Are amphibians monocondylic

Evolution of insects - Evolution of insects

Development of insects from an ancestral crustacean and their subsequent irradiation
Evolution has produced an amazing variety of insects. Some of the possible shapes of antennas are shown.

The most recent understanding of the Evolution of insects is based on studies in the following branches of science: molecular biology, insect morphology, paleontology, insect taxonomy, evolution, embryology, bioinformatics and scientific computing. It is estimated that the class of insects originated in the Ordovician on Earth about 480 million years ago, and terrestrial plants appeared around the same time. Insects can have evolved from a group of crustaceans. The first insects were land-bound, but about 400 million years ago in the Devonian period, a line of insects developed flight, the first animals to do so. It has been suggested that the oldest insect fossil Rhyniognatha hirsti is which is estimated to be 400 million years old, but the fossil's insect identity has been contested. The global climatic conditions have changed several times in the course of the earth's history and with them the diversity of insects. The pterygotes (winged insects) were exposed to strong radiation in the Carboniferous (356 to 299 million years ago), while the endopterygota (insects that metamorphosed through various stages of life) were exposed to further strong radiation in the Permian (299 to 252 million years ago) were. .

Most of the received orders from insects developed during the Permian period. Many of the early groups died out about 252 million years ago during the mass extinction on the Permo-Triassic border, the largest extinction in Earth's history. The survivors of this event evolved in the Triassic (252 to 201 million years ago) into the essentially modern insect orders that still exist today. Most modern insect families appeared in the Jurassic (201 to 145 million years ago).

In an important example of coevolution, a number of very successful groups of insects developed - notably the Hymenoptera (wasps, bees, and ants) and Lepidoptera (butterflies), as well as many species of Diptera (flies) and Coleoptera (beetles) - associated with flowering plants during the Cretaceous Period (145 to 66 million years ago).

Many modern genera of insects developed during the Cenozoic, which began about 66 million years ago; Insects from this period were often preserved in amber, often in perfect condition. Such specimens are easy to compare with modern species, and most of them belong to the existing genera.

Fossils

conservation

Fossil mosquito in amber showing the remarkable preservation of many insect fossils.

Because of their external skeleton, insect fossil history does not depend entirely on the preservation of deposit-type, as is the case with many soft-bodied organisms. However, insects have not left behind a particularly robust fossil record due to their small size and small build. Apart from insects preserved in amber, most of the finds are terrestrial or near terrestrial sources and are only preserved under very special conditions, such as on the edge of freshwater lakes. While about 1/3 of the known non-insect species are extinct fossils, due to the lack of fossil stocks only 1/100 of the known insects are extinct fossils.

Insect fossils are often three-dimensional preservations of the original fossil. Loose wings are a common type of fossil because the wings do not decay or digest easily and are often left behind by predators. Fossilization often retains its external appearance, in contrast to vertebrate fossils, which are mostly only preserved as bony remains (or inorganic casts of them). Vertebrate fossils with similarly preserved external appearance are rare because of their size, and most of the known cases are sub-fossils. Insect fossils, when preserved, are often preserved as three-dimensional, permineralized, and charred replicas; and as inclusions in amber and even in some minerals. Sometimes even their color and pattern are still recognizable. However, conservation in amber is limited by the large amount of resin produced by trees, which only developed in the Mesozoic era.

There is also ample fossil evidence of extinct insect behavior, including feeding damage to fossil vegetation, as well as wood, fecal pellets, and nests in fossil soils. Such conservation is rare in vertebrates and is mostly limited to footprints and coprolites.

Freshwater and marine insect fossils

The common denominator among most fossil insect and land plant deposits is the marine environment. The insects that were preserved either lived in the fossil lake (autochthonous) or were carried into the lake from the surrounding habitats by winds, currents or their own flight (allochthonous). Drowning and dying insects, which are not eaten by fish and other predators, settle on the bottom where, under suitable conditions, they can be stored in the lake's sediments called lacustrine. Even amber or fossil resin from trees requires a watery environment that is lacustrine or brackish to sustain. Without protection in anoxic sediments, amber would gradually disintegrate; it is never found buried in fossil soils. Various factors play a major role in what types of insects are preserved and how well, if at all, including sea depth, temperature, and alkalinity; Type of sediment; whether the lake was surrounded by forest or huge and strange salt pans; and if it suffocated from anoxia or was heavily oxygenated.

