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    PaleontologyFrom Wikipedia, the free encyclopedia

    "Palaeontology" redirects here. For the scientific journal, see Palaeontology (journal).

    Paleontology or palaeontology (/pelntldi/, /pelntldi/ or /plntldi/, /plntldi/)is the scientific study of life existent prior to, and sometimes including, the start of the Holocene Epochroughly 11,700 years before present. It includes the study of fossils to determine organisms' evolution andinteractions with each other and their environments (their paleoecology). Paleontological observations havebeen documented as far back as the 5thcentury BC. The science became established in the 18thcentury as aresult of Georges Cuvier's work on comparative anatomy, and developed rapidly in the 19thcentury. Theterm itself originates from Greek , palaios, i.e. "old, ancient", , on (gen. ontos), i.e. "being,creature" and , logos, i.e. "speech, thought, study".[1]

    Paleontology lies on the border between biology and geology, but differs from archaeology in that itexcludes the study of morphologically modern humans. It now uses techniques drawn from a wide range ofsciences, including biochemistry, mathematics and engineering. Use of all these techniques has enabledpaleontologists to discover much of the evolutionary history of life, almost all the way back to when Earthbecame capable of supporting life, about 3,800 million years ago. As knowledge has increased,paleontology has developed specialised sub-divisions, some of which focus on different types of fossilorganisms while others study ecology and environmental history, such as ancient climates.

    Body fossils and trace fossils are the principal types of evidence about ancient life, and geochemicalevidence has helped to decipher the evolution of life before there were organisms large enough to leavebody fossils. Estimating the dates of these remains is essential but difficult: sometimes adjacent rock layersallow radiometric dating, which provides absolute dates that are accurate to within 0.5%, but more oftenpaleontologists have to rely on relative dating by solving the "jigsaw puzzles" of biostratigraphy.Classifying ancient organisms is also difficult, as many do not fit well into the Linnean taxonomy that iscommonly used for classifying living organisms, and paleontologists more often use cladistics to draw upevolutionary "family trees". The final quarter of the 20th century saw the development of molecularphylogenetics, which investigates how closely organisms are related by measuring how similar the DNA isin their genomes. Molecular phylogenetics has also been used to estimate the dates when species diverged,but there is controversy about the reliability of the molecular clock on which such estimates depend.

    Contents1 Overview

    1.1 A historical science1.2 Related sciences1.3 Subdivisions

    2 Sources of evidence2.1 Body fossils2.2 Trace fossils2.3 Geochemical observations

    3 Classifying ancient organisms4 Estimating the dates of organisms5 Overview of the history of life

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    A palaeontologist at work at JohnDay Fossil Beds National Monument

    The preparation of the fossilisedbones of Europasaurus holgeri

    5 Overview of the history of life5.1 Mass extinctions

    6 History of paleontology7 See also8 Notes9 References10 External links


    The simplest definition is "the study of ancient life".[2] Paleontologyseeks information about several aspects of past organisms: "theiridentity and origin, their environment and evolution, and what theycan tell us about the Earth's organic and inorganic past".[3]

    A historical science

    Paleontology is one of the historical sciences, along witharchaeology, geology, astronomy, cosmology, philology and historyitself.[4] This means that it aims to describe phenomena of the pastand reconstruct their causes.[5] Hence it has three main elements:description of the phenomena; developing a general theory about thecauses of various types of change; and applying those theories tospecific facts.[4]

    When trying to explain past phenomena, paleontologists and otherhistorical scientists often construct a set of hypotheses about thecauses and then look for a smoking gun, a piece of evidence thatindicates that one hypothesis is a better explanation than others.Sometimes the smoking gun is discovered by a fortunate accidentduring other research. For example, the discovery by Luis Alvarezand Walter Alvarez of an iridium-rich layer at theCretaceousTertiary boundary made asteroid impact and volcanismthe most favored explanations for the CretaceousPaleogeneextinction event.[5]

