• 1) How do we grapple with the bewildering diversity of animal life?

  • will emphasize common elements for each taxon: a) cladogram, b) key characters, c) habitat/habits, d) 'body plan' (symmetry, size, regionalization, limb number & form, skeleton, body cavities), e) locomotory & feeding structures, f) diversity of form

• 2) Two kinds of information help us infer the history of animal life:

  • distribution of characters (structures, genes) among living spp.
  • fossil record (not emphasized much in Z250), unfortunately it is very incomplete

• 3) "Characters" are sometimes divided into two groups:

  • homologous (present in a common ancestor) and
  • analogous (similar in form but not present in common ancestor)
  • although easy in principle, the distinction can be very difficult

• 4) Cladistic analysis is a formal method for inferring a phylogenetic tree (cladogram) based on distribution of characters among taxa

  • it uses a matrix of data (rows= taxa, column= characters)
  • the character state (presence/absence) is noted for each character
  • it assumes: 1) all organisms evolved from pre-existing ones by a simple branching process, and 2) convergence is rare
  • it determines the 'best' phylogenetic tree by finding the one that requires the fewest total character state changes

• 5) "Sister group" refers to a branch of a cladogram that lies adjacent to another branch (e.g., the Porifera is the sister group to all the remaining Metazoa); sister group is not synonymous with ancestor

• 6) Organisms are placed into a heirarchical (nested) classification: kingdom, phylum, class, order, family, genus, species, variety

  • ideally(!), a classification should not contradict a cladogram

• 7) DNA sequence data & computers have triggered a surge of interest in phylogenetic relations unseen since the turn of the century

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