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Vilamitjana

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Vilamitjana is a locality and decentralized municipal entity located in the municipality of Tremp , in Province of Lleida province, Catalonia , Spain . As of 2020, it has a population of 162.

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112-557: Vilamitjana is located 95km north-northeast of Lleida. Vilamitjana is known by the finding of an important paleontological site named: Les Serretes. In this site there have found dinosaur remains that belongs to the Second biggest hadrosaur found in Spain, and the biggest of Catalonia. It was identifyied as Blasisaurus aff. Also there have been found two carnívor dinosaur tooth that belongs to two new dinosaur species morphotypes. Picture of

224-465: A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses ). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as regulatory sequences (see non-coding DNA ), and often a substantial fraction of junk DNA with no evident function. Almost all eukaryotes have mitochondria and

336-471: A jigsaw puzzle . Rocks normally form relatively horizontal layers, with each layer younger than the one underneath it. If a fossil is found between two layers whose ages are known, the fossil's age must lie between the two known ages. 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. However, fossils of species that survived for

448-408: A mouse , the plant Arabidopsis thaliana , the puffer fish , and the bacteria E. coli . In December 2013, scientists first sequenced the entire genome of a Neanderthal , an extinct species of humans . The genome was extracted from the toe bone of a 130,000-year-old Neanderthal found in a Siberian cave . New sequencing technologies, such as massive parallel sequencing have also opened up

560-430: A big potential to modify the genetic control in a host organism. The movement of TEs is a driving force of genome evolution in eukaryotes because their insertion can disrupt gene functions, homologous recombination between TEs can produce duplications, and TE can shuffle exons and regulatory sequences to new locations. Retrotransposons are found mostly in eukaryotes but not found in prokaryotes. Retrotransposons form

672-544: A collision that formed the Moon about 40 million years later, may have cooled quickly enough to have oceans and an atmosphere about 4,440  million years ago . There is evidence on the Moon of a Late Heavy Bombardment by asteroids from 4,000 to 3,800 million years ago . If, as seems likely, such a bombardment struck Earth at the same time, the first atmosphere and oceans may have been stripped away. Paleontology traces

784-602: A common ancestor. 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. 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. Evolutionary developmental biology , commonly abbreviated to "Evo Devo", also helps paleontologists to produce "family trees", and understand fossils. For example,

896-451: A constant rate. 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. Earth formed about 4,570  million years ago and, after

1008-403: A data source that is not limited to animals with easily fossilised hard parts, and they reflect organisms' behaviours. Also many traces date from significantly earlier than the body fossils of animals that are thought to have been capable of making them. Whilst exact assignment of trace fossils to their makers is generally impossible, traces may for example provide the earliest physical evidence of

1120-506: A defined structure that are able to change their location in the genome. TEs are categorized as either as a mechanism that replicates by copy-and-paste or as a mechanism that can be excised from the genome and inserted at a new location. In the human genome, there are three important classes of TEs that make up more than 45% of the human DNA; these classes are The long interspersed nuclear elements (LINEs), The interspersed nuclear elements (SINEs), and endogenous retroviruses. These elements have

1232-567: A fortunate accident during other research. For example, the 1980 discovery by Luis and Walter Alvarez of iridium , a mainly extraterrestrial metal, in the Cretaceous – Paleogene boundary layer made asteroid impact the most favored explanation for the Cretaceous–Paleogene extinction event – although debate continues about the contribution of volcanism. A complementary approach to developing scientific knowledge, experimental science ,

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1344-609: A genome sequence and aids in navigating around the genome. The Human Genome Project was organized to map and to sequence the human genome . A fundamental step in the project was the release of a detailed genomic map by Jean Weissenbach and his team at the Genoscope in Paris. Reference genome sequences and maps continue to be updated, removing errors and clarifying regions of high allelic complexity. The decreasing cost of genomic mapping has permitted genealogical sites to offer it as

1456-531: A large portion of the genomes of many eukaryotes. A retrotransposon is a transposable element that transposes through an RNA intermediate. Retrotransposons are composed of DNA , but are transcribed into RNA for transposition, then the RNA transcript is copied back to DNA formation with the help of a specific enzyme called reverse transcriptase. A retrotransposon that carries reverse transcriptase in its sequence can trigger its own transposition but retrotransposons that lack

