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 Characteristics of population shift

through time = evolution

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

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

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

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?)

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)

Characteristics of Index Fossils

Limited Stratigraphic Range Widespread Geographic Distribution Commonly Pelagic Or, tolerant of a wide variety of

environments (found in many facies)

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

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

Index Fossils andInternational Stratotypes

The Case of the Silurian – Devonian Boundary

Dr. Ivo Chlupáč and Karlstejn

Index Fossils and theSilurian - Devonian Boundary

Graptolites * Conodonts * Chitinozoans * Trilobites Brachiopods Cephalopods

Definition ofthe S-D Boundary

Stratotype: Klonk, near Suchomasty, Czech Republic

S-D GSSP

GSSP = Global Stratotype, Sequence and Point

First appearance of Monograptus uniformis uniformis

Bed 20 Klonk, Czechia

Preserving the Stratotype