Human evolution is the evolutionary process that led to the emergence of anatomically modern humans, beginning with the evolutionary history of primates—in particular genus Homo—and leading to the emergence of Homo sapiens as a distinct species of the hominid family, the great apes. This process involved the gradual development of traits such as human bipedalism and language, as well as interbreeding with other hominins, which indicate that human evolution was not linear but a web; the study of human evolution involves several scientific disciplines, including physical anthropology, archaeology, neurobiology, linguistics, evolutionary psychology and genetics. Genetic studies show that primates diverged from other mammals about 85 million years ago, in the Late Cretaceous period, the earliest fossils appear in the Paleocene, around 55 million years ago. Within the Hominoidea superfamily, the Hominidae family diverged from the Hylobatidae family some 15–20 million years ago. Human evolution from its first separation from the last common ancestor of humans and chimpanzees is characterized by a number of morphological, developmental and behavioral changes.
The most significant of these adaptations are bipedalism, increased brain size, lengthened ontogeny, decreased sexual dimorphism. The relationship between these changes is the subject of ongoing debate. Other significant morphological changes included the evolution of a power and precision grip, a change first occurring in H. erectus. Bipedalism is the basic adaptation of the hominid and is considered the main cause behind a suite of skeletal changes shared by all bipedal hominids; the earliest hominin, of primitive bipedalism, is considered to be either Sahelanthropus or Orrorin, both of which arose some 6 to 7 million years ago. The non-bipedal knuckle-walkers, the gorilla and chimpanzee, diverged from the hominin line over a period covering the same time, so either of Sahelanthropus or Orrorin may be our last shared ancestor. Ardipithecus, a full biped, arose 5.6 million years ago. The early bipeds evolved into the australopithecines and still into the genus Homo. There are several theories of the adaptation value of bipedalism.
It is possible that bipedalism was favored because it freed the hands for reaching and carrying food, saved energy during locomotion, enabled long distance running and hunting, provided an enhanced field of vision, helped avoid hyperthermia by reducing the surface area exposed to direct sun. A new study provides support for the hypothesis that walking on two legs, or bipedalism, evolved because it used less energy than quadrupedal knuckle-walking. However, recent studies suggest that bipedality without the ability to use fire would not have allowed global dispersal; this change in gait saw a lengthening of the legs proportionately when compared to the length of the arms, which were shortened through the removal of the need for brachiation. Another change is the shape of the big toe. Recent studies suggest that Australopithecines still lived part of the time in trees as a result of maintaining a grasping big toe; this was progressively lost in Habilines. Anatomically, the evolution of bipedalism has been accompanied by a large number of skeletal changes, not just to the legs and pelvis, but to the vertebral column and ankles, skull.
The femur evolved into a more angular position to move the center of gravity toward the geometric center of the body. The knee and ankle joints became robust to better support increased weight. To support the increased weight on each vertebra in the upright position, the human vertebral column became S-shaped and the lumbar vertebrae became shorter and wider. In the feet the big toe moved into alignment with the other toes to help in forward locomotion; the arms and forearms shortened relative to the legs making it easier to run. The foramen magnum migrated under more anterior; the most significant changes occurred in the pelvic region, where the long downward facing iliac blade was shortened and widened as a requirement for keeping the center of gravity stable while walking. A drawback is that the birth canal of bipedal apes is smaller than in knuckle-walking apes, though there has been a widening of it in comparison to that of australopithecine and modern humans, permitting the passage of newborns due to the increase in cranial size but this is limited to the upper portion, since further increase can hinder normal bipedal movement.
