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Fossil

For other uses of the term, see Fossil (disambiguation)

Fossilization is a rare occurrence, because natural materials tend to be recycled. In order for an organism to be fossilized, the remains need to be covered by sediment as soon as possible. There are different types of fossils, and fossilization processes.

The study of fossils is called paleontology.

Table of contents

1 Permineralization 2 Mould, cast and trace fossils 3 Resin fossils 4 Pseudofossils 5 Living fossils 6 See also

Permineralization

This process consists of literally turning an organism into stone. The organism gets covered by sediment soon after death, or after the initial decaying process. The degree in which the remains are decayed when covered, determines the later details of the fossil. Some fossils only consist of skeletal remains or teeth; other fossils contain traces of skin, feathers or even soft tissues. Once covered with sediment, these layers slowly compact to rock, after which the chemicals in the remains are slowly replaced with hard minerals.

Although the original chemical composition of the organism has entirely vanished, the mineralization process proceeds differently for different kinds of tissues, and microscopic details of internal bone structure may be preserved.

Mould, cast and trace fossils

If percolating water dissolves the remains of an organism, and thereby leaves a hole, this is called a mould fossil. If this hole is filled with more minerals, it is called a cast fossil. If the burial of the organism was rapid, then chances are that even impressions of soft tissues remain. Trace fossils are the remains of track ways, burrows, footprints, eggs and shells, nests and droppings. The latter, called coprolites, can give insight in the feeding behavior of animals and can therefore be of great importance.

Resin fossils

Smaller animals, insects, spiders and small lizards, can be trapped in resin (amber), which oozes from trees. These fossils can be found in sandstones or mudstones, or washed up on beaches, especially those around the Baltic Sea.

Pseudofossils

These are regular patterns in rocks, which are produced by naturally occurring processes. They can easily be mistaken for real fossils. These fossils can be formed by naturally formed 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 plant leaves.

Living fossils

A term used for any living species which closely resembles a species known from fossils, i.e., as if the fossil had "come to life". This can be a species known only from fossils until living representatives were discovered (the most famous example of this is the coelacanth fish, Latimeria chalumnae), or a single living species with no close relatives, but which is the sole survivor of a once large and widespread group in the fossil record (the best-known example of this is the ginkgo tree, Ginkgo biloba). Other "living fossils" are the nut clams (Ennucula superba), Lingula anatina, an inarticulate brachiopod, the tuatara lizard, the snout-nosed nasikabatrachus sahyadrensis frog, and the horseshoe crab (Limulus polyphemus).

See also

• Fossils and the geological timescale
• fossil fuels
• acritarchs
• transitional fossils

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