Paleontology

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"Palaeontology" redirects here. Paleontology_sentence_0

For the scientific journal, see Palaeontology (journal). Paleontology_sentence_1

Paleontology, also spelled palaeontology or palæontology (/ˌpeɪliɒnˈtɒlədʒi, ˌpæli-, -ən-/), is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene Epoch (roughly 11,700 years before present). Paleontology_sentence_2

It includes the study of fossils to classify organisms and study interactions with each other and their environments (their paleoecology). Paleontology_sentence_3

Paleontological observations have been documented as far back as the 5th century BCE. Paleontology_sentence_4

The science became established in the 18th century as a result of Georges Cuvier's work on comparative anatomy, and developed rapidly in the 19th century. Paleontology_sentence_5

The term itself originates from Greek παλαιός, palaios, "old, ancient", ὄν, on (gen. Paleontology_sentence_6

ontos), "being, creature", and λόγος, logos, "speech, thought, study". Paleontology_sentence_7

Paleontology lies on the border between biology and geology, but differs from archaeology in that it excludes the study of anatomically modern humans. Paleontology_sentence_8

It now uses techniques drawn from a wide range of sciences, including biochemistry, mathematics, and engineering. Paleontology_sentence_9

Use of all these techniques has enabled paleontologists to discover much of the evolutionary history of life, almost all the way back to when Earth became capable of supporting life, about 3.8 billion years ago. Paleontology_sentence_10

As knowledge has increased, paleontology has developed specialised sub-divisions, some of which focus on different types of fossil organisms while others study ecology and environmental history, such as ancient climates. Paleontology_sentence_11

Body fossils and trace fossils are the principal types of evidence about ancient life, and geochemical evidence has helped to decipher the evolution of life before there were organisms large enough to leave body fossils. Paleontology_sentence_12

Estimating the dates of these remains is essential but difficult: sometimes adjacent rock layers allow radiometric dating, which provides absolute dates that are accurate to within 0.5%, but more often paleontologists have to rely on relative dating by solving the "jigsaw puzzles" of biostratigraphy (arrangement of rock layers from youngest to oldest). Paleontology_sentence_13

Classifying ancient organisms is also difficult, as many do not fit well into the Linnaean taxonomy classifying living organisms, and paleontologists more often use cladistics to draw up evolutionary "family trees". Paleontology_sentence_14

The final quarter of the 20th century saw the development of molecular phylogenetics, which investigates how closely organisms are related by measuring the similarity of the DNA in their genomes. Paleontology_sentence_15

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. Paleontology_sentence_16

Overview Paleontology_section_0

The simplest definition of "paleontology" is "the study of ancient life". Paleontology_sentence_17

The field seeks information about several aspects of past organisms: "their identity and origin, their environment and evolution, and what they can tell us about the Earth's organic and inorganic past". Paleontology_sentence_18

Historical science Paleontology_section_1

William Whewell (1794–1866) classified paleontology as one of the historical sciences, along with archaeology, geology, astronomy, cosmology, philology and history itself: paleontology aims to describe phenomena of the past and to reconstruct their causes. Paleontology_sentence_19

Hence it has three main elements: description of past phenomena; developing a general theory about the causes of various types of change; and applying those theories to specific facts. Paleontology_sentence_20

When trying to explain the past, paleontologists and other historical scientists often construct a set of one or more hypotheses about the causes and then look for a "smoking gun", a piece of evidence that strongly accords with one hypothesis over any others. Paleontology_sentence_21

Sometimes researchers discover a "smoking gun" by a fortunate accident during other research. Paleontology_sentence_22

For example, the 1980 discovery by Luis and Walter Alvarez of iridium, a mainly extraterrestrial metal, in the CretaceousTertiary boundary layer made asteroid impact the most favored explanation for the Cretaceous–Paleogene extinction event – although debate continues about the contribution of volcanism. Paleontology_sentence_23

A complementary approach to developing scientific knowledge, experimental science, is often said to work by conducting experiments to disprove hypotheses about the workings and causes of natural phenomena. Paleontology_sentence_24

This approach cannot prove a hypothesis, since some later experiment may disprove it, but the accumulation of failures to disprove is often compelling evidence in favor. Paleontology_sentence_25