The shortening of the pelvis and smaller birth canal evolved as a requirement for bipedalism and had significant effects on the process of human birth, much more difficult in modern humans than in other primates. During human birth, because of the variation in size of the pelvic region, the fetal head must be in a transverse position during entry into the birth canal and rotate about 90 degrees upon exit; the smaller birth canal became a limiting factor to brain size increases in early humans and prompted a shorter gestation period leading to the relative immaturity of human
Evolution of spiders
The evolution of spiders has been going on for at least 380 million years, since the first true spiders evolved from crab-like chelicerate ancestors. More than 45,000 extant species have been described, organised taxonomically in 3,958 genera and 114 families. There may be more than 120,000 species. Fossil diversity rates make up a larger proportion than extant diversity would suggest with 1,593 arachnid species described out of 1,952 recognized chelicerates. Both extant and fossil species are described yearly by researchers in the field. Major developments in spider evolution include the development of spinnerets and silk secretion. Among the oldest known land arthropods are Trigonotarbids, members of an extinct order of spider-like arachnids. Trigonotarbids share many superficial characteristics with spiders, including a terrestrial lifestyle, respiration through book lungs, walking on eight legs, with a pair of leg-like pedipalps near the mouth and mouth parts. Arguments still remain open as to.
This had been a popular thought for quite some time, until an unpublished fossil was described with distinct microtubercles on its hind legs, akin to those used by spiders to direct and manipulate their silk. Trigonotarbids are not true spiders, most Trigonotarbid species have no living descendants today. One lineage, led to the earliest tetrapulmonates, which evolved into spiders, whip scorpions, close relatives. At one stage the oldest fossil spider was believed to be Attercopus which lived 380 million years ago during the Devonian. Attercopus was placed as the sister-taxon to all living spiders, but has now been reinterpreted as a member of a separate, extinct order Uraraneida which could produce silk, but did not have true spinnerets; the oldest true spiders date to about 300 million years ago. Most of these early segmented fossil spiders from the Coal Measures of Europe and North America belonged to the Mesothelae, or something similar, a group of primitive spiders with the spinnerets placed underneath the middle of the abdomen, rather than at the end as in modern spiders.
They were ground-dwelling predators, living in the giant clubmoss and fern forests of the mid-late Palaeozoic, where they were predators of other primitive arthropods. Silk may have been used as a protective covering for the eggs, a lining for a retreat hole, perhaps for simple ground sheet web and trapdoor construction; as plant and insect life diversified so did the spider's use of silk. Spiders with spinnerets at the end of the abdomen appeared more than 250 million years ago promoting the development of more elaborate sheet and maze webs for prey capture both on ground and foliage, as well as the development of the safety dragline; the oldest mygalomorph, was described from the Triassic of France and belongs to the modern family Hexathelidae. Megarachne servinei from the Permo-Carboniferous was once thought to be a giant mygalomorph spider and, with its body length of 1 foot and leg span of above 20 inches, the largest known spider to have lived on Earth, but subsequent examination by an expert revealed that it was a small sea scorpion.
By the Jurassic, the sophisticated aerial webs of the orb-weaver spiders had developed to take advantage of the diversifying groups of insects. A spider web preserved in amber, thought to be 110 million years old, shows evidence of a perfect "orb" web, the most famous, circular kind one thinks of when imagining spider webs. An examination of the drift of those genes thought to be used to produce the web-spinning behavior suggests that orb spinning was in an advanced state as many as 136 million years ago. One of these, the araneid Mongolarachne jurassica, from about 165 million years ago, recorded from Daohuogo, Inner Mongolia in China, is the largest known fossil spider; the 110-million-year-old amber-preserved web is the oldest to show trapped insects, containing a beetle, a mite, a wasp's leg, a fly. The ability to weave orb webs is thought to have been "lost", sometimes re-evolved or evolved separately, in different breeds of spiders since its first appearance. Spider taxonomy Insect evolution Brunetta, Leslie.