There are some important exceptions to the Lacustrin theme of fossil insects, the best known being the late Jurassic limestones from Solnhofen and Eichstätt, which are marine. These deposits are famous for pterosaurs and the earliest bird, Archeopteryx. The limestones were formed by a very fine calcite mud that settled in standing, hypersaline bays that were isolated from the inland seas. Most of the organisms in these limestones, including rare insects, remained intact, sometimes with feathers and outlines of soft wing membranes, indicating that there was very little decay. The insects, however, are like casts or molds, have relief, but few details. In some cases, iron oxides precipitated around the wing veins, revealing better details.

Compressions, impressions and mineralization

There are many different ways that insects can be fossilized and preserved, including compressions and imprints, concretions, mineral replication, charred (fusainized) remains and their trace remains. Compressions and impressions are the most extensive types of insect fossils found in rocks from the Carboniferous to the Holocene. Impressions are like a cast or shape of a fossil insect and show its shape and even some relief, like folds in the wings, but usually little or no color from the cuticle. Remnants of the cuticle are retained through compressions, so that the color characterizes the structure. In exceptional situations, microscopic features such as microtrichia are even visible on sclerites and wing membranes, but maintaining this scale also requires a matrix with exceptionally fine grain, such as in micritic muds and volcanic tuffs. Since arthropod sclerites are held together by membranes that decompose easily, many fossil arthropods are only known to isolated sclerites. Complete fossils are far more desirable. Concretions are stones with a fossil in their core, the chemical composition of which is different from that of the surrounding matrix, usually formed by mineral precipitation from decaying organisms. The most significant deposit consists of various locations of the late Francis Creek carbonaceous shale of the Carbondale Formation in Mazon Creek, Illinois, which consists of shales and coal seams that form elongated concretions. Most concretions have a mold of an animal and sometimes a plant that is usually of marine origin.

When an insect is partially or completely replaced with minerals, which are usually fully articulated and three-dimensionally accurate, it is called one Mineral replication . This is also known as petrification, like petrified wood. Insects preserved in this way are often, but not always, preserved as concretions or in nodules of minerals that have formed around the insect as a core. Such deposits generally form where the sediments and water are loaded with minerals and where there is also rapid mineralization of the carcass by layers of bacteria.

Evolutionary history

The insect fossil record goes back around 400 million years to the lower Devonian, while the pterygotes (winged insects) in the Carboniferous were exposed to strong radiation. The Endopterygota was again strongly irradiated in the Permian. Survivors of the mass extinction at the PT border developed into the essentially modern insect orders in the Triassic, which have persisted into modern times.

Most modern families of insects appeared in the Jurassic, and another variety, probably genera, appeared in the Cretaceous Period. In the Tertiary there were many of the still modern genres; Hence, most of the insects in amber are actually members of existing genera. Insects diversified into essentially modern forms in only about 100 million years.

Insect development is characterized by rapid adaptation due to the selective pressure exerted by the environment and is promoted by high fertility. It appears that rapid radiation and the emergence of new species, a process that continues to this day, is causing insects to fill all available environmental niches.

The development of insects is closely related to the development of flowering plants. Insect adaptations include feeding flowers and related structures, with approximately 20% of the insects present depending on flowers, nectar, or pollen as a source of food. This symbiotic relationship is even more important in evolution when you consider that more than 2/3 of the flowering plants are pollinated by insects.

Insects, especially mosquitoes and flies, are also carriers of many pathogens that may even have been responsible for the decimation or extinction of some mammal species.

Devonian

The Devonian (419 to 359 million years ago) was a relatively warm period and there were likely to be a lack of glaciers with a reconstruction of tropical sea surface temperature from Conodont apatite, which averages 30 ° C (86 ° F) in the early Devonian. CO
2 Throughout the Devonian period, levels fell sharply as burial of newly developed forests drew carbon from the atmosphere into sediments. This can be reflected in a cooling in the central Devonian of around 5 ° C. The late Devonian warmed to a level corresponding to the early Devonian; while there is no corresponding increase in CO
2 concentrations, continental weathering increasing (as predicted by warmer temperatures); In addition, a number of clues, such as the plant distribution, point to late Devonian warming. The continent of Euramerica (or Laurussia) was created in the early Devonian by the collision of Laurentia and Baltica, which turned into the natural arid zone along the Tropic of Capricorn, formed in the Paleozoic as well as today by the convergence of two large atmospheric circulations that Hadley cell and the Ferrel cell.