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 hypotheses about the causes and then look for a "smoking gun". Paleontology_sentence_26

Related sciences Paleontology_section_2

Paleontology lies between biology and geology since it focuses on the record of past life, but its main source of evidence is fossils in rocks. Paleontology_sentence_27

For historical reasons, paleontology is part of the geology department at many universities: in the 19th and early 20th centuries, geology departments found fossil evidence important for dating rocks, while biology departments showed little interest. Paleontology_sentence_28

Paleontology also has some overlap with archaeology, which primarily works with objects made by humans and with human remains, while paleontologists are interested in the characteristics and evolution of humans as a species. Paleontology_sentence_29

When dealing with evidence about humans, archaeologists and paleontologists may work together – 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 of habitation. Paleontology_sentence_30

In addition, paleontology often borrows techniques from other sciences, including biology, osteology, ecology, chemistry, physics and mathematics. Paleontology_sentence_31

For example, geochemical signatures from rocks may help to discover when life first arose on Earth, and analyses of carbon isotope ratios may help to identify climate changes and even to explain major transitions such as the Permian–Triassic extinction event. Paleontology_sentence_32

A relatively recent discipline, molecular phylogenetics, compares the DNA and RNA of modern organisms to re-construct the "family trees" of their evolutionary ancestors. Paleontology_sentence_33

It has also been used to estimate the dates of important evolutionary developments, although this approach is controversial because of doubts about the reliability of the "molecular clock". Paleontology_sentence_34

Techniques from engineering have been used to analyse how the bodies of ancient organisms might have worked, for example the running speed and bite strength of Tyrannosaurus, or the flight mechanics of Microraptor. Paleontology_sentence_35

It is relatively commonplace to study the internal details of fossils using X-ray microtomography. Paleontology_sentence_36

Paleontology, biology, archaeology, and paleoneurobiology combine to study endocranial casts (endocasts) of species related to humans to clarify the evolution of the human brain. Paleontology_sentence_37

Paleontology even contributes to astrobiology, the investigation of possible life on other planets, by developing models of how life may have arisen and by providing techniques for detecting evidence of life. Paleontology_sentence_38

Subdivisions Paleontology_section_3

As knowledge has increased, paleontology has developed specialised subdivisions. Paleontology_sentence_39

Vertebrate paleontology concentrates on fossils from the earliest fish to the immediate ancestors of modern mammals. Paleontology_sentence_40

Invertebrate paleontology deals with fossils such as molluscs, arthropods, annelid worms and echinoderms. Paleontology_sentence_41

Paleobotany studies fossil plants, algae, and fungi. Paleontology_sentence_42

Palynology, the study of pollen and spores produced by land plants and protists, straddles paleontology and botany, as it deals with both living and fossil organisms. Paleontology_sentence_43

Micropaleontology deals with microscopic fossil organisms of all kinds. Paleontology_sentence_44

Instead of focusing on individual organisms, paleoecology examines the interactions between different ancient organisms, such as their food chains, and the two-way interactions with their environments. Paleontology_sentence_45

For example, the development of oxygenic photosynthesis by bacteria caused the oxygenation of the atmosphere and hugely increased the productivity and diversity of ecosystems. Paleontology_sentence_46

Together, these led to the evolution of complex eukaryotic cells, from which all multicellular organisms are built. Paleontology_sentence_47

Paleoclimatology, although sometimes treated as part of paleoecology, focuses more on the history of Earth's climate and the mechanisms that have changed it – which have sometimes included evolutionary developments, for example the rapid expansion of land plants in the Devonian period removed more carbon dioxide from the atmosphere, reducing the greenhouse effect and thus helping to cause an ice age in the Carboniferous period. Paleontology_sentence_48

Biostratigraphy, the use of fossils to work out the chronological order in which rocks were formed, is useful to both paleontologists and geologists. Paleontology_sentence_49

Biogeography studies the spatial distribution of organisms, and is also linked to geology, which explains how Earth's geography has changed over time. Paleontology_sentence_50

Sources of evidence Paleontology_section_4

Body fossils Paleontology_section_5

Main article: Fossil Paleontology_sentence_51

Fossils of organisms' bodies are usually the most informative type of evidence. Paleontology_sentence_52

