Evolution has produced astonishing variety in insects. Pictured are Evolution of insects From Wikipedia, the free encyclopedia Based on genome sequencing data, it is estimated that the class of insects originated on Earth about 480 million years ago, in the Ordovician, at about the same time terrestrial plants appeared.[1] Insects evolved from a group of crustaceans.[2] The first insects were land bound, but about 400 million years ago in the Devonian period one lineage of insects evolved flight, the first animals to do so.[1] The oldest definitive insect fossil, Rhyniognatha hirsti, is estimated to be 407 to 396 million years old. Global climate conditions changed several times during the history of Earth, and along with it the diversity of insects. The Pterygotes (winged insects) underwent a major radiation in the Carboniferous (356 to 299 million years ago) while the Endopterygota (insects that go through different life stages with metamorphosis) underwent another major radiation in the Permian (299 to 252 million years ago). Most extant orders of insects developed during the Permian period. Many of the early groups became extinct during the mass extinction at the Permo-Triassic boundary, the largest extinction event in the history of the Earth, around 252 million years ago.[3] The survivors of this event evolved in the Triassic (252 to 201 million years ago) to what are essentially the modern insect orders that persist to this day. Most modern insect families appeared in the Jurassic (201 to 145 million years ago). In an important example of co-evolution, a number of highly successful insect groups — especially the Hymenoptera (wasps, bees and ants) and Lepidoptera (butterflies) as well as Page 1 of 39 Evolution of insects - Wikipedia 1/2/2017 https://en.wikipedia.org/wiki/Evolution_of_insects some of the possible shapes of antennae. many types of Diptera (flies) and Coleoptera (beetles) — evolved in conjunction with flowering plants during the Cretaceous (145 to 66 million years ago).[4] Many modern insect genera developed during the Cenozoic that began about 65 million years ago; insects from this period onwards frequently became preserved in amber, often in perfect condition. Such specimens are easily compared with modern species, and most of them are members of extant genera. Contents ◾ 1 Fossils ◾ 2 Evolutionary history ◾ 2.1 Devonian ◾ 2.2 Carboniferous ◾ 2.3 Permian ◾ 2.4 Triassic ◾ 2.5 Jurassic ◾ 2.6 Cretaceous ◾ 2.7 Paleogene ◾ 2.8 Neogene ◾ 3 Phylogeny ◾ 3.1 Evolutionary relationships ◾ 4 Taxonomy ◾ 5 Early evidence ◾ 5.1 Odonata ◾ 6 Origin of insect flight ◾ 6.1 Theories ◾ 7 Life cycle ◾ 7.1 Mayflies ◾ 7.2 Distant ancestors ◾ 8 See also Page 2 of 39 Evolution of insects - Wikipedia 1/2/2017 https://en.wikipedia.org/wiki/Evolution_of_insects ◾ 9 References ◾ 10 External links Fossils Insect fossils are not merely impressions, but also appear in many other forms; While wings are indeed a common insect fossil, they do not readily decay or digest, which is why birds and spiders typically leave the wings after devouring the rest of an insect. Terrestrial vertebrates are almost always preserved just as bony remains (or inorganic casts thereof), the original bone usually having been replaced by the mineral apatite. Occasionally, mummified or frozen vertebrates are found, but their age is usually no more than several thousand years. Fossils of insects, in contrast, are preserved as three- dimensional, permineralized, and charcoalified replicas; and as inclusions in amber and even within some minerals. There is also abundant fossil evidence for the behavior of extinct insects, including feeding damage on fossil vegetation and in wood, fecal pellets, and nests in fossil soils. Dinosaur behavior, by contrast, is recorded mostly as footprints and coprolites.[5]:42 The common denominator among most deposits of fossil insects and terrestrial plants is the lake environment. Those insects that became preserved were either living in the fossil lake (autochthonous) or carried into it from surrounding habitats by winds, stream currents, or their own flight (allochthonous). Drowning and dying insects not eaten by fish and other predators settle to the bottom, where they may be preserved in the lake’s sediments, called lacustrine, under appropriate conditions. Even amber, or fossil resin from trees, requires a watery environment that is lacustrine or brackish in order to be preserved. Without protection in anoxic sediments, amber would gradually disintegrate; it is never found buried in fossil soils. Various factors contribute greatly to what kinds of insects become preserved and how well, if indeed at all, including lake depth, temperature, and alkalinity; type of sediments; whether the lake was surrounded by forest or vast and featureless salt pans; and if it was choked in anoxia or highly Page 3 of 39 Evolution of insects - Wikipedia 1/2/2017 https://en.wikipedia.org/wiki/Evolution_of_insects oxygenated. There are some major exceptions to the lacustrine theme of fossil insects, the most famous being the Late Jurassic limestones from Solnhofen and Eichstätt, Germany, which are marine. These deposits are famous for pterosaurs and the earliest bird, Archaeopteryx. The limestones were formed by a very fine mud of calcite that settled within stagnant, hypersaline bays isolated from inland seas. Most organisms in these limestones, including rare insects, were preserved 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, having relief but little detail. In some cases iron oxides precipitated around wing veins, revealing better detail.