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Unformatted text preview: IB 200B Principals ofPhylogentic Systematics Spring 2008 MorphologicalData II - Ontogeny & Structure of Animals All members of monophytetic taxa share a common ancestor whose developmental pathway has been modified to produce descendant morphologies. But at what level or stage does morphology reveal patterns of relatedness? 1. Gametes- gastropod sperm - polyplacophoran eggs 2. Early cell division patterns- Spiral & Radial cleavagepatterns, polar lobes, unequalvs.equalcleavage. 3. Larval forms - Planula, trochophore, Veligers, Instars, direct development Hennig recognized the both the problems and advantages of ontogeny and coined term semaphoront- an organism at a particular stage in ontogeny. Also augmentation criteria. Study of links between development and evolutionwas relatively neglected until Ontogeny andPhylogeny was published by Gould in 1977.Gouldpresented his own ideas on heterochrony(evolutionary changes in the timing of development),presenting a unified view of neoteny, recapitulation, paedogenesis, retardation,progenesis, etc. Basic idea is that all heterochronyis a result of accelerationor retardationof different developmental processes (growth, sexual maturation, morphological changes, etc.), and that it is these processes that are important rather than their results. Ontogenyenters into our consideration of phylogeny at three levels: (1) Polarization of character state transformations (augmentation or primary). (2) Assessment of homology. (3) The recognition and exploration ofheterochronic (and heterotopic) patterns in the mgroup. In addition to heterochrony, hetertopic or changes in spatial patterning of ontogenetic processes is also important. While heterochrony is of interest in part because it can produce novelties constrainedalong ancestral ontogenies,and hence result in parallelism between ontogeny and phylogeny, heterotopy can produce new morphologies along trajectories differentfrom those that generated the forms of ancestors (Haeckel, 1866). Modificationof ontogenies involves both deletions and insertions. Nonterminal characters-- charactersthat occur in the ontogeneticsequence before a terminal character....
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This note was uploaded on 08/01/2008 for the course IB 200 taught by Professor Lindberg,mishler,will during the Spring '08 term at University of California, Berkeley.
- Spring '08