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)
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