[5]:42 There are many different ways insects can be fossilized and preserved, one which includes compressions and impressions, concretions, mineral replication, charcoalified (fusainized) remains, and their trace remains. Compressions and Impressions are the most extensive types of insect fossils, occurring in rocks from the Carboniferous to Recent. Impressions are like a cast or mold of a fossil insect, showing its form and even some relief, like pleating in the wings, but usually little or no color from the cuticle. Compressions preserve remains of the cuticle, so color distinguishes structure. In exceptional situations, microscopic features such as microtrichia on sclerites and wing membranes are even visible, but preservation of this scale also requires a matrix of exceptionally fine grain, such as in micritic muds and volcanic tuffs. Because arthropod sclerites are held together by membranes, which readily decompose, many fossil arthropods are known only by isolated sclerites. Far more desirable are complete fossils. Concretions are stones with a fossil at the core whose chemical composition differs from that of the surrounding matrix, usually formed as a result of mineral precipitation from decaying organisms. The most significant deposit consists of various localities of the Late Carboniferous Francis Creek Shale of the Carbondale Formation at Mazon Creek, Illinois, which are composed of shales and coal seams yielding oblong concretions. Within most concretions is a mold of an animal and sometimes a plant that is usually marine in origin. Page 4 of 39 Evolution of insects - Wikipedia 1/2/2017 https://en.wikipedia.org/wiki/Evolution_of_insects When an insect is partly or wholly replaced by minerals, usually completely articulated and with three-dimensional fidelity, is called Mineral replication. This is also called petrifaction, as in “petrified” wood. Insects preserved this way are often, but not always, preserved as concretions, or within nodules of minerals that formed around the insect as its nucleus. Such deposits generally form where the sediments and water are laden with minerals, and where there is also quick mineralization of the carcass by coats of bacteria. Evolutionary history The insect fossil record extends back some 400 million years to the lower Devonian, while the Pterygotes (winged insects) underwent a major radiation in the Carboniferous. The Endopterygota underwent another major radiation in the Permian. Survivors of the mass extinction at the PT boundary evolved in the Triassic to what are essentially the modern Insecta Orders that persist to modern times. Most modern insect families appeared in the Jurassic, and further diversity probably in genera occurred in the Cretaceous. By the Tertiary, there existed many of what are still modern genera; hence, most insects in amber are, indeed, members of extant genera. Insects diversified in only about 100 million years into essentially modern forms.[6] Insect evolution is characterized by rapid adaptation with selective pressures exerted by environment, with rapid adaptation being furthered by their high fecundity. It appears that rapid radiations and the appearance of new species, a process that continues to this day, result in insects filling all available environmental niches. Insect evolution is closely related to the evolution of flowering plants. Insect adaptations include feeding on flowers and related structures, with some 20% of extant insects depending on flowers, nectar or pollen for their food source. This symbiotic relationship is even more paramount in evolution considering that about 2/3 of flowering plants are insect pollinated. Insects are also vectors of many pathogens that may even have been responsible for the decimation or extinction of some mammalian species. Compared to other organisms, insects have not left a particularly robust fossil record. Other than in amber, most insects are terrestrial and only Page 5 of 39 Evolution of insects - Wikipedia 1/2/2017 https://en.wikipedia.org/wiki/Evolution_of_insects preserved under very special conditions such as at the edge of freshwater lakes. Yet in amber, age is limited since large resin production by trees developed later than the ancient insects. Interestingly, while some 1/3 of non- insect species are extinct fossils, it is believed that only 1/100th insects are extinct fossils.[6] Devonian The Devonian (419 to 359 million years ago) was a relatively warm period, and probably lacked any glaciers with reconstruction of tropical sea surface temperature from conodont apatite implying an average value of 30 °C (86 °F) in the Early Devonian. CO2 levels dropped steeply throughout the Devonian period as the burial of the newly evolved forests drew carbon out of the atmosphere into sediments; this may be reflected by a Mid-Devonian cooling of around 5 °C (9 °F). The Late Devonian warmed to levels equivalent to the Early Devonian; while there is no corresponding increase in CO2 concentrations, continental weathering increases (as predicted by warmer temperatures); further, a range of evidence, such as plant distribution, points to Late Devonian warming.