1568-405: A main driving role to generate genetic novelty and natural genome editing. Works of science fiction illustrate concerns about the availability of genome sequences. Michael Crichton's 1990 novel Jurassic Park and the subsequent film tell the story of a billionaire who creates a theme park of cloned dinosaurs on a remote island, with disastrous outcomes. A geneticist extracts dinosaur DNA from

1680-413: A major role in shaping the genome. Duplication may range from extension of short tandem repeats , to duplication of a cluster of genes, and all the way to duplication of entire chromosomes or even entire genomes . Such duplications are probably fundamental to the creation of genetic novelty. Horizontal gene transfer is invoked to explain how there is often an extreme similarity between small portions of

1792-467: A major theme of the book. The 1997 film Gattaca is set in a futurist society where genomes of children are engineered to contain the most ideal combination of their parents' traits, and metrics such as risk of heart disease and predicted life expectancy are documented for each person based on their genome. People conceived outside of the eugenics program, known as "In-Valids" suffer discrimination and are relegated to menial occupations. The protagonist of

1904-814: A minor group until the first jawed fish appeared in the Late Ordovician . 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 . The earliest evidence of land plants and land invertebrates date back to about 476  million years ago and 490  million years ago respectively. Those invertebrates, as indicated by their trace and body fossils, were shown to be arthropods known as euthycarcinoids . The lineage that produced land vertebrates evolved later but very rapidly between 370  million years ago and 360  million years ago ; recent discoveries have overturned earlier ideas about

2016-474: A new site. This cut-and-paste mechanism typically reinserts transposons near their original location (within 100 kb). DNA transposons are found in bacteria and make up 3% of the human genome and 12% of the genome of the roundworm C. elegans . Genome size is the total number of the DNA base pairs in one copy of a haploid genome. Genome size varies widely across species. Invertebrates have small genomes, this

2128-501: A precise definition of "genome." It usually refers to the DNA (or sometimes RNA) molecules that carry the genetic information in an organism but sometimes it is difficult to decide which molecules to include in the definition; for example, bacteria usually have one or two large DNA molecules ( chromosomes ) that contain all of the essential genetic material but they also contain smaller extrachromosomal plasmid molecules that carry important genetic information. The definition of 'genome' that

2240-555: 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. Although she was rarely recognised by the scientific community, Mary Anning was a significant contributor to the field of palaeontology during this period; she uncovered multiple novel Mesozoic reptile fossils and deducted that what were then known as bezoar stones are in fact fossilised faeces . In 1822 Henri Marie Ducrotay de Blainville , editor of Journal de Physique , coined

2352-415: A reference, whereas analyses of coverage depth and mapping topology can provide details regarding structural variations such as chromosomal translocations and segmental duplications. DNA sequences that carry the instructions to make proteins are referred to as coding sequences. The proportion of the genome occupied by coding sequences varies widely. A larger genome does not necessarily contain more genes, and

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2464-535: A relatively short time can be used to link up isolated rocks: this technique is called biostratigraphy . For instance, the conodont Eoplacognathus pseudoplanus has a short range in the Middle Ordovician period. If rocks of unknown age are found to have traces of E. pseudoplanus , they must have a mid-Ordovician age. Such index fossils must be distinctive, be globally distributed and have a short time range to be useful. However, misleading results are produced if

2576-487: A reverse transcriptase must use reverse transcriptase synthesized by another retrotransposon. Retrotransposons can be transcribed into RNA, which are then duplicated at another site into the genome. Retrotransposons can be divided into long terminal repeats (LTRs) and non-long terminal repeats (Non-LTRs). Long terminal repeats (LTRs) are derived from ancient retroviral infections, so they encode proteins related to retroviral proteins including gag (structural proteins of

2688-641: A service, to the extent that one may submit one's genome to crowdsourced scientific endeavours such as DNA.LAND at the New York Genome Center , an example both of the economies of scale and of citizen science . Viral genomes can be composed of either RNA or DNA. The genomes of RNA viruses can be either single-stranded RNA or double-stranded RNA , and may contain one or more separate RNA molecules (segments: monopartit or multipartit genome). DNA viruses can have either single-stranded or double-stranded genomes. Most DNA virus genomes are composed of