The most common types are wood, bones, and shells. Paleontology_sentence_53

Fossilisation is a rare event, and most fossils are destroyed by erosion or metamorphism before they can be observed. Paleontology_sentence_54

Hence the fossil record is very incomplete, increasingly so further back in time. Paleontology_sentence_55

Despite this, it is often adequate to illustrate the broader patterns of life's history. Paleontology_sentence_56

There are also biases in the fossil record: different environments are more favorable to the preservation of different types of organism or parts of organisms. Paleontology_sentence_57

Further, only the parts of organisms that were already mineralised are usually preserved, such as the shells of molluscs. Paleontology_sentence_58

Since most animal species are soft-bodied, they decay before they can become fossilised. Paleontology_sentence_59

As a result, although there are 30-plus phyla of living animals, two-thirds have never been found as fossils. Paleontology_sentence_60

Occasionally, unusual environments may preserve soft tissues. Paleontology_sentence_61

These lagerstätten allow paleontologists to examine the internal anatomy of animals that in other sediments are represented only by shells, spines, claws, etc. – if they are preserved at all. Paleontology_sentence_62

However, even lagerstätten present an incomplete picture of life at the time. Paleontology_sentence_63

The majority of organisms living at the time are probably not represented because lagerstätten are restricted to a narrow range of environments, e.g. where soft-bodied organisms can be preserved very quickly by events such as mudslides; and the exceptional events that cause quick burial make it difficult to study the normal environments of the animals. Paleontology_sentence_64

The sparseness of the fossil record means that organisms are expected to exist long before and after they are found in the fossil record – this is known as the Signor–Lipps effect. Paleontology_sentence_65

Trace fossils Paleontology_section_6

Main article: Trace fossil Paleontology_sentence_66

Trace fossils consist mainly of tracks and burrows, but also include coprolites (fossil feces) and marks left by feeding. Paleontology_sentence_67

Trace fossils are particularly significant because they represent a data source that is not limited to animals with easily fossilised hard parts, and they reflect organisms' behaviours. Paleontology_sentence_68

Also many traces date from significantly earlier than the body fossils of animals that are thought to have been capable of making them. Paleontology_sentence_69

Whilst exact assignment of trace fossils to their makers is generally impossible, traces may for example provide the earliest physical evidence of the appearance of moderately complex animals (comparable to earthworms). Paleontology_sentence_70

Geochemical observations Paleontology_section_7

Main article: Geochemistry Paleontology_sentence_71

Geochemical observations may help to deduce the global level of biological activity at a certain period, or the affinity of certain fossils. Paleontology_sentence_72

For example, geochemical features of rocks may reveal when life first arose on Earth, and may provide evidence of the presence of eukaryotic cells, the type from which all multicellular organisms are built. Paleontology_sentence_73

Analyses of carbon isotope ratios may help to explain major transitions such as the Permian–Triassic extinction event. Paleontology_sentence_74

Classifying ancient organisms Paleontology_section_8

Main articles: Biological classification, Cladistics, Phylogenetic nomenclature, and Evolutionary taxonomy Paleontology_sentence_75

Naming groups of organisms in a way that is clear and widely agreed is important, as some disputes in paleontology have been based just on misunderstandings over names. Paleontology_sentence_76

Linnaean taxonomy is commonly used for classifying living organisms, but runs into difficulties when dealing with newly discovered organisms that are significantly different from known ones. Paleontology_sentence_77

For example: it is hard to decide at what level to place a new higher-level grouping, e.g. genus or family or order; this is important since the Linnaean rules for naming groups are tied to their levels, and hence if a group is moved to a different level it must be renamed. Paleontology_sentence_78

Paleontologists generally use approaches based on cladistics, a technique for working out the evolutionary "family tree" of a set of organisms. Paleontology_sentence_79

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. Paleontology_sentence_80

Characters that are compared may be anatomical, such as the presence of a notochord, or molecular, by comparing sequences of DNA or proteins. Paleontology_sentence_81

The result of a successful analysis is a hierarchy of clades – groups that share a common ancestor. Paleontology_sentence_82

Ideally the "family tree" has only two branches leading from each node ("junction"), but sometimes there is too little information to achieve this and paleontologists have to make do with junctions that have several branches. Paleontology_sentence_83

