adding Resolution:

    • Add more characters for finer resolution, focusing on those that group the most taxa (characters 3 and 10).

  • Tree Evolution:

    • Begin with characters that group the most species (4, 8).

    • After establishing base groups, add characters (1, 6, 9) based on the matrix.

    • Always ensure to add characters even if they do not alter the tree shape (5, 2, 7).

Important Terms

  • Node: Represents a common ancestor in the tree.

  • Internode: Area between nodes; can be hypothetically 'cut' and still maintain evolutionary relationships.

Character State Change/Transition

  • Indicates evolutionary steps; shown by short lines across branches.

  • State Change Representation:

    • 0 (older/ancestral state) to 1 (derived state).

Questions About Data Set 1

  • Identify the closest taxa to other taxa (A, B, C).

Fig. 22-19: Evolutionary Relationships

  • Examine relationships among various taxa:

    • Hawks, birds, ostriches, crocodiles, lizards, snakes, amphibians, mammals.

    • Key shared characteristics: Tetrapod limbs, amnion, feathers.

Data Set 2

  • Character number and species representation:

    • Example: Species A scores (1, 0, 1, 0, 1, 0, 0, 1);

    • Each character and taxon appears once on the tree.