Because of the conditions necessary for their preservation, not all types of organisms that existed in the past have left fossils that can be retrieved.
Fossils are More Than Just Bones!
Many people typically think of fossils as bones. However, there are many different types of fossils and they are typically classified according to how they are formed. Fossils can be divided into two categories, fossilized body parts (bones, claws, teeth, skin, embryos, etc.) and fossilized traces, (which are footprints, nests, dung, tooth marks, etc.), all of which provide valuable clues about Earth’s past.
Category 1
Category 2
Trace Fossils
Trace fossils record the movements and behaviors of the organisms. Fossilized footprints, for example, can provide information about:
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Types of Fossils
Fossils are formed in many different ways, but most are formed when a plant or animal dies in a watery environment and is buried in mud and silt. Soft tissues such as muscle, fat, and skin quickly decompose leaving the hard bones or shells behind. Over time sediment builds over the top and hardens into rock. Erosion may wear away some of that rock to reveal a fossil.
Common Types of Fossils and How They Form:
Permineralization occurs when dissolved minerals carried by groundwater fill the tiny cellular spaces of plants and animals. The dissolved minerals crystallize and produce rocks in the shape of the animal or plant. This is the most common type of fossil people think of when they think about a fossil and this process typically preserves teeth, bones, shells, and wood.
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Carbonization is a process where only the residual carbon of the organism remains. In nature, this usually happens over time when the organism is subject to heat and pressure. Plant fossils are a very common example.
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Preserved remains record intact remains of animals, often including preserved skin, muscle, bone, hair, and internal organs. Fossils form when an entire organism becomes encased in material such as ice or volcanic ash or buried in peat bogs. Some organisms can be also preserved when they become trapped in tree resin that hardens into amber after the tree gets buried underground. Examples include insects, pollen, lizards, and frogs. This is a much rarer form of preservation than the other forms above.
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Natural casts form when flowing water removes all of the original bone or tissue, leaving just an impression in sediment. Minerals fill in the mold, recreating the original shape of the organism very common for marine organisms with shells.
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Topic Tips
- There are many different types of fossils.
- Fossils can be classified according to how they form.
- Some scientists classify fossils into 6 main categories that include, permineralized, casts, molds, carbonized, trace, and preserved.