The oldest definitive insect fossil is the Devonian Rhyniognatha hirsti which was estimated 407 to 396 million years ago. This species already possessed dicondylic (with two condyles, joints) mandibles, a trait associated with winged insects, suggesting that wings may have already developed by this time. The first insects, for example, probably appeared earlier in the Silurian period. Like other insects of his time Rhyniognatha presumably on plant fed sporophylls - which occur at the tips of branches and bear sporangia, the organs producing spores. The insect's anatomy could also provide clues as to what it was eating. The creature had large mandibles that may or may not have been used for hunting.

In 2012, researchers found the first complete insect in the late Devonian period (382 to 359 million years ago) in the vicinity of Strud (Gesves, Belgium) from the Bois des Mouches Formation in Oberfamennian. It had unspecialized, orthopteroid mouth parts, indicating an omnivorous diet. This discovery reduces an earlier gap of 45 million years in insect evolution that is part of the arthropod gap (the "gap" still occurs in the early Carboniferous and collapses and extends beyond the Romer gap for tetrapods that may caused by low oxygen levels in the atmosphere). Body segments, legs and antennae are visible; However, genitals were not preserved. The venerable kind was Called Strudiella devonica. The insect does not have wings, but it can be a juvenile.

Carbon

The Carboniferous (359 to 299 million years ago) is famous for its humid, warm climate and extensive swamps with mosses, ferns, horsetail and calamites. The glaciations in Gondwana triggered by Gondwana’s movement to the south continued into the Permian. Due to the lack of clear markings and fractures, the deposits of this Ice Age are often referred to as permocarbonic in old age. The cooling and drying of the climate led to the collapse of the carbonaceous rainforest (CRC). Tropical rainforests fragmented and were eventually devastated by climate change.

Remains of insects are scattered in the coal deposits, especially the wings of cockroaches (Blattodea); Two deposits in particular are from Mazon Creek, Illinois and Commentry, France. The earliest winged insects are from this period (Pterygota), including the above-mentioned Blattodea, Caloneurodea, the primitive tribe group Ephemeropterans, Orthoptera, Palaeodictyopteroidea. 1940 (in Noble County, Oklahoma) found a fossil of Meganeuropsis americana the largest complete insect wing ever found. Young insects are also known from the Carboniferous Period.

Very early leafopters had a large, disc-shaped pronotum and leather-like fore wings with a pronounced CuP vein (an unbranched wing vein that lay near the claval fold and reached the posterior edge of the wing). These weren't real cockroaches as they had an ovipositor, even though the ovipositor decreased due to the carbon. The orders Caloneurodea and Miomoptera are known, with Orthoptera and Blattodea belonging to the earliest Neoptera; Development from the Upper Carboniferous to the Permian. These insects had wings of a similar shape and structure: small anal lobes. Species of orthoptera or grasshoppers and related relatives are an ancient order that dates back to that time to this day. From this point on, the characteristic synapomorphism of the saltatorial or adaptive jumping hind legs is retained.

Palaeodictyopteroidea is a large and diverse group that comprises 50% of all known Paleozoic insects. Contains many of the primitive features of the time: very long cerci, an ovipositor, and wings with little or no anal lobe. Protodonata, as the name suggests, is a primitive paraphyletic group similar to Odonata. although there are no special features such as a nodus, a pterostigma, and an arculus. Most were only slightly larger than modern dragonflies, but the group includes the largest known insects, such as the late Carboniferous Meganeura monyi , Mega type and the even greater later Permian Meganeuropsis permiana with wing spans of up to 71 cm). They were probably the best predators for around 100 million years and were far larger than any insect today. Your nymphs must also be very impressive in size. This gigantism could be due to higher atmospheric oxygen values ​​(up to 80% above modern values ​​during the Carboniferous), which enabled greater breathing efficiency compared to today. The lack of flying vertebrates could have been another factor.

