Chapter 16 Outline

EXTINCTIONS

• DISAPPEARANCE OF A TAXONOMIC GROUP
  • PSUEDOEXTINCTION - EVOLUTION OF A PARENT SPECIES INTO A DESCENDENT SPECIES
  • TERMINAL EXTINCTION - A SPECIES DIES OUT WITHOUT GIVING RISE TO A DESCENDENT SPECIES
• BACKGROUND EXTINCTIONS
  • EXTINCTION OF AN ISOLATED SPECIES
  • RESPONSIBLE FOR EXTINCTION OF MOST SPECIES (AS MANY AS 95%)
• MASS EXTINCTIONS
  • EXTINCTION OF LARGE NUMBERS & MANY TYPES OF SPECIES (& HIGHER TAXONOMIC GROUPS); EFFECTING THE BIOSPHERE GLOBALLY; AND OCCURRING IN A GEOLOGICALLY SHORT PERIOD OF TIME
  • BIG FIVE
    • Major mass extinction at the end of the PERMIAN
      • 52% OF ALL MARINE INVERTEBRATE FAMILIES & 96% OF MARINE INVERTEBRATE SPECIES WENT EXTINCT
    • Intermediate mass extinctions at or near the ends of the Ordovician, Devonian, Triassic & the CRETACEOUS
      • HUMANS HAVE CAUSED & ARE CAUSING AT AN ACCELERATING RATE THE EXTINCTION OF MANY ANIMAL & PLANT SPECIES
      • THE RESULT BY THE END OF THE NEXT CENTURY MAY BE A MASS EXTINCTION RIVALING THAT AT THE END OF THE PERMIAN
      • IS THERE ANY GUARANTEE THAT WE OURSELVES WILL SURVIVE SUCH A MASS EXTINCTION?

RESOLVING THE PAST

• INCOMPLETENESS OF THE FOSSIL RECORD: RESOLUTION
  • RESOLUTION IS THE DEGREE TO WHICH ONE CAN DISTINGUISH THE DETAIL OF THINGS
  • ROCKS RECORD IS INCOMPLETE - SEDIMENTS NOT DEPOSITED OR ERODED FOR EVERY INSTANCE OF TIME
    • 50-90% of time is not recorded by rocks
  • FOSSIL RECORD IS INCOMPLETE - FOSSILS OF EVERY ORGANISM ARE NOT PRESERVED
    • Less than 1% of all species that have lived on earth have probably been fossilized
    • Only ~10% of these have been found
  • THE POORER THE RESOLUTION, THE MORE ABRUPT ANY EXTINCTION EVENT LOOKS
  • SIGNOR-LIPPS EFFECT - THE CLOSER TO AN EXTINCTION BOUNDARY, THE LOWER THE PROBABILITY OF FINDING FOSSILS AND THE FEW THE NUMBER OF FOSSILS FOUND
    • Biostratigraphers extend the known range of a fossil to the nearest biostratigraphic boundary, making extinction events seem more sudden than they probably were
• TAXONOMIC LEVEL
  • FOSSILS OFTEN CANNOT BE IDENTIFIED AT THE SPECIES LEVEL
  • HIGHER TAXONOMIC LEVELS ABOVE SPECIES MIGHT LEAD TO COMPARING INCONGRUENT TAXA THAT ARE NOT TRULY EVOLUTIONARILY EQUIVALENT BECAUSE THERE IS NO EXACT DEFINITION FOR THESE HIGHER TAXONOMIC LEVELS

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