Spider silk: evolution and 400 million years of spinning, waiting and mating. New Haven: Yale University Press. ISBN 978-0-300-14922-7. Penney, D.. Dominican Amber Spiders: a comparative neontological approach to identification faunistics ecology and biogeography. Manchester: Siri Scientific Press. ISBN 978-0-9558636-0-8. Penney, D.. A.. Fossil Spiders: the evolutionary history of a mega-diverse order. Manchester: Siri Scientific Press. ISBN 978-0-9558636-5-3. Picture of spider fossil Dunlop, J. A. Penney, D. & Jekel, D.. A summary list of fossil spiders and their relatives. World Spider Catalog. Natural History Museum Bern, online at http://wsc.nmbe.ch, version 16.5
Fagus sylvatica, the European beech or common beech, is a deciduous tree belonging to the beech family Fagaceae. Fagus sylvatica is a large tree, capable of reaching heights of up to 50 m tall and 3 m trunk diameter, though more 25–35 m tall and up to 1.5 m trunk diameter. A 10-year-old sapling will stand about 4 m tall, it has a typical lifespan of 150–200 years, though sometimes up to 300 years. In cultivated forest stands trees are harvested at 80–120 years of age. 30 years are needed to attain full maturity. Like most trees, its form depends on the location: in forest areas, F. sylvatica grows to over 30 m, with branches being high up on the trunk. In open locations, it will become more massive; the leaves are alternate and entire or with a crenate margin, 5–10 cm long and 3–7 cm broad, with 6–7 veins on each side of the leaf. When crenate, there is one point at each vein tip, never any points between the veins; the buds are long and slender, 15–30 mm long and 2–3 mm thick, but thicker where the buds include flower buds.
The leaves of beech are not abscissed in the autumn and instead remain on the tree until the spring. This process is called marcescence; this occurs when trees are saplings or when plants are clipped as a hedge, but it often continues to occur on the lower branches when the tree is mature. Small quantities of seeds may be produced around 10 years of age, but not a heavy crop until the tree is at least 30 years old. F. sylvatica male flowers are borne in the small catkins. The female flowers produce beechnuts, small triangular nuts 15–20 millimetres long and 7–10 mm wide at the base. Flower and seed production is abundant in years following a hot and dry summer, though for two years in a row; the natural range extends from southern Sweden to northern Sicily, west to France, southern England, northern Portugal, central Spain, east to northwest Turkey, where it intergrades with the oriental beech, which replaces it further east. In the Balkans, it shows some hybridisation with oriental beech. In the southern part of its range around the Mediterranean, it grows only in mountain forests, at 600–1,800 m altitude.
Although regarded as native in southern England, recent evidence suggests that F. sylvatica did not arrive in England until about 4000 BC, or 2,000 years after the English Channel formed after the ice ages. The beech is classified as a native in the south of England and as a non-native in the north where it is removed from'native' woods. Localised pollen records have been recorded in the North of England from the Iron Age by Sir Harry Godwin. Changing climatic conditions may put beech populations in southern England under increased stress and while it may not be possible to maintain the current levels of beech in some sites it is thought that conditions for beech in north-west England will remain favourable or improve, it is planted in Britain. The nature of Norwegian beech populations is subject to debate. If native, they would represent the northern range of the species. However, molecular genetic analyses support the hypothesis that these populations represent intentional introduction from Denmark before and during the Viking Age.
However, the beech in Vestfold and at Seim north of Bergen in Norway is now spreading and regarded as native. Though not demanding of its soil type, the European beech has several significant requirements: a humid atmosphere and well-drained soil, it prefers moderately fertile ground, calcified or acidic, therefore it is found more on the side of a hill than at the bottom of a clayey basin. It is sensitive to spring frost. In Norway's oceanic climate planted trees grow well as far north as Trondheim. In Sweden, beech trees do not grow as far north as in Norway. A beech forest is dark and few species of plant are able to survive there, where the sun reaches the ground. Young beeches may grow poorly in full sunlight. In a clear-cut forest a European beech will germinate and die of excessive dryness. Under oaks with sparse leaf cover it will surpass them in height and, due to the beech's dense foliage, the oaks will die from lack of sunlight; the root system is shallow superficial, with large roots spreading out in all directions.
