5.7 Fossils and Cladograms

ima fail the test

Define Fossil. Tell me about them.

preserved remains of an organism or its activity

• Vast majority of fossils are made of rock and contain no organic material

• Rarely an organism’s actual tissue is preserved

What are examples of exceptions to the fossils not retaining organic material?

• amber

• ice

What is the 1^st Step of Fossilization?

Organism Dies and Its Body Tissue Decomposes

What is the 2^nd Step of Fossilization?

Remains are Covered with Layers of Sediment

What is the 3^rd Step of Fossilization?

Sedimentation Continues, Compressing Remains under Pressure

What is the 4^th Step of Fossilization?

Water Percolates through Remains, Causing All Organic Tissue to be Replaced by Minerals

What is the 5^th Step of Fossilization?

Geological Uplift and Erosion Bring Fossil to Surface where it Must be Discovered before It is Destroyed by Weather

What are the Limitations of Fossilization?

1. Fossilization is an Extremely Rare Event

2. Fossils Have to be Uncovered

3. Fossils are Rarely Found Complete

4. Soft Body Parts are Rarely Fossilized

Fossilization is an Extremely Rare Event

• most dead organisms are eaten or broken down by decomposers

• remains have to be quickly covered by sediment to fossilize; if not, weathering processes will destroy them

Fossils Have to be Uncovered

• “weathering” reveals fossils and palaeontologists have to be lucky to find them before they are destroyed

• there may be billions of fossils that are never discovered

Fossils are Rarely Found Complete

• most organisms are reconstructed from only a few fossilized bones or bone fragments

Soft Body Parts are Rarely Fossilized

• plants and invertebrates lack a bony skeleton so don’t tend to fossilize

• impressions of these organisms may be found

Define Comparative Anatomy

fossil record used to determine evolutionary relationship between extant (living) and extinct (no longer living) species

Define Cladograms

shows change in morphology over time

Evolutionary trees (cladograms) can be constructed with…

available fossil evidence

Explain Gradualism

Gradualism - change occurs very slowly and steadily over a long period of time

Since change is slow, theory of gradualism predicts existence of transitional forms in fossil record

Explain Punctuated Equilibrium

Punctuated Equilibrium - species do not change much over long periods of time

When change does occur, it is rapid and followed by a new equilibrium