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Index Fossils: Evolution and Biostratigraphy

Index Fossils: Evolution and Biostratigraphy. 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

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Index Fossils: Evolution and Biostratigraphy

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  1. Index Fossils: Evolution and Biostratigraphy

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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 fossil’s usefulness? (i.e., What makes a good index fossil?)

  7. 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)

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

  9. 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

  10. 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

  11. Index Fossils andInternational Stratotypes The Case of the Silurian – Devonian Boundary

  12. Dr. Ivo Chlupáč and Karlstejn

  13. Index Fossils and theSilurian - Devonian Boundary • Graptolites * • Conodonts * • Chitinozoans * • Trilobites • Brachiopods • Cephalopods

  14. Definition ofthe S-D Boundary Stratotype: Klonk, near Suchomasty, Czech Republic

  15. S-D GSSP • GSSP = Global Stratotype, Sequence and Point • First appearance of Monograptus uniformis uniformis • Bed 20 • Klonk, Czechia

  16. Preserving the Stratotype

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