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. Paleontology_sentence_84

Evolutionary developmental biology, commonly abbreviated to "Evo Devo", also helps paleontologists to produce "family trees", and understand fossils. Paleontology_sentence_85

For example, the embryological development of some modern brachiopods suggests that brachiopods may be descendants of the halkieriids, which became extinct in the Cambrian period. Paleontology_sentence_86

Estimating the dates of organisms Paleontology_section_9

Main article: Geochronology Paleontology_sentence_87

Paleontology seeks to map out how living things have changed through time. Paleontology_sentence_88

A substantial hurdle to this aim is the difficulty of working out how old fossils are. Paleontology_sentence_89

Beds that preserve fossils typically lack the radioactive elements needed for radiometric dating. Paleontology_sentence_90

This technique is our only means of giving rocks greater than about 50 million years old an absolute age, and can be accurate to within 0.5% or better. Paleontology_sentence_91

Although radiometric dating requires very careful laboratory work, its basic principle is simple: the rates at which various radioactive elements decay are known, and so the ratio of the radioactive element to the element into which it decays shows how long ago the radioactive element was incorporated into the rock. Paleontology_sentence_92

Radioactive elements are common only in rocks with a volcanic origin, and so the only fossil-bearing rocks that can be dated radiometrically are a few volcanic ash layers. Paleontology_sentence_93

Consequently, paleontologists must usually rely on stratigraphy to date fossils. Paleontology_sentence_94

Stratigraphy is the science of deciphering the "layer-cake" that is the sedimentary record, and has been compared to a jigsaw puzzle. Paleontology_sentence_95

Rocks normally form relatively horizontal layers, with each layer younger than the one underneath it. Paleontology_sentence_96

If a fossil is found between two layers whose ages are known, the fossil's age must lie between the two known ages. Paleontology_sentence_97

Because rock sequences are not continuous, but may be broken up by faults or periods of erosion, it is very difficult to match up rock beds that are not directly next to one another. Paleontology_sentence_98

However, fossils of species that survived for a relatively short time can be used to link up isolated rocks: this technique is called biostratigraphy. Paleontology_sentence_99

For instance, the conodont Eoplacognathus pseudoplanus has a short range in the Middle Ordovician period. Paleontology_sentence_100

If rocks of unknown age are found to have traces of E. pseudoplanus, they must have a mid-Ordovician age. Paleontology_sentence_101

Such index fossils must be distinctive, be globally distributed and have a short time range to be useful. Paleontology_sentence_102

However, misleading results are produced if the index fossils turn out to have longer fossil ranges than first thought. Paleontology_sentence_103

Stratigraphy and biostratigraphy can in general provide only relative dating (A was before B), which is often sufficient for studying evolution. Paleontology_sentence_104

However, this is difficult for some time periods, because of the problems involved in matching up rocks of the same age across different continents. Paleontology_sentence_105

Family-tree relationships may also help to narrow down the date when lineages first appeared. Paleontology_sentence_106

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. Paleontology_sentence_107

It is also possible to estimate how long ago two living clades diverged – i.e. approximately how long ago their last common ancestor must have lived – by assuming that DNA mutations accumulate at a constant rate. Paleontology_sentence_108

These "molecular clocks", however, are fallible, and provide only a very approximate timing: for example, they are not sufficiently precise and reliable for estimating when the groups that feature in the Cambrian explosion first evolved, and estimates produced by different techniques may vary by a factor of two. Paleontology_sentence_109

History of life Paleontology_section_10

Main article: Evolutionary history of life Paleontology_sentence_110

Further information: Timeline of evolutionary history of life Paleontology_sentence_111

Earth formed about  million years ago and, after a collision that formed the Moon about 40 million years later, may have cooled quickly enough to have oceans and an atmosphere about  million years ago. Paleontology_sentence_112

There is evidence on the Moon of a Late Heavy Bombardment by asteroids from million years ago. Paleontology_sentence_113

If, as seems likely, such a bombardment struck Earth at the same time, the first atmosphere and oceans may have been stripped away. Paleontology_sentence_114

Paleontology traces the evolutionary history of life back to over  million years ago, possibly as far as  million years ago. Paleontology_sentence_115