[7] The continent Euramerica (or Laurussia) was created in the early Devonian by the collision of Laurentia and Baltica, which rotated into the natural dry zone along the Tropic of Capricorn, which is formed as much in Paleozoic times as nowadays by the convergence of two great atmospheric circulations, the Hadley cell and the Ferrel cell. The oldest definitive insect fossil is the Devonian Rhyniognatha hirsti, estimated at 407 to 396 million years ago.[8] This species already possessed dicondylic mandibles, a feature associated with winged insects, suggesting that wings may already have evolved at this time. Thus, the first insects probably appeared earlier, in the Silurian period.[8][9] Like other insects of its time, Rhyniognatha presumably fed on plant sporophylls — which occur at the tips of branches and bear sporangia, the spore-producing organs. The insect’s anatomy might also give clues as to what it ate. The creature had large mandibles which may or may not have been used for hunting.[8] Page 6 of 39 Evolution of insects - Wikipedia 1/2/2017 https://en.wikipedia.org/wiki/Evolution_of_insects In 2012, researchers found the first complete insect in the Late Devonian period (382 to 359 million years ago), in the Strud (Gesves, Belgium) environment from the Bois des Mouches Formation, Upper Famennian. It had unspecialized, 'orthopteroid' mouthparts, indicating an omnivorous diet. This discovery reduces a previous gap of 45 million years in the evolutionary history of insects, part of the arthropod gap (the 'gap' still occurs in the early Carboniferous, coinciding and extending past the Romer's gap for tetrapods, which may have been caused by low oxygen levels in the atmosphere).[10] Body segments, legs and antennae are visible; however, genitalia were not preserved. The new fossil was named Strudiella devonica; it represents a new species as well.[11] The insect has no wings, but it may be a juvenile.[11] Carboniferous The Carboniferous (359 to 299 million years ago) is famous for its wet, warm climates and extensive swamps of mosses, ferns, horsetails, and calamites.[9] Glaciations in Gondwana, triggered by Gondwana's southward movement, continued into the Permian and because of the lack of clear markers and breaks, the deposits of this glacial period are often referred to as Permo- Carboniferous in age. The cooling and drying of the climate led to the Carboniferous Rainforest Collapse (CRC). Tropical rain forests fragmented and then were eventually devastated by climate change.[12] Remains of insects are scattered throughout the coal deposits, particularly of wings from cockroaches (Blattodea);[13] two deposits in particular are from Mazon Creek, Illinois and Commentry, France.[14] The earliest winged insects are from this time period (Pterygota), including the aforementioned Blattodea, Caloneurodea, primitive stem-group Ephemeropterans, Orthoptera, Palaeodictyopteroidea.[9]:399 In 1940 (in Noble County, Oklahoma), a fossil of Meganeuropsis americana represented the largest complete insect wing ever found.[15] Juvenile insects are also known from the Carboniferous Period.[16] Page 7 of 39 Evolution of insects - Wikipedia 1/2/2017 https://en.wikipedia.org/wiki/Evolution_of_insects Very early Blattopterans had a large, discoid pronotum and coriaceous forewings with a distinct CuP vein (a unbranched wing vein, lying near the claval fold and reaching the wing posterior margin). These were not true cockroaches, as they had an ovipositor, although through the Carboniferous, the ovipositor started to diminish. The orders Caloneurodea and Miomoptera are known, with Orthoptera and Blattodea to be among the earliest Neoptera; developing from the upper Carboniferous to the Permian. These insects had wings with similar form and structure: small anal lobes.[9]:399 Species of Orthoptera, or grasshoppers and related kin, is an ancient order that still exist till today extending from this time period. From which time even the distinctive synapomorphy of saltatorial, or adaptive for jumping, hind legs is preserved. Palaeodictyopteroidea is a large and diverse group that includes 50% of all known Paleozoic insects.[5] Containing many of the primitive features of the time: very long cerci, an ovipositor, and wings with little or no anal lobe. Protodonata, as its name implies, is a primitive paraphyletic group similar to Odonata; although lacks distinct features such as a nodus, a pterostigma and an arculus. Most were only slightly larger than modern dragonflies, but the group does include the largest known insects, such as the late Carboniferous Meganeura monyi, Megatypus, and the even larger later Permian Meganeuropsis permiana, with wingspans of up to 71 centimetres (2.33 ft). They were probably the top predators for some 100 million years[9]:400 and far larger than any present-day insects. Their nymphs must also have reached a very impressive size. This gigantism may have been due to higher atmospheric oxygen-levels (up to 80% above modern levels during the Carboniferous) that allowed increased respiratory efficiency relative 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 time period, during which all the Earth's major land masses were collected into a single supercontinent known as Pangaea. Pangaea straddled the equator and Page 8 of 39 Evolution of insects - Wikipedia 1/2/2017 https://en.wikipedia.org/wiki/Evolution_of_insects extended toward the poles, with a corresponding effect on ocean currents in the single great ocean ("Panthalassa", the "universal sea"), and the Paleo- Tethys Ocean, a large ocean that was between Asia and Gondwana. The Cimmeria continent rifted away from Gondwana and drifted north to Laurasia, causing the Paleo-Tethys to shrink.