Other Evidence for Evolution

Fossils and Fossilisation

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Ben Whitten

Learning Objectives

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What is a fossil?
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Fossils are essential for interpreting the past as they enable us to determine the structure of present and extinct organisms and some of their behaviours.


A fossil is any preserved trait of a previously living organism, for example, bones, teeth, tissue, footprints, dung, burrows, pollen.


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What conditions are required for fossilisation?
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The fossilisation of bones, teeth and shells (calcium-based fossilisation) requires several conditions:

  • Organism dies (usually near or within a body of water)

  • It is quickly covered by sediments (reduced incidence of scavenging or environmental damage)

  • Alkaline soil (acidic soils dissolves bones, teeth and shells)

  • Low oxygen environment (less bacterial activity, less decomposition)

  • Minerals replace the organic matter in bone

  • Bone is now considered stone, i.e. it’s fossilised


The fossilisation of body tissues (skin, muscle) requires different conditions compared to calcium-based fossilisation.

  • Organism dies (usually near or within a body of water)

  • Quickly covered by sediments (reduced incidence of scavenging or environmental damage)

  • Acidic soil (preserves soft tissue)

  • Low oxygen (less bacterial activity, less decomposition)

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Why is the fossil record incomplete?
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The fossil record is incomplete and therefore cannot represent the entire biodiversity of a time and location; reasons for incomplete fossil records include:


  • Conditions for fossilisation do not always occur (it’s a rare event)

  • Only a tiny proportion of fossils that exist have been discovered (remained buried or have already been destroyed, or are difficult to identify)

  • When fossils are found accurate dating can be difficult/problematic

  • Fossils of entire organisms are extremely rare; therefore, predictions have to be made in the reconstruction of whole organisms; this can lead to disagreements and controversy due to differing interpretations of fossil fragments available

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How else can we interpret the past?
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There are other ways to interpret the past, including artefacts which are manmade (hominin) objects, including stone tools, beads, cave paintings etc. and kitchen middens which is the site that was used for Hominin food preparation, containing bone, shells, seeds, charcoal etc.


How can fossils, artefacts and kitchen middens help us interpret the past? 


  • Fossils indicate the structure/anatomy of an organism, 

  • Artefacts tell us about culture, way of life and activities, and 

  • Kitchen middens inform us about the diet, what food they ate if they cooked their food etc.

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Fossils and Fossilisation
Dating Fossils
Relative Dating
Absolute Dating
Comparative Anatomy
Phylogenetic Trees
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