The oldest clear evidence of life on Earth dates to  million years ago, although there have been reports, often disputed, of fossil bacteria from  million years ago and of geochemical evidence for the presence of life  million years ago. Paleontology_sentence_116

Some scientists have proposed that life on Earth was "seeded" from elsewhere, but most research concentrates on various explanations of how life could have arisen independently on Earth. Paleontology_sentence_117

For about 2,000 million years microbial mats, multi-layered colonies of different bacteria, were the dominant life on Earth. Paleontology_sentence_118

The evolution of oxygenic photosynthesis enabled them to play the major role in the oxygenation of the atmosphere from about  million years ago. Paleontology_sentence_119

This change in the atmosphere increased their effectiveness as nurseries of evolution. Paleontology_sentence_120

While eukaryotes, cells with complex internal structures, may have been present earlier, their evolution speeded up when they acquired the ability to transform oxygen from a poison to a powerful source of metabolic energy. Paleontology_sentence_121

This innovation may have come from primitive eukaryotes capturing oxygen-powered bacteria as endosymbionts and transforming them into organelles called mitochondria. Paleontology_sentence_122

The earliest evidence of complex eukaryotes with organelles (such as mitochondria) dates from  million years ago. Paleontology_sentence_123

Multicellular life is composed only of eukaryotic cells, and the earliest evidence for it is the Francevillian Group Fossils from  million years ago, although specialisation of cells for different functions first appears between  million years ago (a possible fungus) and  million years ago (a probable red alga). Paleontology_sentence_124

Sexual reproduction may be a prerequisite for specialisation of cells, as an asexual multicellular organism might be at risk of being taken over by rogue cells that retain the ability to reproduce. Paleontology_sentence_125

The earliest known animals are cnidarians from about  million years ago, but these are so modern-looking that must be descendants of earlier animals. Paleontology_sentence_126

Early fossils of animals are rare because they had not developed mineralised, easily fossilized hard parts until about  million years ago. Paleontology_sentence_127

The earliest modern-looking bilaterian animals appear in the Early Cambrian, along with several "weird wonders" that bear little obvious resemblance to any modern animals. Paleontology_sentence_128

There is a long-running debate about whether this Cambrian explosion was truly a very rapid period of evolutionary experimentation; alternative views are that modern-looking animals began evolving earlier but fossils of their precursors have not yet been found, or that the "weird wonders" are evolutionary "aunts" and "cousins" of modern groups. Paleontology_sentence_129

Vertebrates remained a minor group until the first jawed fish appeared in the Late Ordovician. Paleontology_sentence_130

The spread of animals and plants from water to land required organisms to solve several problems, including protection against drying out and supporting themselves against gravity. Paleontology_sentence_131

The earliest evidence of land plants and land invertebrates date back to about  million years ago and  million years ago respectively. Paleontology_sentence_132

Those invertebrates, as indicated by their trace and body fossils, were shown to be arthropods known as euthycarcinoids. Paleontology_sentence_133

The lineage that produced land vertebrates evolved later but very rapidly between  million years ago and  million years ago; recent discoveries have overturned earlier ideas about the history and driving forces behind their evolution. Paleontology_sentence_134

Land plants were so successful that their detritus caused an ecological crisis in the Late Devonian, until the evolution of fungi that could digest dead wood. Paleontology_sentence_135

During the Permian period, synapsids, including the ancestors of mammals, may have dominated land environments, but this ended with the Permian–Triassic extinction event  million years ago, which came very close to wiping out all complex life. Paleontology_sentence_136

The extinctions were apparently fairly sudden, at least among vertebrates. Paleontology_sentence_137

During the slow recovery from this catastrophe a previously obscure group, archosaurs, became the most abundant and diverse terrestrial vertebrates. Paleontology_sentence_138

One archosaur group, the dinosaurs, were the dominant land vertebrates for the rest of the Mesozoic, and birds evolved from one group of dinosaurs. Paleontology_sentence_139

During this time mammals' ancestors survived only as small, mainly nocturnal insectivores, which may have accelerated the development of mammalian traits such as endothermy and hair. Paleontology_sentence_140

