The star-shaped holes (Catellocaula vallata) in this Upper Ordovician bryozoan represent a soft-bodied organism preserved by bioimmuration in the bryozoan skeleton.^[14]

Bioimmuration is a type of preservation in which a skeletal organism overgrows or otherwise subsumes another organism, preserving the latter, or an impression of it, within the skeleton.^[15] Usually it is a sessile skeletal organism, such as a bryozoan or an oyster, which grows along a substrate, covering other sessile encrusters. Sometimes the bioimmured organism is soft-bodied and is then preserved in negative relief as a kind of external mold. There are also cases where an organism settles on top of a living skeletal organism which grows upwards, preserving the settler in its skeleton. Bioimmuration is known in the fossil record from the Ordovician^[16] to the Recent.^[17]

To sum up, fossilization processes proceed differently for different kinds of tissues and under different kinds of conditions.

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Trace fossils

Main article: Trace fossil

Trace fossils are the remains of trackways, burrows, bioerosion, eggs and eggshells, nests, droppings and other types of impressions. Fossilized droppings, called coprolites, can give insight into the feeding behavior of animals and can therefore be of great importance.

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Microfossils

Microfossils about 1/2 mm each

Main article: Micropaleontology

'Microfossil' is a descriptive term applied to fossilized plants and animals whose size is just at or below the level at which the fossil can be analyzed by the naked eye. A commonly applied cut-off point between "micro" and "macro" fossils is 1 mm, although this is only an approximate guide. Microfossils may either be complete (or near-complete) organisms in themselves (such as the marine plankters foraminifera and coccolithophores) or component parts (such as small teeth or spores) of larger animals or plants. Microfossils are of critical importance as a reservoir of paleoclimate information, and are also commonly used by biostratigraphers to assist in the correlation of rock units.

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Resin fossils

A mosquito and a fly in Baltic amber that is between 40 and 60 million years old

Fossil resin (colloquially called amber) is a natural polymer found in many types of strata throughout the world, even the Arctic. The oldest fossil resin dates to the Triassic, though most dates to the Tertiary. The excretion of the resin by certain plants is thought to be an evolutionary adaptation for protection from insects and to seal wounds caused by damage elements. Fossil resin often contains other fossils called inclusions that were captured by the sticky resin. These include bacteria, fungi, other plants, and animals. Animal inclusions are usually small invertebrates, predominantly arthropods such as insects and spiders, and only extremely rarely a vertebrate such as a small lizard. Preservation of inclusions can be exquisite, including small fragments of DNA.

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Pseudofossils

This rock has a manganese dendrite which looks like a fossil plant. It is used as a pavement stone around swimming pool in Kona

Pseudofossils are visual patterns in rocks that are produced by naturally occurring geologic processes rather than biologic processes. They can easily be mistaken for real fossils. Some pseudofossils, such as dendrites, are formed by naturally occurring fissures in the rock that get filled up by percolating minerals. Other types of pseudofossils are kidney ore (round shapes in iron ore) and moss agates, which look like moss or plant leaves. Concretions, spherical or ovoid-shaped nodules found in some sedimentary strata, were once thought to be dinosaur eggs, and are often mistaken for fossils as well.

Ginkgo adiantoides Eocene fossil leaf from the Tranquille Shale of British Columbia, Canada.

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Living fossils

Main article: Living fossil

Living fossil is an informal term used for any living species which closely resembles a species known from fossils -- that is, it is as if the ancient fossil had "come to life."

This can be (a) a species or taxon known only from fossils until living representatives were discovered, such as the lobed-finned coelacanth, primitive monoplacophoran mollusk, and the Chinese maidenhair tree, or (b) a single living species with no close relatives, such as the New Caledonian Kagu, or the Sunbittern, or (c) a small group of closely-related species with no other close relatives, such as the oxygen-producing, primoidial stromatolite, inarticulate lampshell Lingula, many-chambered pearly Nautilus, rootless whisk fern, armored horseshoe crab, and dinosaur-like tuatara that are the sole survivors of a once large and widespread group in the fossil record.

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See also

• Bioerosion
• Elvis taxon
• Fossil collecting
• History of paleontology
• Ichnology
• Lazarus taxon
• List of transitional fossils
• List of fossils
• List of fossil sites
• Paleobiology
• Petrification
• Shark teeth
• Taphonomy
• Trace fossil

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References

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External links

Wikimedia Commons has media related to:

fossils

• The Virtual Fossil Museum throughout Time and Evolution
• Paleoportal, geology and fossils of the United States
• Palaeos, a multi-authored wiki encyclopedia on the history of life on Earth
• The Fossil Record, a complete listing of the families, orders, class and phyla found in the fossil record
• Bioerosion website, including fossil record