2800-404: A single, linear molecule of DNA, but some are made up of a circular DNA molecule. Prokaryotes and eukaryotes have DNA genomes. Archaea and most bacteria have a single circular chromosome , however, some bacterial species have linear or multiple chromosomes. If the DNA is replicated faster than the bacterial cells divide, multiple copies of the chromosome can be present in a single cell, and if

2912-509: A small mitochondrial genome . Algae and plants also contain chloroplasts with a chloroplast genome. The study of the genome is called genomics . The genomes of many organisms have been sequenced and various regions have been annotated. The Human Genome Project was started in October 1990, and then reported the sequence of the human genome in April 2003, although the initial "finished" sequence

3024-554: A species. Within a species, the vast majority of nucleotides are identical between individuals, but sequencing multiple individuals is necessary to understand the genetic diversity. In 1976, Walter Fiers at the University of Ghent (Belgium) was the first to establish the complete nucleotide sequence of a viral RNA-genome ( Bacteriophage MS2 ). The next year, Fred Sanger completed the first DNA-genome sequence: Phage Φ-X174 , of 5386 base pairs. The first bacterial genome to be sequenced

3136-604: A steady increase in brain size after about 3  million years ago . 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 . Life on earth has suffered occasional mass extinctions at least since 542  million years ago . Despite their disastrous effects, mass extinctions have sometimes accelerated

3248-485: Is also correlated to a small number of transposable elements. Fish and Amphibians have intermediate-size genomes, and birds have relatively small genomes but it has been suggested that birds lost a substantial portion of their genomes during the phase of transition to flight.  Before this loss, DNA methylation allows the adequate expansion of the genome. In humans, the nuclear genome comprises approximately 3.1 billion nucleotides of DNA, divided into 24 linear molecules,

3360-432: Is another DIRS-like elements belong to Non-LTRs. Non-LTRs are widely spread in eukaryotic genomes. Long interspersed elements (LINEs) encode genes for reverse transcriptase and endonuclease, making them autonomous transposable elements. The human genome has around 500,000 LINEs, taking around 17% of the genome. Short interspersed elements (SINEs) are usually less than 500 base pairs and are non-autonomous, so they rely on

3472-444: Is carried in plasmids . For this, the word genome should not be used as a synonym of chromosome . Eukaryotic genomes are composed of one or more linear DNA chromosomes. The number of chromosomes varies widely from Jack jumper ants and an asexual nemotode , which each have only one pair, to a fern species that has 720 pairs. It is surprising the amount of DNA that eukaryotic genomes contain compared to other genomes. The amount

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3584-408: Is commonly used in the scientific literature is usually restricted to the large chromosomal DNA molecules in bacteria. Eukaryotic genomes are even more difficult to define because almost all eukaryotic species contain nuclear chromosomes plus extra DNA molecules in the mitochondria . In addition, algae and plants have chloroplast DNA. Most textbooks make a distinction between the nuclear genome and

3696-584: Is composed only of eukaryotic cells, and the earliest evidence for it is the Francevillian Group Fossils from 2,100  million years ago , although specialisation of cells for different functions first appears between 1,430  million years ago (a possible fungus) and 1,200  million years ago (a probable red alga ). 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

3808-564: Is even more than what is necessary for DNA protein-coding and noncoding genes due to the fact that eukaryotic genomes show as much as 64,000-fold variation in their sizes. However, this special characteristic is caused by the presence of repetitive DNA, and transposable elements (TEs). A typical human cell has two copies of each of 22 autosomes , one inherited from each parent, plus two sex chromosomes , making it diploid. Gametes , such as ova, sperm, spores, and pollen, are haploid, meaning they carry only one copy of each chromosome. In addition to

3920-492: Is facilitated by active DNA demethylation , a process that entails the DNA base excision repair pathway. This pathway is employed in the erasure of CpG methylation (5mC) in primordial germ cells. The erasure of 5mC occurs via its conversion to 5-hydroxymethylcytosine (5hmC) driven by high levels of the ten-eleven dioxygenase enzymes TET1 and TET2 . Genomes are more than the sum of an organism's genes and have traits that may be measured and studied without reference to

4032-477: 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. Paleontologists generally use approaches based on cladistics , a technique for working out the evolutionary "family tree" of a set of organisms. It works by

4144-443: Is often said to work by conducting experiments to disprove hypotheses about the workings and causes of natural phenomena. 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. However, when confronted with totally unexpected phenomena, such as the first evidence for invisible radiation , experimental scientists often use

