Plant fossil

A plant fossil is any preserved part of a plant that has long since died. Such fossils may be prehistoric impressions that are many millions of years old, or bits of charcoal that are only a few hundred years old.

Prehistoric plants are various groups of plants that lived before recorded history (before about 3500 BC).

Form taxa

Fossils of plants are very different from the fossils of animals, and this is in part a result of the different architecture of plants. Animals develop with a specific parts, and in both the young and adult animal, those parts exist in fixed numbers and locations. Even animals which undergo metamorphosis have only one head, and will emerge with a fixed body strucutre. By contrast, plants are continually producing new branches, leaves, and other parts throughout their lives. These parts may fall off without injuring the plant. Thus, plants fossils are often fragmentary pieces such as leaves, branches, or pollen.

Since a leaf, stem, spore, or seed may be found preserved without any physical connection to the plant from which it came, paleobotanists use form taxa (singular form taxon) to name and classify such fossils. When the true identity of such fossils is later discovered, the two form taxa may be merged. For example, in the 1960s fossil leaves called Archaeopteris (literally "ancient fern") were found attached to fossil wood of the tree Callixylon. The whole plant is now known to be a Devonian tree with fern-like leaves but with gymnosperm-like wood.

Some form taxa continue to exist even after their identity is determined. This is a mtter of convenience for identifying quickly which part was found as a fossil, especially which the fossil may come from more than one kind of plant. Leaves assigned to the form taxon Sphenopteris come from both ferns and from seed plants; it usually is not possible to determine from isolated fossils which group the leaves belong to.

Kinds of plant fossils

One of the most common kinds of plant fossils is a compression fossil, in which a leaf or flattened part of the plant has been pressed between layers of sediment. Also common are fossil pollen and spores from ancient lake beds, as well as charcoal. Less common, but economically more important, is coal from the plants of Carboniferous swamps.

One of the most spectacular of plant fossils is petrified wood.

Fossil groups of plants

Main articles: Evolutionary history of plants and List of extinct plants

Some plants have remained remarkedly unchanged throughout earth's geological time scale. Early ferns had developed by the Mississippian, conifers by the Pennsylvanian. Some plants of prehistory are the same ones around today and are thus living fossils, such as Ginkgo biloba and Sciadopitys verticillata. Other plants have changed radically, or have gone extinct entirely.

A few examples of prehistoric plants are:

Fossil of Lepidostrobus Variabilis, a very rare scale tree cone.

• Araucaria mirabilis
• Archaeopteris
• Calamites
• Cycads
• Glossopteris
• Horsetails
• Hymenaea protera
• Protosalvinia
• Whisk fern

See also

• Paleobotany
• Plant
• Prehistoric life
• Plant evolution

References

• Jurassic Park plants Plants that lived when dinosaurs roamed the earth.