European beech forms ectomycorrhizas with a range of fungi including members of the genera Amanita, Cantharellus, Hebeloma and with the species Ramaria flavosaponaria. In the woodlands of southern Britain, beech is dominant over oak and elm south of a line from about north Suffolk across to Cardigan. Oak are the dominant forest trees north of this line. One of the most beautiful European beech forests called Sonian Forest is found in the southeast of Brussels, Belgium. Beech is a dominant tree species in France and constitutes about 10% of French fore
Introduction to evolution
Evolution is the process of change in all forms of life over generations, evolutionary biology is the study of how evolution occurs. Biological populations evolve through genetic changes that correspond to changes in the organisms' observable traits. Genetic changes include mutations, which are caused by damage or replication errors in organisms' DNA; as the genetic variation of a population drifts randomly over generations, natural selection leads traits to become more or less common based on the relative reproductive success of organisms with those traits. The age of the Earth is about 4.54 billion years. The earliest undisputed evidence of life on Earth dates at least from 3.5 billion years ago. Evolution does not attempt to explain the origin of life, but it does explain how early lifeforms evolved into the complex ecosystem that we see today. Based on the similarities between all present-day organisms, all life on Earth is assumed to have originated through common descent from a last universal ancestor from which all known species have diverged through the process of evolution.
All individuals have hereditary material in the form of genes received from their parents, which they pass on to any offspring. Among offspring there are variations of genes due to the introduction of new genes via random changes called mutations or via reshuffling of existing genes during sexual reproduction; the offspring differs from the parent in minor random ways. If those differences are helpful, the offspring is more to survive and reproduce; this means that more offspring in the next generation will have that helpful difference and individuals will not have equal chances of reproductive success. In this way, traits that result in organisms being better adapted to their living conditions become more common in descendant populations; these differences accumulate resulting in changes within the population. This process is responsible for the many diverse life forms in the world; the modern understanding of evolution began with the 1859 publication of Charles Darwin's On the Origin of Species.
In addition, Gregor Mendel's work with plants helped to explain the hereditary patterns of genetics. Fossil discoveries in paleontology, advances in population genetics and a global network of scientific research have provided further details into the mechanisms of evolution. Scientists now have a good understanding of the origin of new species and have observed the speciation process in the laboratory and in the wild. Evolution is the principal scientific theory that biologists use to understand life and is used in many disciplines, including medicine, conservation biology, forensics and other social-cultural applications; the main ideas of evolution may be summarized as follows: Life forms reproduce and therefore have a tendency to become more numerous. Factors such as predation and competition work against the survival of individuals; each offspring differs from their parent in random ways. If these differences are beneficial, the offspring is more to survive and reproduce; this makes it that more offspring in the next generation will have beneficial differences and fewer will have detrimental differences.
These differences accumulate over generations. Over time, populations can branch off into new species; these processes, collectively known as evolution, are responsible for the many diverse life forms seen in the world. In the 19th century, natural history collections and museums were popular; the European expansion and naval expeditions employed naturalists, while curators of grand museums showcased preserved and live specimens of the varieties of life. Charles Darwin was an English graduate trained in the disciplines of natural history; such natural historians would collect, catalogue and study the vast collections of specimens stored and managed by curators at these museums. Darwin served as a ship's naturalist on board HMS Beagle, assigned to a five-year research expedition around the world. During his voyage, he observed and collected an abundance of organisms, being interested in the diverse forms of life along the coasts of South America and the neighboring Galápagos Islands. Darwin gained extensive experience as he collected and studied the natural history of life forms from distant places.
Through his studies, he formulated the idea that each species had developed from ancestors with similar features. In 1838, he described; the size of a population depends on how much. For the population to remain the same size year after year, there must be an equilibrium, or balance between the population size and available resources. Since organisms produce more offspring than their environment can support, not all individuals can survive out of each generation. There must be a competitive struggle for resources; as a result, Darwin realised. Instead, survival of an organism depends on the differences of each individual organism, or "traits," that aid or hinder survival and reproduction. Well-adapted individuals are to leave more offspring than their less well-adapted competitors. Traits that hinder survival and reproduction would disappear over generations. Traits that help an organism survive and reproduce would accumulate over generations. Darwin realised that the unequal ability of individuals to survive and reproduce could cause gradual changes in the population and used the term natural selection to describe this process.