4256-594: Is one that contained an extinct "crocodile-like" marine reptile, which eventually came to be known as the mosasaurid Mosasaurus of the Cretaceous period. 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. Interest increased for reasons that were not purely scientific, as geology and paleontology helped industrialists to find and exploit natural resources such as coal. This contributed to

4368-401: 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. 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

4480-401: Is rather exceptional, eukaryotes generally have these features in their genes and their genomes contain variable amounts of repetitive DNA. In mammals and plants, the majority of the genome is composed of repetitive DNA. High-throughput technology makes sequencing to assemble new genomes accessible to everyone. Sequence polymorphisms are typically discovered by comparing resequenced isolates to

4592-451: Is the scientific study of life that existed prior to the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossils to classify organisms and study their interactions with each other and their environments (their paleoecology ). Paleontological observations have been documented as far back as the 5th century BC. The science became established in

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4704-503: Is thought to have been propelled by coevolution with pollinating insects. 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. Humans evolved from a lineage of upright-walking apes whose earliest fossils date from over 6  million years ago . Although early members of this lineage had chimp -sized brains, about 25% as big as modern humans', there are signs of

4816-421: Is to reduce the number of genes in a genome to the bare minimum and still have the organism in question survive. There is experimental work being done on minimal genomes for single cell organisms as well as minimal genomes for multi-cellular organisms (see developmental biology ). The work is both in vivo and in silico . There are many enormous differences in size in genomes, specially mentioned before in

4928-567: 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. 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. In early modern Europe ,

5040-528: The Neogene - Quaternary . In deeper-level deposits in western Europe are early-aged mammals such as the palaeothere perissodactyl Palaeotherium and the anoplotheriid artiodactyl Anoplotherium , both of which were described earliest after the former two genera, which today are known to date to the Paleogene period. Cuvier figured out that even older than the two levels of deposits with extinct large mammals

5152-637: The Permian–Triassic extinction event . Amphibians Extinct Synapsids Mammals Extinct reptiles Lizards and snakes Extinct Archosaurs Crocodilians Extinct Dinosaurs Birds 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. 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. For example: it

5264-513: The Permian–Triassic extinction event . A relatively recent discipline, molecular phylogenetics , compares the DNA and RNA of modern organisms to re-construct the "family trees" of their evolutionary ancestors. 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 ". Techniques from engineering have been used to analyse how

5376-487: The University of Hamburg , Germany. The website Oxford Dictionaries and the Online Etymology Dictionary suggest the name is a blend of the words gene and chromosome . However, see omics for a more thorough discussion. A few related -ome words already existed, such as biome and rhizome , forming a vocabulary into which genome fits systematically. It is very difficult to come up with

5488-454: The embryological development of some modern brachiopods suggests that brachiopods may be descendants of the halkieriids , which became extinct in the Cambrian period. Paleontology seeks to map out how living things have changed through time. A substantial hurdle to this aim is the difficulty of working out how old fossils are. Beds that preserve fossils typically lack the radioactive elements needed for radiometric dating . This technique

5600-521: The " jigsaw puzzles " of biostratigraphy (arrangement of rock layers from youngest to oldest). 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". The final quarter of the 20th century saw the development of molecular phylogenetics , which investigates how closely organisms are related by measuring

5712-463: The 18th century as a result of Georges Cuvier 's work on comparative anatomy , and developed rapidly in the 19th century. The term has been used since 1822 formed from Greek παλαιός ( 'palaios' , "old, ancient"), ὄν ( 'on' , ( gen. 'ontos' ), "being, creature"), and λόγος ( 'logos' , "speech, thought, study"). Paleontology lies on the border between biology and geology , but it differs from archaeology in that it excludes

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5824-548: The Early Cambrian , along with several "weird wonders" that bear little obvious resemblance to any modern animals. 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. Vertebrates remained

5936-459: The Earth's organic and inorganic past". 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. Hence it has three main elements: description of past phenomena; developing a general theory about

6048-426: The X and Y chromosomes of mammals, so the technical definition of the genome must include both copies of the sex chromosomes. For example, the standard reference genome of humans consists of one copy of each of the 22 autosomes plus one X chromosome and one Y chromosome. A genome sequence is the complete list of the nucleotides (A, C, G, and T for DNA genomes) that make up all the chromosomes of an individual or