Permian

The Permian (299 to 252 million years ago) was a relatively short period of time during which all of the Earth's major land masses were gathered on a single supercontinent called Pangea. Pangea spanned the equator and extended towards the poles, which had corresponding effects on the ocean currents in the single great ocean ("Panthalassa", the "universal sea") and in the Paleo-Tethys Ocean, a great ocean between Asia and Gondwana . The continent of Cimmeria rifted away from Gondwana and drifted north to Laurasia, shrinking the Paleo-Tethys. At the end of the Permian, the largest mass extinction in history occurred, known as the Permian Triassic Extinction: 30% of all insect species became extinct; This is one of three known mass extinctions of insects in the history of the earth.

2007 study, based on DNA from living beetles and maps of probable beetle evolution, indicated that beetles emerged during the lower its Permian, up to 299 million years. In 2009, a fossil beetle from Mazon Creek, Illinois, Pennsylvania was described that traced the beetle's origin to an earlier point in time between 318 and 299 million years ago. Fossils from this period have been found in Asia and Europe, for example in the fossil beds made of red slate from Niedermoschel near Mainz. Other fossils have been found in Obora, Czech Republic and Tshekarda in the Urals, Russia. Further discoveries from North America were made in the Wellington Formation of Oklahoma and published in 2005 and 2008. Some of the most important fossil deposits from this period come from Elmo, Kansas (260 mya); Others are New South Wales, Australia (240 mya), and Central Eurasia (250 mya).

During this time, many species diversified from the Carboniferous and many new orders developed, including: Protelytroptera, primitive relatives of Plecoptera (Paraplecoptera), Psocoptera, Mecoptera, Coleoptera, Raphidioptera, and Neuroptera, the last four being the first definitive record of the Holometabola. Among the Pennsylvanians and well into the Permian, primitive Blattoptera or relatives of cockroaches were by far the most successful. Six quick legs, two well-developed folding wings, pretty good eyes, long, well-developed antennae (olfactory), an omnivorous digestive system, a container for storing sperm, a chitin skeleton that can support and protect, and some form of gizzard and efficient Mouth parts gave it tremendous advantages over other herbivorous animals. About 90% of the insects were cockroach-like insects ("Blattopterans"). The dragonflies Odonata were the dominant aerial predator and probably also the predator of land insects. True odonata appeared in the Permian and all are amphibians. Their prototypes are the oldest winged fossils, date back to the Devonian and differ in every way from other wings. Their prototypes may have had the beginnings of many modern attributes as early as the late Carboniferous, and it is possible that they even captured small vertebrates, as some species had a wingspan of 71 cm.

The oldest known insect that resembles Coleopteran species is from the Lower Permian (270 million years ago), although it instead has 13-segmented antennae, elytra with a more developed venation and more irregular longitudinal ribs, and a protruding abdomen and ovipositor at the tip of the Elytra. The oldest true beetle would have features that included 11-segmented antennae, regular longitudinal ribs on the elytra, and internal genitalia. The earliest beetle-like species had pointed, leathery fore wings with cells and pits. Hemiptera, or true beetles, had appeared in the form of Arctiniscytina and Paraknightia. The latter had dilated parapronotal lobes, a large ovipositor, and fore wings with unusual venation that may differ from Blattoptera. The orders Raphidioptera and Neuroptera are combined as Neuropterida. One family of the putative raphidiopteran clade (Sojanoraphidiidae) has been controversially classified as such. The group had a long ovipositor, characteristic of this order, and a series of short cross veins, but with a primitive wing vein. Early families of Plecoptera had winged veins consistent with the Order and its youngest offspring. Psocoptera first appeared in the Permian Period, they are often considered to be the most primitive of the hemipteroids.

Triad

The Triassic (252 to 201 million years ago) was a time when developed in arid and semi-arid savannas and when the first mammals, dinosaurs and pterosaurs also appeared. During the Triassic, almost all of the earth's landmass was still concentrated in Pangea. A huge gulf penetrated Pangea, the Tethys Sea, from the east. The remaining banks were surrounded by the world ocean Panthalassa. The supercontinent of Pangea ruptured during the Triassic - especially late in the period - but had not yet separated.