Observations of variations in animals and plants formed the basis of the theory of natural sele
Evolution of the eye
Many researchers have found the evolution of the eye attractive to study, because the eye distinctively exemplifies an analogous organ found in many animal forms. Simple light detection is found in bacteria, single-celled organisms and animals. Complex, image-forming eyes have evolved independently several times. Complex eyes appeared first within the few million years of the Cambrian explosion. Prior to the Cambrian, no evidence of eyes has survived, but diverse eyes are known from the Burgess shale of the Middle Cambrian, from the older Emu Bay Shale. Eyes are adapted to the various requirements of their owners, they vary in their visual acuity, the range of wavelengths they can detect, their sensitivity in low light, their ability to detect motion or to resolve objects, whether they can discriminate colours. In 1802, philosopher William Paley called it a miracle of "design". Charles Darwin himself wrote in his Origin of Species, that the evolution of the eye by natural selection seemed at first glance "absurd in the highest possible degree".
However, he went on that despite the difficulty in imagining it, its evolution was feasible:...if numerous gradations from a simple and imperfect eye to one complex and perfect can be shown to exist, each grade being useful to its possessor, as is the case. He suggested a stepwise evolution from "an optic nerve coated with pigment, without any other mechanism" to "a moderately high stage of perfection", gave examples of existing intermediate steps. Current research is investigating evolution. Biologist D. E. Nilsson has independently theorized about four general stages in the evolution of a vertebrate eye from a patch of photoreceptors. Nilsson and S. Pelger estimated in a classic paper that only a few hundred thousand generations are needed to evolve a complex eye in vertebrates. Another researcher, G. C. Young, has used the fossil record to infer evolutionary conclusions, based on the structure of eye orbits and openings in fossilized skulls for blood vessels and nerves to go through. All this adds to the growing amount of evidence.
The first fossils of eyes found to date are from the lower Cambrian period. The lower Cambrian had a burst of rapid evolution, called the "Cambrian explosion". One of the many hypotheses for "causes" of the Cambrian explosion is the "Light Switch" theory of Andrew Parker: It holds that the evolution of eyes started an arms race that accelerated evolution. Before the Cambrian explosion, animals may have sensed light, but did not use it for fast locomotion or navigation by vision; the rate of eye evolution is difficult to estimate, because the fossil record of the lower Cambrian, is poor. How fast a circular patch of photoreceptor cells evolve into a functional vertebrate eye has been estimated based on rates of mutation, relative advantage to the organism, natural selection. However, the time needed for each state was overestimated and the generation time was set to one year, common in small animals. With these pessimistic values, the vertebrate eye would still evolve from a patch of photoreceptor cells in less than 364,000 years.
Whether the eye evolved once or many times depends on the definition of an eye. All eyed animals share much of the genetic machinery for eye development; this suggests that the ancestor of eyed animals had some form of light-sensitive machinery – if it was not a dedicated optical organ. However photoreceptor cells may have evolved more than once from molecularly similar chemoreceptor cells. Photoreceptor cells existed long before the Cambrian explosion. Higher-level similarities – such as the use of the protein crystallin in the independently derived cephalopod and vertebrate lenses – reflect the co-option of a more fundamental protein to a new function within the eye. A shared trait common to all light-sensitive organs are opsins. Opsins belong to a family of photo-sensitive proteins and fall into nine groups, which existed in the urbilaterian, the last common ancestor of all bilaterally symmetrical animals. Additionally, the genetic toolkit for positioning eyes is shared by all animals: The PAX6 gene controls where eyes develop in animals ranging from octopuses to mice and fruit flies.