6160-412: The ability to reproduce. The earliest known animals are cnidarians from about 580  million years ago , but these are so modern-looking that they must be descendants of earlier animals. Early fossils of animals are rare because they had not developed mineralised , easily fossilized hard parts until about 548  million years ago . The earliest modern-looking bilaterian animals appear in

6272-515: The appearance of moderately complex animals (comparable to earthworms ). Geochemical observations may help to deduce the global level of biological activity at a certain period, or the affinity of certain fossils. 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. Analyses of carbon isotope ratios may help to explain major transitions such as

6384-625: The atmosphere increased their effectiveness as nurseries of evolution. 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. This innovation may have come from primitive eukaryotes capturing oxygen-powered bacteria as endosymbionts and transforming them into organelles called mitochondria . The earliest evidence of complex eukaryotes with organelles (such as mitochondria) dates from 1,850  million years ago . Multicellular life

6496-412: The blood of ancient mosquitoes and fills in the gaps with DNA from modern species to create several species of dinosaurs. A chaos theorist is asked to give his expert opinion on the safety of engineering an ecosystem with the dinosaurs, and he repeatedly warns that the outcomes of the project will be unpredictable and ultimately uncontrollable. These warnings about the perils of using genomic information are

6608-415: The bodies of ancient organisms might have worked, for example the running speed and bite strength of Tyrannosaurus , or the flight mechanics of Microraptor . It is relatively commonplace to study the internal details of fossils using X-ray microtomography . Paleontology, biology, archaeology, and paleoneurobiology combine to study endocranial casts (endocasts) of species related to humans to clarify

6720-401: The causes of various types of change; and applying those theories to specific facts. 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. Sometimes researchers discover a "smoking gun" by

6832-549: The cells divide faster than the DNA can be replicated, multiple replication of the chromosome is initiated before the division occurs, allowing daughter cells to inherit complete genomes and already partially replicated chromosomes. Most prokaryotes have very little repetitive DNA in their genomes. However, some symbiotic bacteria (e.g. Serratia symbiotica ) have reduced genomes and a high fraction of pseudogenes: only ~40% of their DNA encodes proteins. Some bacteria have auxiliary genetic material, also part of their genome, which

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6944-763: The characteristics and evolution of humans as a species. 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 the people who lived there, and what they ate; or they might analyze the climate at the time of habitation. In addition, paleontology often borrows techniques from other sciences, including biology, osteology , ecology, chemistry , physics and mathematics. 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

7056-478: The chromosomes in the nucleus, organelles such as the chloroplasts and mitochondria have their own DNA. Mitochondria are sometimes said to have their own genome often referred to as the " mitochondrial genome ". The DNA found within the chloroplast may be referred to as the " plastome ". Like the bacteria they originated from, mitochondria and chloroplasts have a circular chromosome. Unlike prokaryotes where exon-intron organization of protein coding genes exists but

7168-520: The chronological order in which rocks were formed, is useful to both paleontologists and geologists. Biogeography studies the spatial distribution of organisms, and is also linked to geology, which explains how Earth's geography has changed over time. Although paleontology became established around 1800, earlier thinkers had noticed aspects of the fossil record. The ancient Greek philosopher Xenophanes (570–480 BCE) concluded from fossil sea shells that some areas of land were once under water. During

7280-445: The date when 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 ancestor must have lived – by assuming that DNA mutations accumulate at

7392-451: The dentary from les Serretes. Nowadays exposed on the Museum of Isona . This Province of Lleida location article is a stub . You can help Misplaced Pages by expanding it . Paleontology Paleontology ( / ˌ p eɪ l i ɒ n ˈ t ɒ l ə dʒ i , ˌ p æ l i -, - ən -/ PAY -lee-on- TOL -ə-jee, PAL -ee-, -⁠ən- ), also spelled palaeontology or palæontology ,

7504-445: The details of any particular genes and their products. Researchers compare traits such as karyotype (chromosome number), genome size , gene order, codon usage bias , and GC-content to determine what mechanisms could have produced the great variety of genomes that exist today (for recent overviews, see Brown 2002; Saccone and Pesole 2003; Benfey and Protopapas 2004; Gibson and Muse 2004; Reese 2004; Gregory 2005). Duplications play