    The other main type of science is experimental science, which is often said to work by conductingexperiments to disprove hypotheses about the workings and causes of natural phenomena note that thisapproach cannot confirm a hypothesis is correct, since some later experiment may disprove it. However,when confronted with totally unexpected phenomena, such as the first evidence for invisible radiation,experimental scientists often use the same approach as historical scientists: construct a set of hypothesesabout the causes and then look for a "smoking gun".[5]

    Related sciences

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    Analyses using engineeringtechniques show that Tyrannosaurushad a devastating bite, but raisedoubts about how fast it could move.

    Paleontology lies on the boundary between biology and geology since paleontology focuses on the record ofpast life but its main source of evidence is fossils, which are found in rocks.[6] For historical reasonspaleontology is part of the geology departments of many universities, because in the 19th century and early20th century geology departments found paleontological evidence important for estimating the ages of rockswhile biology departments showed little interest.[7]

    Paleontology also has some overlap with archaeology, which primarily works with objects made by humansand with human remains, while paleontologists are interested in the characteristics and evolution of humansas organisms. When dealing with evidence about humans, archaeologists and paleontologists may worktogether for example paleontologists might identify animal or plant fossils around an archaeological site,to discover what the people who lived there ate; or they might analyze the climate at the time when the sitewas inhabited by humans.[8]

    In addition paleontology often uses techniques derived from othersciences, including biology, osteology, ecology, chemistry, physicsand mathematics.[2] For example, geochemical signatures from rocksmay help to discover when life first arose on Earth,[9] and analysesof carbon isotope ratios may help to identify climate changes andeven to explain major transitions such as the PermianTriassicextinction event.[10] A relatively recent discipline, molecularphylogenetics, often helps by using comparisons of different modernorganisms' DNA and RNA to re-construct evolutionary "familytrees"; it has also been used to estimate the dates of importantevolutionary developments, although this approach is controversialbecause of doubts about the reliability of the "molecular clock".[11]Techniques developed in engineering have been used to analyse howancient organisms might have worked, for example how fast Tyrannosaurus could move and how powerfulits bite was.[12][13] It is relatively commonplace to study fossils using X-ray microtomography[14] Acombination of paleontology, biology, and archaeology, paleoneurology is the study of endocranial casts (orendocasts) of species related to humans to learn about the evolution of human brains.[15]

    Paleontology even contributes to astrobiology, the investigation of possible life on other planets, bydeveloping models of how life may have arisen and by providing techniques for detecting evidence of life.[16]


    As knowledge has increased, paleontology has developed specialised subdivisions.[17] Vertebratepaleontology concentrates on fossils of vertebrates, from the earliest fish to the immediate ancestors ofmodern mammals. Invertebrate paleontology deals with fossils of invertebrates such as molluscs,arthropods, annelid worms and echinoderms. Paleobotany focuses on the study of fossil plants, buttraditionally includes the study of fossil algae and fungi. Palynology, the study of pollen and spores

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    This Marrella specimen illustrateshow clear and detailed the fossilsfrom the Burgess Shale lagersttteare.

    produced by land plants and protists, straddles the border between paleontology and botany, as it deals withboth living and fossil organisms. Micropaleontology deals with all microscopic fossil organisms, regardlessof the group to which they belong.[18]

    Instead of focusing on individual organisms, paleoecology examines the interactions between differentorganisms, such as their places in food chains, and the two-way interaction between organisms and theirenvironment.[19] One example is the development of oxygenic photosynthesis by bacteria, which hugelyincreased the productivity and diversity of ecosystems.[20] This also caused the oxygenation of theatmosphere. Together, these were a prerequisite for the evolution of the most complex eukaryotic cells, fromwhich all multicellular organisms are built.[21]

    Paleoclimatology, although sometimes treated as part of paleoecology,[18] focuses more on the history ofEarth's climate and the mechanisms that have changed it[22