Such high-level genes are, by implication, much older than many of the structures that they control today. Eyes and other sensory organs evolved before the brain: There is no need for an information-processing organ before there is information to process; the earliest predecessors of the eye were photoreceptor proteins that sense light, found in unicellular organisms, called "eyespots". Eyespots can only sense ambient brightness: they can distinguish light from dark, sufficient for photoperiodism and daily synchronization of circadian rhythms, they are insufficient for vision, as they cannot distinguish shapes or determine the direction light is coming from. Eyespots are found in nearly all major animal groups, are common among unicellular organisms, including euglena; the euglena's eyespot, called a stigma, is located at its anterior end. It is a small splotch of red pigment. Together with th
Tetrapods are four-limbed animals constituting the superclass Tetrapoda. It includes existing and extinct amphibians and mammals. Tetrapods evolved from a group of animals known as the Tetrapodomorpha which, in turn, evolved from ancient Sarcopterygii around 390 million years ago in the middle Devonian period; the first tetrapods appeared by the late Devonian, 367.5 million years ago. The change from a body plan for breathing and navigating in water to a body plan enabling the animal to move on land is one of the most profound evolutionary changes known; the first tetrapods were aquatic. Modern amphibians, which evolved from earlier groups, are semiaquatic. However, most tetrapod species today are amniotes, most of those are terrestrial tetrapods whose branch evolved from earlier tetrapods about 340 million years ago; the key innovation in amniotes over amphibians is laying of eggs on land or having further evolved to retain the fertilized egg within the mother. Amniote tetrapods drove most amphibian tetrapods to extinction.
One group of amniotes diverged into the reptiles, which includes lepidosaurs, crocodilians and extinct relatives. Amniotes include the tetrapods that further evolved for flight—such as birds from among the dinosaurs, bats from among the mammals; some tetrapods, such as the snakes, have lost some or all of their limbs through further speciation and evolution. Others, such as amphibians, returned to or aquatic lives, the first during the Carboniferous period. Tetrapods have numerous anatomical and physiological features that are distinct from their aquatic ancestors; these include the structure of the jaw and teeth for feeding on land, limb girdles and extremities for land locomotion, lungs for respiration in air, a heart for circulation, eyes and ears for seeing and hearing in air. Tetrapods can be defined in cladistics as the nearest common ancestor of all living amphibians and all living amniotes, along with all of the descendants of that ancestor; this is a node-based definition. The group so defined is crown tetrapods.
The term tetrapodomorph is used for the stem-based definition: any animal, more related to living amphibians, reptiles and mammals than to living dipnoi. The group so defined is known as the tetrapod total group. Stegocephalia is a larger group equivalent to some broader uses of the word tetrapod, used by scientists who prefer to reserve tetrapod for the crown group; such scientists use the term "stem-tetrapod" to refer to those tetrapod-like vertebrates that are not members of the crown group, including the tetrapodomorph fishes. The two subclades of crown tetrapods are Reptiliomorpha. Batrachomorphs are all animals sharing a more recent common ancestry with living amphibians than with living amniotes. Reptiliomorphs are all animals sharing a more recent common ancestry with living amniotes than with living amphibians. Tetrapoda includes four living classes: amphibians, reptiles and birds. Overall, the biodiversity of lissamphibians, as well as of tetrapods has grown exponentially over time. However, that diversification process was interrupted at least a few times by major biological crises, such as the Permian–Triassic extinction event, which at least affected amniotes.
The overall composition of biodiversity was driven by amphibians in the Palaeozoic, dominated by reptiles in the Mesozoic and expanded by the explosive growth of birds and mammals in the Cenozoic. As biodiversity has grown, so has the number of niches that tetrapods have occupied; the first tetrapods were aquatic and fed on fish. Today, the Earth supports a great diversity of tetrapods that live in many habitats and subsist on a variety of diets; the following table shows summary estimates for each tetrapod class from the IUCN Red List of Threatened Species, 2014.3, for the number of extant species that have been described in the literature, as well as the number of threatened species. The classification of tetrapods has a long history. Traditionally, tetrapods are divided into four classes based on gross anatomical and physiological traits. Snakes and other legless reptiles are considered tetrapods because they are sufficiently like other reptiles that have a full complement of limbs. Similar considerations apply to aquatic mammals.
