Index%20Fossils:%20Evolution%20and%20Biostratigraphy

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Index Fossils Evolution and Biostratigraphy
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Evolution

• Variations exist within a population
• Result from mutations and other genetic accidents
• Some variations are advantageous
• Others are not
• Some are neutral
• Natural Selection works on these variations
• Characteristics of population shift through time
  evolution

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What is Natural Selection?

• What phrase is commonly used to describe Natural
  Selection?
• Survival of the fittest
• What does it mean?
• Organisms best suited to the environment survive
  long enough to reproduce.
• Advantageous traits are passed on

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How do new species arise?

• When accumulated variations are great enough that
  some individuals within the population cannot
  interbreed, a new species has arisen.
• New species commonly arise in geographically or
  environmentally isolated areas.
• New species and original species may exist at
  same time

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Bio-Events

• First appearances of new species
• First appearances of new higher taxa
• Extinctions of species
• Mass extinctions of multiple taxa
• Bio-events are unique points in geologic time

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Index Fossils

• Some fossils are more useful than others for
  relative age determinations
• Fossils that are most useful are called INDEX
  FOSSILS
• What factors would maximize a fossils
  usefulness? (i.e., What makes a good index
  fossil?)

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What makes a good index fossil?

• Distinctive appearance/easy to recognize
• Short duration between first appearance and
  extinction (a.k.a. RANGE)
• Widespread geographic distribution (makes
  correlation possible across a wide area/multiple
  continents)

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Characteristics of Index Fossils

• Limited Stratigraphic Range
• Widespread Geographic Distribution
• Commonly Pelagic
• Or, tolerant of a wide variety of environments
  (found in many facies)

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Mile Markers in Deep Time

• Life is unique for each interval of time because
  of evolution and extinction
• Volcanos, earthquakes, mountains, types of rocks
  repeat throughout history
• Life does not repeat it is directional
• Therefore, we can place other Earth events in a
  framework based on fossils

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Mile Markers in Deep Time

• The fossil-based framework for Earth history is
  known as the GEOLOGIC TIME SCALE
• Units Eras, Periods, Epochs, Ages
• Boundaries between units are based on bio-events

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Index Fossils andInternational Stratotypes

• The Case of the Silurian Devonian Boundary

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Dr. Ivo Chlupác and Karlstejn
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Index Fossils and theSilurian - Devonian Boundary

• Graptolites
• Conodonts
• Chitinozoans
• Trilobites
• Brachiopods
• Cephalopods

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Definition ofthe S-D Boundary

• Stratotype Klonk, near Suchomasty, Czech
  Republic

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S-D GSSP

• GSSP Global Stratotype, Sequence and Point
• First appearance of Monograptus uniformis
  uniformis
• Bed 20
• Klonk, Czechia

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Preserving the Stratotype