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 and International Stratotypes
The Case of the Silurian – Devonian Boundary

12. Dr. Ivo Chlupáč and Karlstejn

13. Index Fossils and the Silurian - Devonian Boundary
Graptolites *
Conodonts *
Chitinozoans *
Trilobites
Brachiopods
Cephalopods

14. Definition of the 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