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Paleontology
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- Palaeontology redirects here. For the scientific journal, see Palaeontology (journal).
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Paleontology (british: palaeontology)[derivation 1] is the study of prehistoric life.
Life on Earth has a rich history spanning at least , although large organisms have only existed for about . Life originated in the oceans and subsequently colonized the land, and was hit by a number of mass extinctions, at times wiping out as much as 95% of the biodiversity on Earth.
The more recent advent of humans does not typically fall under the remit of palaeontology: this is the realm of archaeology and anthropology. Organisms anatomically resembling modern humans have only existed for , and advanced culture for 10,000 years - a much shorter timescale than studied by palaeontology.
The remit of palaeontology also covers the search for traces of life on other worlds. For instance, it is very likely that life once existed on Mars, even if it doesn't today; thus palaeontology concerns itself with finding and identifying any traces it may have left.[1]
The evidence upon which palaeontologists base their conclusions is varied. Traditionally, it has centred on the (very incomplete) fossil record of organisms and the traces they left in sediments when they lived. However, modern analytical techniques have bolstered the available toolbox, and it is common to use biochemical, geochemical and genetic techniques to cast light on the affinity and behaviour of organims.
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[edit] Background
Modern paleontology sets ancient life in its context by studying how long-term physical changes of global geography paleogeography and climate paleoclimate have affected the evolution of life, how ecosystems have responded to these changes and have adapted the planetary environment in turn and how these mutual responses have affected today's patterns of biodiversity. Hence, paleontology overlaps with geology (the study of rocks and rock formations) as well as with botany, biology, zoology and ecology – fields concerned with life forms and how they interact.
The major subdivisions of paleontology include paleozoology (animals), paleobotany (plants) and micropaleontology (microfossils). Paleozoologists may specialise in invertebrate paleontology, which deals with animals without backbones or in vertebrate paleontology, dealing with fossils of animals with backbones, including fossil hominids (paleoanthropology). Micropaleontologists study microscopic fossils, including organic-walled microfossils whose study is called palynology.
There are many developing specialties such as paleobiology, paleoecology, ichnology (the study of tracks and burrows) and taphonomy (the study of what happens to organisms after they expire). Major areas of study include the correlation of rock strata with their geologic ages and the study of evolution of lifeforms.
Paleontology utilises the same classic binomial nomenclature scheme, devised for the biology of living things by the mid-18th century Swedish biologist Carolus Linnaeus and increasingly sets these species in a genealogical framework, showing their degrees of interrelatedness using the still somewhat controversial technique of 'cladistics'.
The primary economic importance of paleontology lies in the use of fossils to determine the age and nature of the rocks that contain them or the layers above or below. This information is vital to the mining industry and especially the petroleum industry. Simply looking at the fossils contained in a rock remains one of the fastest and most accurate means of telling how old that rock is.
Fossils were known by primitive humans and were sometimes identified correctly as the remains of ancient lifeforms. The organized study of paleontology dates from the late 18th century. For a more complete historical overview see the article History of paleontology.
[edit] Overview of the history of life
[edit] Sources of evidence
Evidence of the history of life relies upon physical, biological and chemical signatures preserved in rocks.
One difficulty is deducing the age of rocks. Relative dating (A was before B) is often sufficient for studying processes of evolution, but this is difficult for some time periods, because of the problems involved in matching up rocks of the same age across different continents.[2]
An absolute age can be placed on rocks containing radiogenic minerals such as uranium, by radiometric dating.
[edit] Body fossils
Fossils of organisms' bodies are usually the most informative type of evidence. Fossilisation is a rare event, and most fossils are destroyed by erosion or metamorphism before they can be observed. Hence the fossil record is very incomplete, increasingly so further back in time. Despite this, they are often adequate to illustrate the broader patterns of life's history.[3] There are also biases in the fossil record: different environments are more favourable to the preservation of different types of organism or parts of organisms.[4] Further, only the parts of organisms that were already mineralised are usually preserved, such as the shells of molluscs. Since most animal species are soft-bodied, they decay before they can become fossilised. As a result, although there are 30-plus phyla of living animals, two-thirds have never been found as fossils.[5]
Occasionally, unusual environments may preserve soft tissues. These allow palæontologists to examine the internal anatomy of animals which in other sediments are only represented by shells, spines, claws, etc – if they are preserved at all.
