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