7616-586: The development of mammalian traits such as endothermy and hair. After the Cretaceous–Paleogene extinction event 66  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. Fossil evidence indicates that flowering plants appeared and rapidly diversified in the Early Cretaceous between 130  million years ago and 90  million years ago . Their rapid rise to dominance of terrestrial ecosystems

7728-551: The development of the body plans of most animal phyla . The discovery of fossils of the Ediacaran biota and developments in paleobiology extended knowledge about the history of life back far before the Cambrian. 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

7840-477: The different levels of deposits represented different time periods in the early 19th century. The surface-level deposits in the Americas contained later mammals like the megatheriid ground sloth Megatherium and the mammutid proboscidean Mammut (later known informally as a "mastodon"), which were some of the earliest-named fossil mammal genera with official taxonomic authorities. They today are known to date to

7952-409: 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. 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. There was also a renewed interest in the Cambrian explosion that apparently saw

8064-407: The evolution of life on earth. 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 a new group, which may possess an advantageous trait, to outlive the old and move into its niche. Genome In the fields of molecular biology and genetics ,

8176-410: The evolution of the human brain. 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. As knowledge has increased, paleontology has developed specialised subdivisions. Vertebrate paleontology concentrates on fossils from the earliest fish to

8288-466: The evolutionary history of life back to over 3,000  million years ago , possibly as far as 3,800  million years ago . The oldest clear evidence of life on Earth dates to 3,000  million years ago , although there have been reports, often disputed, of fossil bacteria from 3,400  million years ago and of geochemical evidence for the presence of life 3,800  million years ago . Some scientists have proposed that life on Earth

8400-555: The exceptional events that cause quick burial make it difficult to study the normal environments of the animals. 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 . Trace fossils consist mainly of tracks and burrows, but also include coprolites (fossil feces ) and marks left by feeding. Trace fossils are particularly significant because they represent

8512-504: The focus of paleontology shifted to understanding evolutionary paths, including human evolution , and evolutionary theory. The last half of the 19th century saw a tremendous expansion in paleontological activity, especially in North America. The trend continued in the 20th century with additional regions of the Earth being opened to systematic fossil collection. Fossils found in China near

8624-449: The following: 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. The expanding knowledge of the fossil record also played an increasing role in the development of geology, particularly stratigraphy . Cuvier proved that

8736-580: The fossil record: different environments are more favorable to the preservation of different types of organism or parts of organisms. 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. Occasionally, unusual environments may preserve soft tissues. These lagerstätten allow paleontologists to examine

8848-406: The genomes of two organisms that are otherwise very distantly related. Horizontal gene transfer seems to be common among many microbes . Also, eukaryotic cells seem to have experienced a transfer of some genetic material from their chloroplast and mitochondrial genomes to their nuclear chromosomes. Recent empirical data suggest an important role of viruses and sub-viral RNA-networks to represent

8960-675: The history and driving forces behind their evolution. 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. During the Permian period, synapsids , including the ancestors of mammals , may have dominated land environments, but this ended with the Permian–Triassic extinction event 251  million years ago , which came very close to wiping out all complex life. The extinctions were apparently fairly sudden, at least among vertebrates. During

9072-521: 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. Biostratigraphy , the use of fossils to work out

9184-455: The human genome All the cells of an organism originate from a single cell, so they are expected to have identical genomes; however, in some cases, differences arise. Both the process of copying DNA during cell division and exposure to environmental mutagens can result in mutations in somatic cells. In some cases, such mutations lead to cancer because they cause cells to divide more quickly and invade surrounding tissues. In certain lymphocytes in

9296-425: The human genome and 9% of the fruit fly genome. Tandem repeats can be functional. For example, telomeres are composed of the tandem repeat TTAGGG in mammals, and they play an important role in protecting the ends of the chromosome. In other cases, expansions in the number of tandem repeats in exons or introns can cause disease . For example, the human gene huntingtin (Htt) typically contains 6–29 tandem repeats of

9408-517: The human immune system, V(D)J recombination generates different genomic sequences such that each cell produces a unique antibody or T cell receptors. During meiosis , diploid cells divide twice to produce haploid germ cells. During this process, recombination results in a reshuffling of the genetic material from homologous chromosomes so each gamete has a unique genome. Genome-wide reprogramming in mouse primordial germ cells involves epigenetic imprint erasure leading to totipotency . Reprogramming