The sparseness of the fossil record means that organisms usually exist long before they are found in the fossil record - this is known as the Signor-Lipps effect.[6]
[edit] Trace fossils
Trace fossils consist mainly of tracks and burrows on and under what was then the seabed.
Trace fossils are particularly significant because they represent a data source that is not limited to animals with easily-fossilized hard parts, and which reflects organisms' behaviour. Also many traces date from significantly earlier than the body fossils of animals that are thought to have been capable of making them.[7] Whilst exact assignment of trace fossils to their makers is generally impossible, traces may provide the earliest physical evidence of the appearance of moderately complex animals (comparable to earthworms).
[edit] Geochemical observations
Geochemical observations may help deduce the global level of biological activity, or the affinity of a certain fossil.
[edit] Phylogenetic techniques
Cladistics is a technique for working out the “family tree” of a set of organisms. It works by the logic that, if groups B and C have more similarities to each other than either has to group A, then B and C are more closely related to each other than either is to A. Characters which are compared may be anatomical, such as the presence of a notochord, or molecular, by comparing sequences of DNA or protein. The result of a successful analysis is a hierarchy of clades – groups whose members are believed to share a common ancestor. The cladistic technique is sometimes fallible, as some features, such as wings or camera eyes, evolved more than once, convergently – this must be taken into account in analyses.
From the relationships, it may be possible to constrain the date that lineages first appeared. For instance, if fossils of B or C date to X million years ago and the calculated "family tree" says A was an ancestor of B and C, then A must have evolved more than X million years ago.
It is also possible to estimate how long ago two living clades diverged – i.e. approximately how long ago their last common acestor must have lived – by assuming that DNA mutations accumulate at a constant rate. These "molecular clocks", however, are fallible, and provide only a very approximate timing: they are not sufficiently precise and reliable for estimating when the groups that feature in the Cambrian explosion first evolved,[8] and estimates produced by different techniques vary by a factor of two.[9]
[edit] Genetics and Evo-devo
[edit] History of paleontology
[edit] See also
- Timeline of paleontology
- Important publications in paleontology
- Fossils
- History of paleontology
- Evolutionary history of life
- Geology
- Dinosaurs
- Radiometric dating
- Fossil collecting
- List of transitional fossils
- List of notable fossils
- List of fossil sites (with link directory)
[edit] References
- ^ from Greek: παλαιόν (palaeon) "old, ancient", ὄν, ὀντ- (on, ont-) "being, creature", and λόγος (logos) "speech, thought"
- ^ "{{{title}}}" . doi:.
- ^ e.g. Gehling, James (March 2001). "Burrowing below the basal Cambrian GSSP, Fortune Head, Newfoundland". Geological Magazine 138 (2): 213–218. doi:.
- ^ Benton MJ, Wills MA, Hitchin R (2000). "Quality of the fossil record through time". Nature 403 (6769): 534–7. doi:. PMID 10676959.
- Non-technical summary
- ^ Butterfield , N.J. (2003). "Exceptional Fossil Preservation and the Cambrian Explosion". Integrative and Comparative Biology 43 (1): 166–177. doi:. Retrieved on 2008-06-28.
- ^ Cowen, R.. History of Life. Blackwell Science.
- ^ Signor, P.W. (1982). "Sampling bias, gradual extinction patterns and catastrophes in the fossil record". Geological implications of impacts of large asteroids and comets on the earth: 291–296. Boulder, CO: Geological Society of America. A 84–25651 10–42. Retrieved on 2008-01-07.
- ^ e.g. Seilacher, A. (1994). "How valid is Cruziana Stratigraphy?" (PDF). International Journal of Earth Sciences 83 (4): 752–758. Retrieved on 2007-09-09.
- ^ Hug, L.A., and Roger, A.J. (2007). "The Impact of Fossils and Taxon Sampling on Ancient Molecular Dating Analyses". Molecular Biology and Evolution 24 (8): 889–1897.
- ^ Peterson, Kevin J., and Butterfield, N.J. (2005). "Origin of the Eumetazoa: Testing ecological predictions of molecular clocks against the Proterozoic fossil record". Proceedings of the National Academy of Sciences 102 (27): 9547. doi:. PMID 15983372.
[edit] External links
- Smithsonian's Paleobiology website: a good introduction
- University of California Museum of Paleontology FAQ About Paleontology
- The Paleontological Society
- The Palaeontological Association
- The Paleontology Portal
- International Palaeoentomological Society
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