FossilsFossils

What is a fossil?What is a fossil?A fossil is an impression, cast, original material or

track of any animal or plant that is preserved in rock by natural processes after the original organic material is transformed or removed.

Why is it important to study Why is it important to study fossils?fossils?

They are vital forunderstanding the evolutionary

history of life on earth as they provide direct evidence of

evolution and detailed information about the

ancestors of organisms.

A fossil may be:A fossil may be:

• an original skeleton or shell;

• a mold• a cast (material

that has replaced the once living thing)

• traces such as footprints, burrows or worm tubes

How are fossils formed?How are fossils formed?The remains of organisms or their imprint must be quickly buried so

weathering, decomposition or disruption from predators cannot

occur. Remains are preserved over time in rock strata (layers of

sediment). Minerals from ground water in the strata then replace the

bone remains.

Only a very small percentage of organisms become fossilised. Because the remains need to

be quickly covered with drifting sand, mud or water they are more often found in lakes,

swamps, caves or the sea bed.

Where do we find fossils?Where do we find fossils?

What conditions promote What conditions promote fossilisation?fossilisation?

• Hard body parts such as skeletal bones or exoskeletons

What conditions promote What conditions promote fossilisation?fossilisation?

• Rapid burial and/or lack of oxygen

• View the “Burying Bodies” animation at: http://www.abc.net.au/beasts/fossilfun/#

What are the modes of fossil What are the modes of fossil preservation for body fossils?preservation for body fossils?

True Form fossils are very rareThey are the originalunaltered material from theorganism (usually parts ofan organism, as teeth orshells) preserved incoatings of amber (sap) orunder frozen ground(If frozen soft tissue may bepreserved)

More on types of fossilsMore on types of fossils• Mold fossils –

reproduction of the inside or outside surface of a living thing. Hollow impression as if the organism was buried alive!

• Cast fossils – duplicate of the original organism; usually formed by replacement of the inside of living thing (bones) by minerals

Trace fossilsTrace fossils• Trace fossils are

impressions of passage (things left behind) of past organisms. Unlike molds and casts which are evidence or replicas of skeletal remains or body impressions, trace fossils are evidence of disturbance from an animal's activity such as resting, locomotion, or feeding.

• May include tracks,footprints, teethprints, feces, gallstones.