After the Cretaceous–Paleogene extinction event  million years ago killed off all the dinosaurs except the birds, mammals increased rapidly in size and diversity, and some took to the air and the sea. Paleontology_sentence_141

Fossil evidence indicates that flowering plants appeared and rapidly diversified in the Early Cretaceous between  million years ago and  million years ago. Paleontology_sentence_142

Their rapid rise to dominance of terrestrial ecosystems is thought to have been propelled by coevolution with pollinating insects. Paleontology_sentence_143

Social insects appeared around the same time and, although they account for only small parts of the insect "family tree", now form over 50% of the total mass of all insects. Paleontology_sentence_144

Humans evolved from a lineage of upright-walking apes whose earliest fossils date from over  million years ago. Paleontology_sentence_145

Although early members of this lineage had chimp-sized brains, about 25% as big as modern humans', there are signs of a steady increase in brain size after about  million years ago. Paleontology_sentence_146

There is a long-running debate about whether modern humans are descendants of a single small population in Africa, which then migrated all over the world less than 200,000 years ago and replaced previous hominine species, or arose worldwide at the same time as a result of interbreeding. Paleontology_sentence_147

Mass extinctions Paleontology_section_11

Main article: Mass extinction Paleontology_sentence_148

Life on earth has suffered occasional mass extinctions at least since  million years ago. Paleontology_sentence_149

Despite their disastrous effects, mass extinctions have sometimes accelerated the evolution of life on earth. Paleontology_sentence_150

When dominance of an ecological niche passes from one group of organisms to another, this is rarely because the new dominant group outcompetes the old, but usually because an extinction event allows new group to outlive the old and move into its niche. Paleontology_sentence_151

The fossil record appears to show that the rate of extinction is slowing down, with both the gaps between mass extinctions becoming longer and the average and background rates of extinction decreasing. Paleontology_sentence_152

However, it is not certain whether the actual rate of extinction has altered, since both of these observations could be explained in several ways: Paleontology_sentence_153

Paleontology_unordered_list_0

  • The oceans may have become more hospitable to life over the last 500 million years and less vulnerable to mass extinctions: dissolved oxygen became more widespread and penetrated to greater depths; the development of life on land reduced the run-off of nutrients and hence the risk of eutrophication and anoxic events; marine ecosystems became more diversified so that food chains were less likely to be disrupted.Paleontology_item_0_0
  • Reasonably complete fossils are very rare: most extinct organisms are represented only by partial fossils, and complete fossils are rarest in the oldest rocks. So paleontologists have mistakenly assigned parts of the same organism to different genera, which were often defined solely to accommodate these finds – the story of Anomalocaris is an example of this. The risk of this mistake is higher for older fossils because these are often unlike parts of any living organism. Many "superfluous" genera are represented by fragments that are not found again, and these "superfluous" genera are interpreted as becoming extinct very quickly.Paleontology_item_0_1

Biodiversity in the fossil record, which is Paleontology_sentence_154

Paleontology_description_list_1

  • Paleontology_item_1_2
    • "the number of distinct genera alive at any given time; that is, those whose first occurrence predates and whose last occurrence postdates that time"Paleontology_item_1_3

shows a different trend: a fairly swift rise from million years ago, a slight decline from million years ago, in which the devastating Permian–Triassic extinction event is an important factor, and a swift rise from  million years ago to the present. Paleontology_sentence_155

History Paleontology_section_12

Main article: History of paleontology Paleontology_sentence_156

Further information: Timeline of paleontology Paleontology_sentence_157

Although paleontology became established around 1800, earlier thinkers had noticed aspects of the fossil record. Paleontology_sentence_158

The ancient Greek philosopher Xenophanes (570–480 BCE) concluded from fossil sea shells that some areas of land were once under water. Paleontology_sentence_159

During the Middle Ages the Persian naturalist Ibn Sina, known as Avicenna in Europe, discussed fossils and proposed a theory of petrifying fluids on which Albert of Saxony elaborated in the 14th century. Paleontology_sentence_160

The Chinese naturalist Shen Kuo (1031–1095) proposed a theory of climate change based on the presence of petrified bamboo in regions that in his time were too dry for bamboo. Paleontology_sentence_161

In early modern Europe, the systematic study of fossils emerged as an integral part of the changes in natural philosophy that occurred during the Age of Reason. Paleontology_sentence_162

