Phylogeny

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Phylogeny metazoan origins Ch. 4 108-116, Ch.
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Metazoan origins (origin of multicellularity)

• how did multicellularity arise?
• why would multicellularity arise?
• (i.e. arent protists enough?)
• theories
• syncytial theory
• colonial theory
• polyphyletic origins of metazoa

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Syncytial theory

• metazoans arose from a multinucleated ciliate
• supporting evidence
• many protists are multinucleated
• similarities to simple larvae
• opposing evidence
• Most resembles flatworms
• Would imply flatworms predated sponges,
  cnidarians, ctenophores

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Colonial theory

• metazoans arose from a colonial flagellate
• Blastula from invagination of colony
• supporting evidence
• Flagellated sperm are common in metazoans
• Similarities between fossil embryos and some
  flagellated colonies
• Similarities between choanoflagellates and sponge
  choanocytes

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Colonial theory
?
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Classification

• Taxonomy as a way of showing relatedness
• Binomial nomenclature devised by Linnaeus in
  1758, in Systema Naturae
• Every organism has a unique name, given by the
  Genus and species names
• always italicize or underline these
• Genus is capitalized species in lower case
• Hierarchical Kingdom, Phylum, Class, Order,
  Family, Genus, species

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Phylogenetic terms

• Monophyletic includes ancestral species all
  descendents
• Polyphyletic includes species that arose from
  more than one immediate ancestor
• Paraphyletic includes species with same common
  ancestor, but not all descendents of that
  ancestor are included

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Phylogenetic terms

• Character trait or attribute (morphological,
  behavioral, etc.)
• Character state condition of a character
• e.g. character hair color
• character states brown, black, red
• Homology
• Convergent characters
• (analogous, homoplasies)

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Examples of Homologies
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Examples of Convergent characters
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Principle of parsimony

• William of Occam (or Ockham)
• Occams Razor
• given a choice between two explanations, choose
  the simplest
• dont make unnecessary leaps of logic