THE FOSSIL RECORD
Key idea 1: fossil morphology is related to function and to particular modes of life,
and fossils my be used to interpret former environments.
Nb. You will need to look up the work you did on fossils last year to revise the
morphological features.
BIOLOGICAL CLASSIFICATION (example)
Kingdom
Phylum
Class
Order
Family
Genus
Species
Animalia
Chordata
Mammalia
Primates
Hominidae
Homo
Homo sapiens
Animals
Animals with backbones
Mammals
Monkeys, apes, man
Human, near human
Man
Wise man
Methods of Fossil Preservation
Usually only the hard parts of fossils remain, although soft parts may be recorded as
imprints or casts.
Preservation of intact hard parts – unusual as they are too fragile. May occur if plant or
animal is frozen.
Mummification: dehydration and drying up – found in arid climates
Preservation of insects in amber – resin secreted from trees
Bones preserved in peat or tar – no oxygen to assist decomposition
Carbonisation - - carbon content increased by loss of volatiles from organic compounds.
Soft body is preserved as an imprint.
Conversion of aragonite in shell to harder calcite
Petrifaction : minerals are deposited from water percolating through bones, shells etc.
Fossil hard parts replaced by silica, calcite, haematite, limonite or pyrite.
Mould and casts.
Complete the chart: Factors favouring preservation of fossils.
Favours
1. Rapid deposition: this stops
erosion & stops decay because it
excludes oxygen & protects
animals from scavengers
Limits
2. Marine environment: gives a
greater chance of formation
because there is more deposition
in this environment
3. Hard parts: material like calcium
carbonate left after decay of soft
parts is more likely to be
preserved
4. Small size: small organisms are
more quickly covered by sediment
5. Mature forms: these usually have
stronger skeletons/shells and so
have less chance of being broken
up
6. Low energy environment: fossils
more likely to be formed because
there is less chance of them being
moved & broken by currents
7. Large abundance: there is more
chance of them being preserved if
numbers are high
8. No metamorphism or deformation:
these processes usually destroy
fossils
Read the article (from Teaching Earth Sciences, Vol. 22, Pt 1) on ‘Exceptionally
preserved fossils and the history of life’, and answer the following questions:
1.
2.
3.
4.
5.
6.
7.
When was the Burgess Shale formed?
Why are the fossils of the Burgess Shale unusual?
What kind of conditions would produce these unusual fossils?
What is meant by a ‘Preservation window (Konservat-Lagerstatten)?
When was the Soom Shale formed?
What kinds of fossils are found in the Soom Shale?
Describe some of the high quality fossils found in the Soom Shale. How do these
fossils help us to understand the environment of the area at the time the fossils were
formed?
8. Look at Figure 1. Describe the distribution of Konservat-Lagerstatten in the geological
column.