Newer taxonomy is based on cladistics instead, giving a variable number of major "branches" of the tetrapod family tree. As is the case throughout evolutionary biology today, there is debate over how to properly classify the groups within Tetrapoda. Traditional biological classification sometimes fa
Micropaleontology is the branch of paleontology that studies microfossils, or fossils that require the use of a microscope to see the organism, its morphology and its characteristic details. Microfossils are fossils that are between 0.001mm and 1 mm in size, the study of which requires the use of light or electron microscopy. Fossils which can be studied with the naked eye or low-powered magnification, such as a hand lens, are referred to as macrofossils. For example, some colonial organisms, such as Bryozoa have large colonies, but are classified by fine skeletal details of the small individuals of the colony. In another example, many fossil genera of Foraminifera, which are protists are known from shells that were as big as coins, such as the genus Nummulites. Microfossils are a common feature of the geological record, from the Precambrian to the Holocene, they are most common in deposits of marine environments, but occur in brackish water, fresh water and terrestrial sedimentary deposits.
While every kingdom of life is represented in the microfossil record, the most abundant forms are protist skeletons or cysts from the Chrysophyta, Sarcodina and chitinozoans, together with pollen and spores from the vascular plants. In 2017, fossilized microorganisms, or microfossils, were announced to have been discovered in hydrothermal vent precipitates in the Nuvvuagittuq Belt of Quebec, Canada that may be as old as 4.28 billion years old, the oldest record of life on Earth, suggesting "an instantaneous emergence of life", after ocean formation 4.41 billion years ago, not long after the formation of the Earth 4.54 billion years ago. Nonetheless, life may have started earlier, at nearly 4.5 billion years ago, as claimed by some researchers. Micropaleontology can be divided into four areas of study on the basis of microfossil composition: calcareous, as in coccoliths and foraminifera, phosphatic, as in the study of some vertebrates, siliceous, as in diatoms and radiolaria, or organic, as in the pollen and spores studied in palynology.
This division reflects differences in the mineralogical and chemical composition of microfossil remains rather than any strict taxonomic or ecological distinctions. Most researchers in this field, known as micropaleontologists, are specialists in one or more taxonomic groups. Calcareous microfossils include coccoliths, calcareous dinoflagellate cysts, ostracods. Phosphatic microfossils include conodonts, some scolecodonts, Shark spines and teeth, other Fish remains. Siliceous microfossils include diatoms, silicoflagellates, phytoliths, some scolecodonts, sponge spicules; the study of organic microfossils is called palynology. Organic microfossils include pollen, chitinozoans, acritarchs, dinoflagellate cysts, fungal remains. Sediment or rock samples are collected from either cores or outcrops, the microfossils they contain are extracted by a variety of physical and chemical laboratory techniques, including sieving, density separation by centrifuge or in heavy liquids, chemical digestion of the unwanted fraction.
The resulting concentrated sample of microfossils is mounted on a slide for analysis by light microscope. Taxa are identified and counted; the enormous numbers of microfossils that a small sediment sample can yield allows the collection of statistically robust datasets which can be subjected to multivariate analysis. A typical microfossil study will involve identification of a few hundred specimens from each sample. Microfossils are specially noteworthy for their importance in biostratigraphy. Since microfossils are extremely abundant and quick to appear and disappear from the stratigraphic record, they constitute ideal index fossils from a biostratigraphic perspective; the planktonic and nektonic habits of some microfossils give them the bonus of appearing across a wide range of facies or paleoenvironments, as well as having near-global distribution, making biostratigraphic correlation more powerful and effective. Microfossils from deep-sea sediments provide some of the most important records of global environmental change on long, medium or short timescales.
Across vast areas of the ocean floor, the shells of planktonic micro-organisms sinking from surface waters provide the dominant source of sediment, they continuously accumulate. Study of changes in assemblages of microfossils and changes in their shell chemistry are fundamental to research on climate change in the geological past. In addition to providing an excellent tool for sedimentary rock dating and for paleoenvironmental reconstruction – used in both petroleum geology and paleoceanography – micropaleontology has found a number of less orthodox applications, such as its growing role in forensic police investigation or in determining the provenance of archaeological artefacts. Micropaleontology is a tool of geoarchaeology used in the archaeological reconstruction of human habitation sites and environments. Changes in the microfossil population abundance in the stratigraphy of current and former water bodies reflect changes in environmental conditions. Occurring ostracods in freshwater bodies are impacted b