In the Italian Renaissance, Leonardo Da Vinci made various significant contributions to the field as well depicted numerous fossils. Paleontology_sentence_163

Leonardo's contributions are central to the history of paleontology because he established a line of continuity between the two main branches of paleontology – ichnology and body fossil paleontology. Paleontology_sentence_164

He identified the following: Paleontology_sentence_165

Paleontology_ordered_list_2

  1. The biogenic nature of ichnofossils, i.e. ichnofossils were structures left by living organisms;Paleontology_item_2_4
  2. The utility of ichnofossils as paleoenvironmental tools – certain ichnofossils show the marine origin of rock strata;Paleontology_item_2_5
  3. The importance of the neoichnological approach – recent traces are a key to understanding ichnofossils;Paleontology_item_2_6
  4. The independence and complementary evidence of ichnofossils and body fossils – ichnofossils are distinct from body fossils, but can be integrated with body fossils to provide paleontological informationPaleontology_item_2_7

At the end of the 18th century Georges Cuvier's work established comparative anatomy as a scientific discipline and, by proving that some fossil animals resembled no living ones, demonstrated that animals could become extinct, leading to the emergence of paleontology. Paleontology_sentence_166

The expanding knowledge of the fossil record also played an increasing role in the development of geology, particularly stratigraphy. Paleontology_sentence_167

The first half of the 19th century saw geological and paleontological activity become increasingly well organised with the growth of geologic societies and museums and an increasing number of professional geologists and fossil specialists. Paleontology_sentence_168

Interest increased for reasons that were not purely scientific, as geology and paleontology helped industrialists to find and exploit natural resources such as coal. Paleontology_sentence_169

This contributed to a rapid increase in knowledge about the history of life on Earth and to progress in the definition of the geologic time scale, largely based on fossil evidence. Paleontology_sentence_170

In 1822 Henri Marie Ducrotay de Blainville, editor of Journal de Physique, coined the word "palaeontology" to refer to the study of ancient living organisms through fossils. Paleontology_sentence_171

As knowledge of life's history continued to improve, it became increasingly obvious that there had been some kind of successive order to the development of life. Paleontology_sentence_172

This encouraged early evolutionary theories on the transmutation of species. Paleontology_sentence_173

After Charles Darwin published Origin of Species in 1859, much of the focus of paleontology shifted to understanding evolutionary paths, including human evolution, and evolutionary theory. Paleontology_sentence_174

The last half of the 19th century saw a tremendous expansion in paleontological activity, especially in North America. Paleontology_sentence_175

The trend continued in the 20th century with additional regions of the Earth being opened to systematic fossil collection. Paleontology_sentence_176

Fossils found in China near the end of the 20th century have been particularly important as they have provided new information about the earliest evolution of animals, early fish, dinosaurs and the evolution of birds. Paleontology_sentence_177

The last few decades of the 20th century saw a renewed interest in mass extinctions and their role in the evolution of life on Earth. Paleontology_sentence_178

There was also a renewed interest in the Cambrian explosion that apparently saw the development of the body plans of most animal phyla. Paleontology_sentence_179

The discovery of fossils of the Ediacaran biota and developments in paleobiology extended knowledge about the history of life back far before the Cambrian. Paleontology_sentence_180

Increasing awareness of Gregor Mendel's pioneering work in genetics led first to the development of population genetics and then in the mid-20th century to the modern evolutionary synthesis, which explains evolution as the outcome of events such as mutations and horizontal gene transfer, which provide genetic variation, with genetic drift and natural selection driving changes in this variation over time. Paleontology_sentence_181

Within the next few years the role and operation of DNA in genetic inheritance were discovered, leading to what is now known as the "Central Dogma" of molecular biology. Paleontology_sentence_182

In the 1960s molecular phylogenetics, the investigation of evolutionary "family trees" by techniques derived from biochemistry, began to make an impact, particularly when it was proposed that the human lineage had diverged from apes much more recently than was generally thought at the time. Paleontology_sentence_183

Although this early study compared proteins from apes and humans, most molecular phylogenetics research is now based on comparisons of RNA and DNA. Paleontology_sentence_184

See also Paleontology_section_13

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