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Chapter 7. Animal Classification, Phylogeny, and Organization. Classification of Organisms. Systematics or taxonomy Study of the kinds and diversity of organisms and of the evolutionary relationships among them. A Taxonomic Hierarchy. Taxon

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chapter 7

Chapter 7

Animal Classification, Phylogeny, and Organization

classification of organisms
Classification of Organisms
  • Systematics or taxonomy
    • Study of the kinds and diversity of organisms and of the evolutionary relationships among them
a taxonomic hierarchy
A Taxonomic Hierarchy
  • Taxon
    • Any grouping of animals that shares a particular set of characteristics
  • Taxonomic categories
    • Hierarchically arranged (broader to specific)
    • Domain, kingdom, phylum, class, order, family, genus, species
    • Above species level there are no definitions for each category
  • Binomial system of nomenclature
  • International Code of Zoological Nomenclature
    • Homo sapiens (H. sapiens)
    • Other naming rules
      • See General Zoology Laboratory Manual (Exercise 6).
molecular approaches to animal systematics
Molecular Approaches to Animal Systematics
  • Relatedness of animals reflected in proteins and DNA.
    • Nuclear and mitochondrial DNA
    • Ribosomal RNA
domains and kingdoms
Domains and Kingdoms
  • Ribosomal RNA studies
    • Distant evolutionary relationships
    • Evolutionary conservation results in slow rates of change.
  • Three major lineages (Domains)
    • Eubacteria
      • Bacteria
    • Archaea
      • Extremophile microbes
    • Eukarya
      • Organisms with compartmentalized cells
      • Nuclear membranes mitochondrial and chloroplast membranes
  • Horizontal gene transfer (HGT) common in early history of life and makes base of tree net-like
animal systematics
Animal Systematics
  • Goal
    • Arrange animals into MONOPHYLETIC GROUPS using traits having a genetic basis and that can be measured (characters).
    • Single ancestral species and all descendants
  • Groupings reflecting insufficient knowledge
    • Members of a lineage found to have separate ancestry
      • Polyphyletic groups
    • Some, but not all, members of a lineage included
      • Paraphyletic group
approaches to animal systematics
Approaches to Animal Systematics
  • Evolutionary systematics
    • Traditional approach
    • Homologies useful in classification
    • Phylogenetic trees depict relationships, time, and abundance.
approaches to animal systematics1
Approaches to Animal Systematics
  • Phylogenetic systematics (cladistics)
    • Homologies of recent origin are most useful.
    • Ancestral characters
      • Common to all members of a group
      • Symplesiomorphies
    • Outgroup
      • Related group not included in study group
      • Used to help decide whether or not a character is ancestral or more recently derived
approaches to animal systematics2
Approaches to Animal Systematics
  • Phylogenetic systematics (continued)
    • Derived characters
      • Arisen since common ancestry with the outgroup
      • Synapomorphies
    • Clade
      • Related subset within a lineage
    • Cladogram
      • Depicts a hypothesis regarding monophyletic lineage

Figure 7.5 This hypothetical cladogram shows five taxa (1-5) and characters (A-H) used in deriving taxonomic relationships.

approaches to animal systematics3
Approaches to Animal Systematics
  • Phylogenetic species concept
    • Group of populations that have evolved independently of other groups of populations
    • Monophyletic
    • Share one or more synapomorphies
  • Hierarchical nesting
    • Cladograms represent nested groups that share synapomorphic characters.
    • Less inclusive nests contain closely related organisms.
compare figures 7 4 and 7 6
Compare figures 7.4 and 7.6
  • What kind of information is common to both representations?
  • What kind of information is present in figure 7.4 that is not in figure 7.6?
  • What kind of information is present in figure 7.6 that is not in figure 7.4?
  • How are the relationships between reptiles, birds, and mammals represented differently in the two figures?
  • How do the differences in question 4 reflect differing approaches of evolutionary systematics and phylogenetic systematics?

Table 7.2

  • Symmetry describes how parts of an animal are arranged around a point or axis.

Figure 7.7 Sponges display cell-aggregate organization and some sponges are asymmetrical (Monochora barbadensis).


Figure 7.9 Bilateral symmetry is accompanied by the formation of a distinct head (cephalization).

other patterns of organization
Other Patterns of Organization
  • Unicellular (cytoplasmic) level of organization
    • Protists (unicellular)
    • Sponges (cell aggregate)
  • Diploblastic organization
    • Ectoderm (outer cellular layer)
    • Endoderm (inner cellular layer)
    • Mesoglea (noncellular)
o ther patterns of organization
Other Patterns of Organization
  • Triploblastic Organization
    • Mesoderm
      • Third tissue later sandwiched between ectoderm and endoderm
      • Supportive, contractile, and blood cells
    • Body cavities often present
      • Organ development
      • Exchanges by diffusion
      • Storage
      • Hydrostatic skeletons
      • Elimination of wastes and reproductive products
      • Facilitate increased body size
figure 7 11 triploblastic organization
Figure 7.11 Triploblastic Organization.
  • Triploblastic acoelomate
    • Mesoderm forms solid mass.
  • Triploblastic pseudocoelomate
    • Body cavity not entirely lined by mesoderm.
    • Gut is not associated with muscle or connective tissue.
  • Triploblastic coelomate
    • Body cavity completely surrounded by mesoderm.
    • Mesenteries suspend visceral structures in body cavity.
higher animal taxonomy
Higher Animal Taxonomy
  • Animalia is monophyletic
    • Molecular and embryological evidence
  • Four phyla originated independently
  • Bilaterally symmetrical phyla
    • Protostome phyla
      • Spiral, determinate cleavage
      • Trochophore larval stage
      • Ecdysozoa
        • Molt a cuticle
      • Lophotrochozoa
    • Deuterostome phyla
      • Radial, indeterminate cleavage