9520-542: The immediate ancestors of modern mammals . Invertebrate paleontology deals with fossils such as molluscs , arthropods , annelid worms and echinoderms . Paleobotany studies fossil plants , algae , and fungi. 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. Micropaleontology deals with microscopic fossil organisms of all kinds. Instead of focusing on individual organisms, paleoecology examines

9632-434: The index fossils turn out to have longer fossil ranges than first thought. Stratigraphy and biostratigraphy can in general provide only relative dating ( A was before B ), which is often sufficient for studying evolution. However, this is difficult for some time periods, because of the problems involved in matching up rocks of the same age across different continents . Family-tree relationships may also help to narrow down

9744-538: The interactions between different ancient organisms, such as their food chains , and the two-way interactions with their environments.   For example, the development of oxygenic photosynthesis by bacteria caused the oxygenation of the atmosphere and hugely increased the productivity and diversity of ecosystems . Together, these led to the evolution of complex eukaryotic cells, from which all multicellular organisms are built. Paleoclimatology , although sometimes treated as part of paleoecology, focuses more on

9856-463: The internal anatomy of animals that in other sediments are represented only by shells, spines, claws, etc. – if they are preserved at all. However, even lagerstätten present an incomplete picture of life at the time. 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

9968-456: 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. Although this early study compared proteins from apes and humans, most molecular phylogenetics research is now based on comparisons of RNA and DNA . Fossils of organisms' bodies are usually

10080-409: 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 that are compared may be anatomical , such as the presence of a notochord , or molecular , by comparing sequences of DNA or proteins . The result of a successful analysis is a hierarchy of clades – groups that share

10192-409: The most informative type of evidence. The most common types are wood, bones, and shells. 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, it is often adequate to illustrate the broader patterns of life's history. There are also biases in

10304-476: The multicellular eukaryotic genomes. Much of this is due to the differing abundances of transposable elements, which evolve by creating new copies of themselves in the chromosomes. Eukaryote genomes often contain many thousands of copies of these elements, most of which have acquired mutations that make them defective. Here is a table of some significant or representative genomes. See #See also for lists of sequenced genomes. Initial sequencing and analysis of

10416-789: The nucleotides CAG (encoding a polyglutamine tract). An expansion to over 36 repeats results in Huntington's disease , a neurodegenerative disease. Twenty human disorders are known to result from similar tandem repeat expansions in various genes. The mechanism by which proteins with expanded polygulatamine tracts cause death of neurons is not fully understood. One possibility is that the proteins fail to fold properly and avoid degradation, instead accumulating in aggregates that also sequester important transcription factors, thereby altering gene expression. Tandem repeats are usually caused by slippage during replication, unequal crossing-over and gene conversion. Transposable elements (TEs) are sequences of DNA with

10528-447: The organelle (mitochondria and chloroplast) genomes so when they speak of, say, the human genome, they are only referring to the genetic material in the nucleus. This is the most common use of 'genome' in the scientific literature. Most eukaryotes are diploid , meaning that there are two of each chromosome in the nucleus but the 'genome' refers to only one copy of each chromosome. Some eukaryotes have distinctive sex chromosomes, such as

10640-414: 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. 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 . In the 1960s molecular phylogenetics ,

10752-452: 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. 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

10864-590: The proportion of non-repetitive DNA decreases along with increasing genome size in complex eukaryotes. Noncoding sequences include introns , sequences for non-coding RNAs, regulatory regions, and repetitive DNA. Noncoding sequences make up 98% of the human genome. There are two categories of repetitive DNA in the genome: tandem repeats and interspersed repeats. Short, non-coding sequences that are repeated head-to-tail are called tandem repeats . Microsatellites consisting of 2–5 basepair repeats, while minisatellite repeats are 30–35 bp. Tandem repeats make up about 4% of

10976-412: The prospect of personal genome sequencing as a diagnostic tool, as pioneered by Manteia Predictive Medicine . A major step toward that goal was the completion in 2007 of the full genome of James D. Watson , one of the co-discoverers of the structure of DNA. Whereas a genome sequence lists the order of every DNA base in a genome, a genome map identifies the landmarks. A genome map is less detailed than

