Zoology 250 Lecture 2
DIVERSITY, PHYLOGENY, CLASSIFICATION
- 1) How do we grapple with the bewildering diversity of animal life?
- will emphasize common elements for each taxon [cladogram, key characters, habitat/habits, 'body plan' (size, symmetry, regionalization, number & form of limbs, type of skeleton, type & extent of coelom), locomotory & feeding structures]
- 2) Two kinds of information help us infer the history of animal life
- fossil record (not emphasized much in Z250)
- distribution of characters (structures, genes) among living spp.
- 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, 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 all organisms evolved from pre-existing ones by a simple branching process
- it determines the 'best' phylogenetic tree by finding the one that requires the fewest total character state changes
- 5) Organisms are placed into a heirarchical (nested) classification: kingdom, phylum, class, order, family, genus, species, varieties
- ideally(!), a classification should not contradict a cladogram
- 6) Some important characters: uni- vs. multicellular, radial vs. bilateral symmetry, diplo- vs triploblastic, acoelomate vs. pseudocoelomate vs. coelomate, spiral vs. radial cleavage
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Copyright © 1997 by A. Richard Palmer. All rights reserved.(revised Jan. 8, 1997)