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Taxonomy Taxonomy Presentation Transcript

  • THE CLASSIFICATION OF LIVING ORGANISMS Taxonomy or Systematics: The study of classification ODWS Paul Billiet 2011
  • Why classify organisms?
    • Over a million species so far identified
    • Estimates of up to 30 million species on Earth
    • Need to organise this biodiversity
    • Systematics tells us about the patterns in nature, the way organisms are related and how they evolve
    • Systematics can be used to identify organisms that are important to us
    ODWS Paul Billiet 2011
  • The unit of taxonomy: The SPECIES
    • The term species has biological significance
    • Species form populations of individuals which may interbreed to form fully fertile offspring
    • Problem: Some species only use asexual reproduction or rarely use sexual reproduction
    ODWS Paul Billiet 2011
  • How taxonomy works
    • The aim is to group organisms according to their evolutionary relationship ( phylogeny )
    • Established by studying the phenotypes of living organisms or fossils
    • More recently DNA sequencing permits the comparisons of the genotypes
    • Uses characteristic features to group organisms together (e.g. all animals with feathers = Birds)
    • Taxonomists decide which are the most significant or "important" characteristic by the way it occurs in different groups of organisms.
    ODWS Paul Billiet 2011
  • Comparing phenotypes & genotypes
    • Taxonomists compare a new specimen with given characteristics:
    • morphology
    • anatomy
    • behaviour
    • embryology
    • protein structure
    • karyotypes
    • DNA sequence (DNA fingerprints)
    ODWS Paul Billiet 2011
  • Hierarchy of characters
    • Taxonomy uses many different characteristics to define a taxon
    • One character is not enough
    • The characteristics are grouped in a hierarchy.
    ODWS Paul Billiet 2011
  • Example
    • So having four legs with five toes is common to all land vertebrates and their fish ancestor
    • This would be used to group the animals we call tetrapods
    • Having a nerve cord running down the back is a feature common to all the tetrapods but also all the rest of the vertebrates
    • So it can be used to group all the vertebrates but not the tetrapods alone.
    ODWS Paul Billiet 2011 Acanthostega Lamprey
  • The pentadactyl limb
    • Classification led to comparisons of shape and form that gave rise to comparative anatomy
    • Comparative anatomists noticed that different species have similar structures used for different functions (e.g. the pentadactyle limb of terrestrial vertebrates)
    • These are called homologous structures.
    ODWS Paul Billiet 2011
  • The pendadactyle limb Lizard Human Frog Bat
  • Analogous or homologous characters
    • Even though the front legs of different mammals may look different they still use the same bones in their structure
    • The simplest explanation for this is that they all originated from a common ancestor, the ancestor of all mammals
    • This is called homology
    • As organisms evolved they split up and specialised in different ways of living
    • Their bodies changed in shape but they still retain some of their ancestors features
    ODWS Paul Billiet 2011
  • Homology in mammalian fore limbs ODWS Paul Billiet 2011
  • Analogous structures
    • Some structures may look very similar but have evolved independently
    • They are the product of natural selection on an organ adapting an organism to a particular niche
    ODWS Paul Billiet 2011 Thylacine Thylacinus cynocephalus Wolf Canis lupus