The Triassic climate was generally hot and dry, with red bed typically formed by sandstones and evaporites. There is no evidence of icing on or near any of the poles. In fact, the polar regions appeared to be humid and temperate, a climate suitable for reptile-like creatures. The size of Pangea limited the mitigating effects of the global ocean; The continental climate was very seasonal with very hot summers and cold winters. It probably had strong, cross-equatorial monsoons.

As a result of the P-Tr mass extinction on the Permian-Triassic border, there are few fossil records of insects, including Lower Triassic beetles. However, there are some exceptions, as in Eastern Europe: At the Babiy Kamen site in the Kuznetsk Basin, numerous beetle fossils were discovered, even entire specimens of the infraorder Archostemata (i.e. Ademosynidae, Schizocoleidae), Adephaga (i.e. Triaplidae, Trachypachidae)) and Polyphaga (i.e. Hydrophilidae, Byrrhaga , Elateroidea) and in an almost perfectly preserved condition. Species from the families Cupedidae and Schizophoroidae are not present at this point, while they dominate other fossil sites from the Lower Triassic. Other records are known from Khey-Yaga, Russia, in the Korotaikha Basin.

It was around this time, during the Late Triassic, that myketophageal or fungus-eating species of beetles (i.e. Cupedidae) appear in the fossil record. In the stages of the Upper Triassic, representatives of the algophagic or algae-eating species (i.e. Triaplidae and Hydrophilidae), as well as predatory water beetles, appear. The first primitive weevils appear (ie Obrienidae) as well as the first representatives of the ground beetles (ie Staphylinidae), which do not show a clear difference in body structure compared to newer species. This was also about the first time that evidence of a diverse freshwater insect fauna appeared.

Some of the oldest living families also emerge during the Triassic. To the Hemiptera included the Cercopidae, Cicadellidae, Cixiidae, and Membracidae. To the Coleoptera included the Carabidae, Staphylinidae, and Trachypachidae. Hymenoptera included the Xyelidae. Diptera included the Anisopodidae, the Chironomidae, and the Tipulidae. The first Thysanoptera also appeared.

The first true Diptera species are known from the Middle Triassic and spread in the Middle and Late Triassic. In Australia (Mt. Crosby) a single large wing of a Diptera species was found in the Triassic (10 mm instead of the usual 2-6 mm). This family Tilliardipteridae should be included in Psychodomorpha sensu Hennig despite the numerous "tipuloid" properties, since the convex distal 1A reaches the edge of the wing and the anal loop is formed.

law

The Jurassic (201 to 145 million years ago) was important for the development of birds, one of the largest insect predators. During the early Jurassic period, the supercontinent Pangea split up into the northern supercontinent Laurasia and the southern supercontinent Gondwana; The Gulf of Mexico opened in the new rift between North America and what is now Mexico's Yucatan Peninsula. The Jurassic North Atlantic was relatively narrow, while the South Atlantic did not open until the following Cretaceous period, when Gondwana itself tore apart.

The global climate during the Jura was warm and humid. Similar to the Triassic, there were no major land masses near the polar caps and consequently there were no inland shields during the Jurassic. Although some areas of North and South America and Africa remained dry, large parts of the continental land masses were lush. The Laurasian and Gondwanian fauna differed significantly in the early Jurassic. Later it became more intercontinental and many species began to spread around the world.

There are many key sites from the Jurassic with more than 150 key sites with beetle fossils, most of them in Eastern Europe and Northern Asia. In North America, and particularly in South America and Africa, the number of sites from this period is lower and the sites have not yet been fully investigated. The outstanding fossils include Solnhofen in Upper Bavaria, Karatau in southern Kazakhstan, the Yixian Formation in Liaoning, northern China and the Jiulongshan Formation and other fossils in Mongolia. There are few sites in North America with fossil records of insects from the Jurassic, namely the limestone deposits in the Hartford Basin, Deerfield Basin, and Newark Basin. Numerous deposits of other insects occur in Europe and Asia. Including Grimmen and Solnhofen, German; Solnhofen is famous for finding the earliest birds (i.e. Archeopteryx). Others include Dorset, England; Issyk-Kul, Kyrgyzstan; and the most productive location of them all, Karatau, Kazakhstan.