11088-439: The proteins encoded by LINEs for transposition. The Alu element is the most common SINE found in primates. It is about 350 base pairs and occupies about 11% of the human genome with around 1,500,000 copies. DNA transposons encode a transposase enzyme between inverted terminal repeats. When expressed, the transposase recognizes the terminal inverted repeats that flank the transposon and catalyzes its excision and reinsertion in

11200-432: The radioactive element was incorporated into the rock. 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. Consequently, paleontologists must usually rely on stratigraphy to date fossils. Stratigraphy is the science of deciphering the "layer-cake" that is the sedimentary record, and has been compared to

11312-701: The same approach as historical scientists: construct a set of hypotheses about the causes and then look for a "smoking gun". 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. 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 also has some overlap with archaeology , which primarily works with objects made by humans and with human remains, while paleontologists are interested in

11424-423: The shortest 45 000 000 nucleotides in length and the longest 248 000 000 nucleotides, each contained in a different chromosome. There is no clear and consistent correlation between morphological complexity and genome size in either prokaryotes or lower eukaryotes . Genome size is largely a function of the expansion and contraction of repetitive DNA elements. Since genomes are very complex, one research strategy

11536-478: The similarity of the DNA in 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. The simplest definition of "paleontology" is "the study of ancient life". 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

11648-465: The slow recovery from this catastrophe a previously obscure group, archosaurs , became the most abundant and diverse terrestrial vertebrates. One archosaur group, the dinosaurs, were the dominant land vertebrates for the rest of the Mesozoic , and birds evolved from one group of dinosaurs. During this time mammals' ancestors survived only as small, mainly nocturnal insectivores , which may have accelerated

11760-631: The study of anatomically modern humans . It now uses techniques drawn from a wide range of sciences, including biochemistry , mathematics , and engineering. Use of all these techniques has enabled paleontologists to discover much of the evolutionary history of life , almost back to when Earth became capable of supporting life, nearly 4 billion years ago. 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 . Body fossils and trace fossils are

11872-617: The systematic study of fossils emerged as an integral part of the changes in natural philosophy that occurred during the Age of Reason . In the Italian Renaissance, Leonardo da Vinci made various significant contributions to the field as well as depicted numerous fossils. 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. He identified

11984-541: The virus), pol (reverse transcriptase and integrase), pro (protease), and in some cases env (envelope) genes. These genes are flanked by long repeats at both 5' and 3' ends. It has been reported that LTRs consist of the largest fraction in most plant genome and might account for the huge variation in genome size. Non-long terminal repeats (Non-LTRs) are classified as long interspersed nuclear elements (LINEs), short interspersed nuclear elements (SINEs), and Penelope-like elements (PLEs). In Dictyostelium discoideum , there

12096-406: The word "palaeontology" to refer to the study of ancient living organisms through fossils. 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. This encouraged early evolutionary theories on the transmutation of species . After Charles Darwin published Origin of Species in 1859, much of

12208-454: Was "seeded" from elsewhere , but most research concentrates on various explanations of how life could have arisen independently on Earth. For about 2,000 million years microbial mats , multi-layered colonies of different bacteria, were the dominant life on Earth. The evolution of oxygenic photosynthesis enabled them to play the major role in the oxygenation of the atmosphere from about 2,400  million years ago . This change in

12320-429: Was completed in 1996, again by The Institute for Genomic Research. The development of new technologies has made genome sequencing dramatically cheaper and easier, and the number of complete genome sequences is growing rapidly. The US National Institutes of Health maintains one of several comprehensive databases of genomic information. Among the thousands of completed genome sequencing projects include those for rice ,

12432-473: Was missing 8% of the genome consisting mostly of repetitive sequences. With advancements in technology that could handle sequencing of the many repetitive sequences found in human DNA that were not fully uncovered by the original Human Genome Project study, scientists reported the first end-to-end human genome sequence in March 2022. The term genome was created in 1920 by Hans Winkler , professor of botany at

12544-400: Was that of Haemophilus influenzae , completed by a team at The Institute for Genomic Research in 1995. A few months later, the first eukaryotic genome was completed, with sequences of the 16 chromosomes of budding yeast Saccharomyces cerevisiae published as the result of a European-led effort begun in the mid-1980s. The first genome sequence for an archaeon , Methanococcus jannaschii ,

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