During the Jurassic, the known family-level coleopteran diversity increased dramatically. This includes the development and growth of carnivorous and herbivorous species. It is believed that species of the superfamily Chrysomeloidea evolved at the same time, which includes a wide range of plant hosts ranging from cycads and conifers to angiosperms. In the vicinity of the Upper Jurassic the proportion of Cupedidae decreased, but at the same time the diversity of early herbivores or phytophagous species increased. Most of the youngest phytophagous species of Coleoptera feed on flowering plants or angiosperms.

chalk

The Cretaceous Period (145 to 66 million years ago) had the same insect fauna as the Jurassic until much later. During the Cretaceous Period, the late-Paleozoic-to-Early Mesozoic supercontinent of Pangea, its tectonic division into present-day continents, although their positions were substantially different at the time. As the Atlantic expanded, the convergent-margin orogeny that had begun during the Jurassic in the wider North American Cordilleras, when Nevadan orogeny was followed by the Sevier and Laramide orogeny. Though Gondwana was still intact at the beginning of the Cretaceous Period, it disintegrated as South America, Antarctica, and Australia drifted away from Africa (although India and Madagascar remained tied). Thus the South Atlantic and the Indian Ocean were newly formed. Such active rifts raised large underwater mountain ranges along the welts and raised eustatic sea levels worldwide. The Tethys Sea narrowed further in northern Africa. The wide shallow sea spread across Central North America (Western Interior Seaway) and Europe and then receded late in time, leaving thick marine deposits between coal beds.

At the height of the Chalk Crossing, a third of today's land area was submerged. The Berriasian epoch showed a cooling trend that had been observed in the last epoch of the Jurassic. There is evidence that snowfalls were frequent at higher latitudes and that the tropics became more humid than during the Triassic and Jurassic. However, glaciation has been limited to alpine glaciers in some high latitude mountains, although seasonal snow may have been further south. Rafting of rocks with ice in marine environments occurred during much of the Cretaceous Period, but evidence of deposit directly from glaciers is limited to the early Cretaceous Period of the Eromanga Basin in South Australia.

There are a large number of important fossil sites around the world that contain Cretaceous beetles. Most of them are located in Europe and Asia and belong to the temperate climatic zone during the Cretaceous Period. Some of the fossils mentioned in the Jurassic chapter also document the early chalk beetle fauna (e.g. the Yixian Formation in Liaoning, northern China). Other important locations from the Lower Cretaceous include the Crato fossil beds in the Araripe Basin in Ceará, northern Brazil, as well as the Santana Formation above, the latter being near the paleoequator, or the position of the Earth's equator in the geological past as defined for a certain geological period. In Spain there are major tourist attractions near Montsec and Las Hoyas. In Australia, the Koonwarra fossil beds of the Korumburra group in South Gippsland, Victoria, are noteworthy. Important fossils from the Upper Cretaceous are Kzyl-Dzhar in southern Kazakhstan and Arkagala in Russia.

During the Cretaceous Period, the variety of Cupedidae and Archostemata decreased significantly. Predatory ground beetles (Carabidae) and rove beetles (Staphylinidae) began to distribute in different patterns: while the Carabidae occurred predominantly in the warm regions, the Staphylinidae and beetles (Elateridae) preferred many areas with a temperate climate. Predatory species of Cleroidea and Cucujoidea also hunted their prey under the bark of trees together with the jewel beetles (Buprestidae). The variety of jewel beetles increased rapidly during the Cretaceous period, as they were the main consumers of wood, while longhorn beetles (Cerambycidae) were rather rare and their diversity only increased towards the end of the Upper Cretaceous. The first coprophage beetles come from the Upper Cretaceous and are said to have lived on the excrement of herbivorous dinosaurs. However, it is still debated whether the beetles were always attached to mammals during their development. The first species are also found in which both larvae and adults are adapted to the aquatic lifestyle. Vertebrate beetles (Gyrinidae) were moderately diverse, although other early beetles (i.e., Dytiscidae) were less, with the most common species being the Coptoclavidae, which hunted water fly larvae.

Paleogene

Many beetle fossils are known from this period, although the beetle fauna of the Paleocene has been comparatively poorly studied. In contrast, knowledge about the beetle fauna of the Eocene is very good. The reason is the occurrence of fossil insects in amber and slate sediments. Amber is petrified tree resin, meaning it consists of petrified organic compounds, not minerals. Different amber differs according to the location, age and type of resin-producing plant. Baltic and Dominican amber is most important for research into the beetle fauna of the Oligocene. Even if the records of insect fossils are generally absent, the most diverse deposit is from the Fur Formation, Denmark; including giant ants and primitive moths (Noctuidae).

The first butterflies come from the Upper Paleogene, while most, like beetles, had newer genera and species as early as the Miocene. However, their distribution differed significantly from today's.

Neogene

The most important locations for beetle fossils of the Neogene are in the warm temperate and subtropical zones. Many newer genera and species already existed in the Miocene, but their distribution differed considerably from today's. One of the most important fossil sites for insects of the Pliocene is Willershausen near Göttingen with its excellently preserved beetle fossils from different families (longhorn beetles, weevils, ladybirds and others) as well as representatives of other insect orders. So far, 35 genera from 18 beetle families have been recorded in the Willershausen clay pit, six of which have become extinct. The beetle fauna of the Pleistocene is relatively well known.She used the composition of the beetle fauna to reconstruct the climatic conditions in the Rocky Mountains and on Beringia, the former land bridge between Asia and North America.

Phylogeny

A report in November 2014 clearly assigned the insects to a clade, with the remipedes being the closest sister clade. This study resolved the insect phylogeny of all existing insect orders and provided "a robust phylogenetic backbone tree and reliable time estimates of insect development". Finding strong support for the hexapod's closest living relatives had proven difficult because of the convergent adaptations in a number of arthropod groups for life on land.

In 2008, researchers at Tufts University discovered what they believed to be the oldest known full-body print of a primitive flying insect in the world, a 300 million year old specimen from the Carboniferous Age. The oldest definitive insect fossil is the Devonian Rhyniognatha Hirsti from the 396 million year old Rhynie Chert. It might on the surface have resembled a modern silverfish insect. This species already possessed dicondylic mandibles (two articulations in the lower jaw), a trait associated with winged insects, suggesting that wings may have already developed by this point. The first insects, for example, probably appeared earlier in the Silurian period. There were four super-radiations from insects: beetles (developed about 300 million years ago), flies (developed about 250 million years ago), moths and wasps (developed about 150 million years ago). These four groups make up the majority of the species described. The flies and moths along with the fleas evolved from the Mecoptera. The origins of insect flight remain unclear as the earliest currently known winged insects appear to be able fliers. Some extinct insects had an additional pair of winglets that were attached to the first segment of the thorax for a total of three pairs. There is no evidence that the insects were a particularly successful group of animals before they developed into wings.

Evolutionary relationships

Insects are prey for a wide variety of organisms, including terrestrial vertebrates. The earliest land-based vertebrates existed 350 million years ago and were large amphibious fish-eaters. Through gradual evolutionary changes, insect fruit was the next type of diet to evolve. Insects were among the earliest terrestrial herbivores and acted as important means of selection for plants. Plants developed chemical defenses against this herbivore and the insects in turn developed mechanisms to deal with plant toxins. Many insects use these toxins to protect themselves from their predators. Such insects often use warning colors to advertise their toxicity. This successful evolutionary pattern was also used by facial expressions. Over time, this has resulted in complex groups of co-evolved species. Conversely, some interactions between plants and insects, such as pollination, are beneficial for both organisms. Coevolution has led to the development of very specific reciprocities in such systems.

Taxonomy

Phylogenetic relationship of some common insect orders: Thysanura, Odonata, Orthoptera, Phasmatodea, Blattodea, Isoptera, Hemiptera, Coleoptera, Hymenoptera, Lepidoptera, Diptera. No information should be derived from the branch length.

The traditional morphology-based or appearance-based systematics has usually given Hexapoda the rank of an upper class and identified four groups in it: insects (Ectognatha), springtails (Collembola), protura and diplura, the last three being summarized on this basis as entognatha of internalized Mouth parts. Supra-ordinal relationships have undergone numerous changes with the advent of methods based on evolutionary history and genetic data. A more recent theory is that Hexapoda is polyphyletic (where the last common ancestor was not a member of the group), with the Entognath classes having separate evolutionary histories from Insecta. Many of the traditional taxa based on appearance have been shown to be paraphyletic. Instead of using ranks like subclass, superorder, and infraorder, it has been found better to use monophyletic groupings (where the last common ancestor is a member of the group). The following represents the best supported monophyletic groupings for the Insecta.

Insects can be divided into two groups that have historically been treated as subclasses: wingless insects known as apterygota and winged insects known as pterygota. The Apterygota consist of the primitive wingless order of the silver fish (Thysanura). Archeognatha form the monocondylia based on the shape of their mandibles, while Thysanura and Pterygota are grouped together as Dicondylia. It is possible that the Thysanura themselves are not monophyletic, with the Lepidotrichidae family being a sister group of the Dicondylia (Pterygota and the remaining Thysanura).

Paleoptera and Neoptera are the winged orders of insects that differ by the presence of hardened body parts called sclerites. also in neoptera muscles that allow their wings to fold flat over the abdomen. Neoptera can be further divided into incomplete metamorphosis-based (Polyneoptera and Paraneoptera) and complete metamorphosis-based groups. It has proven difficult to clarify the relationships between the orders in Polyneoptera, as new knowledge is constantly emerging that requires a revision of the taxa. For example, Paraneoptera has been found to be more closely related to Endopterygota than to the rest of the Exopterygota. The latest molecular finding that the traditional louse orders Mallophaga and Anoplura originate from Psocoptera has led to the new taxon Psocodea. It has been suggested that Phasmatodea and Embiidina form eukinolabia. It is believed that Mantodea, Blattodea, and Isoptera form a monophyletic group called Dictyoptera.

It is likely that Exopterygota is paraphyletic with respect to Endopterygota. Controversial issues include Strepsiptera and Diptera, which have been grouped together as Halteria due to a reduction in one of the pairs of wings - a position that is not well supported in the entomological community. The Neuropterida are often grouped or split according to the whims of the taxonomist. It is believed that fleas are now closely related to boride mecopterans. Many questions still need to be answered when it comes to basic relationships between endopterygotic orders, especially Hymenoptera.

The study of the classification or taxonomy of an insect is called systematic entomology. When working with a more specific order or even a family, the term can also be made specific to that order or family, for example systematic dipterology.

Early evidence

The oldest definitive insect fossil is the Devonian Rhyniognatha hirsti , which is estimated to be 396 to 407 million years old. This species already possessed dicondylic mandibles, a trait associated with winged insects, suggesting that wings may have already developed by this point. The first insects, for example, probably appeared earlier in the Silurian period.

The subclass Apterygota (wingless insects) is now considered artificial, since the silverfish (order Thysanura) are more closely related to pterygota (winged insects) than to bristle tails (order Archeognatha). For example, just like flying insects, Thysanura have so-called dicondylic mandibles, while Archaeognatha have monocondylic mandibles. The reason for their resemblance is not that they are particularly closely related, but that both have retained a primitive and original anatomy to a much greater extent than the winged insects. The most primitive order of flying insects, the mayflies (Ephemeroptera), are also those most morphologically and physiologically similar to these wingless insects. Some mayfly nymphs resemble water thysanurans.

Modern Archaeognatha and Thysanura still have rudimentary appendages on their abdomen called pegs, while more primitive and extinct insects known as monura had much more developed abdominal appendages. The belly and chest segments of the earliest terrestrial ancestor of the insects would have been more similar than they are today, and the head had well-developed compound eyes and long antennae. Your height is not yet known. Since the most primitive group today, Archaeognatha, are most abundant near the coast, it could mean that this was the type of habitat where the ancestors of the insects became terrestrial. But this specialization in coastal niches could also have a secondary origin, as could their jumping locomotion, as it is the crawling Thysanura that can be considered most original (plesiomorphic). If you look at how primitive cheliceratan book gills (still seen in horseshoe crabs) evolved into book lungs in primitive spiders and eventually trachea in more advanced spiders (most of them still have a pair of book lungs intact), it is possible to die Insect trachea was formed in a similar manner, with the gills at the base of their limbs modified.