[9]:400 At the end of the Permian, the biggest mass extinction in history occurred, collectively called the Permian–Triassic extinction event: 30% of all insect species became extinct; this is one of three known mass insect extinctions in Earth's history.[17] 2007 study based on DNA of living beetles and maps of likely beetle evolution indicated that beetles may have originated during the Lower Permian, up to 299 million years ago.[18] In 2009, a fossil beetle was described from the Pennsylvanian of Mazon Creek, Illinois, pushing the origin of the beetles to an earlier date, 318 to 299 million years ago.[19] Fossils from this time have been found in Asia and Europe, for instance in the red slate fossil beds of Niedermoschel near Mainz, Germany.[20] Further fossils have been found in Obora, Czech Republic and Tshekarda in the Ural mountains, Russia. [21] However, there are only a few fossils from North America before the middle Permian, although both Asia and North America had been united to Euramerica. The first discoveries from North America were made in the Wellington formation of Oklahoma and were published in 2005 and 2008. [17][22] Some of the most important fossil deposits from this era are from Elmo, Kansas (260 mya); others include New South Wales, Australia (240 mya) and central Eurasia (250 mya).[9]:400 During this time, many of the species from the Carboniferous diversified, 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 records of the Holometabola.[9]:400 By the Pennsylvanian and well into the Permian, by far the most successful were primitive Blattoptera, or relatives of cockroaches. Six fast legs, two well-developed folding wings, fairly good eyes, long, well- developed antennae (olfactory), an omnivorous digestive system, a receptacle Page 9 of 39 Evolution of insects - Wikipedia 1/2/2017 https://en.wikipedia.org/wiki/Evolution_of_insects for storing sperm, a chitin skeleton that could support and protect, as well as a form of gizzard and efficient mouth parts, gave it formidable advantages over other herbivorous animals. About 90% of insects were cockroach-like insects ("Blattopterans").[23] The dragonflies Odonata were the dominant aerial predator and probably dominated terrestrial insect predation as well. True Odonata appeared in the Permian[24][25] and all are amphibian. Their prototypes are the oldest winged fossils,[26] go back to the Devonian, and are different from other wings in every way.[27] Their prototypes may have had the beginnings of many modern attributes even by late Carboniferous and it is possible that they even captured small vertebrates, for some species had a wing span of 71 cm.[25] The oldest known insect that resembles species of Coleoptera date back to the Lower Permian (270 million years ago), though they instead have 13- segmented antennae, elytra with more fully developed venation and more irregular longitudinal ribbing, and an abdomen and ovipositor extending beyond the apex of the elytra. The oldest true beetle would have features that include 11-segmented antennae, regular longitudinal ribbing on the elytra, and having genitalia that are internal.[17] The earliest beetle-like species had pointed, leather like forewings with cells and pits. Hemiptera, or true bugs had appeared in the form of Arctiniscytina and Paraknightia. The later had expanded parapronotal lobes, a large ovipositor, and forewings with unusual venation, possibly diverging from Blattoptera. The orders Raphidioptera and Neuroptera are grouped together as Neuropterida. The one family of putative Raphidiopteran clade (Sojanoraphidiidae) has been controversially placed as so. Although the group had a long ovipositor distinctive to this order and a series of short crossveins, however with a primitive wing venation. Early families of Plecoptera had wing venation consistent with the order and its recent descendants.[9]:186 Psocoptera was first appeared in the Permian period, they are often regarded as the most primitive of the hemipteroids.[28] Triassic Page 10 of 39 Evolution of insects - Wikipedia 1/2/2017 https://en.wikipedia.org/wiki/Evolution_of_insects The Triassic (252 to 201 million years ago) was a period when arid and semiarid savannas developed and when the first mammals, dinosaurs, and pterosaurs also appeared. During the Triassic, almost all the Earth's land mass was still concentrated into Pangaea. From the east a vast gulf entered Pangaea, the Tethys sea. The remaining shores were surrounded by the world-ocean known as Panthalassa. The supercontinent Pangaea was rifting during the Triassic—especially late in the period—but had not yet separated.[17] The climate of the Triassic was generally hot and dry, forming typical red bed sandstones and evaporites. There is no evidence of glaciation at or near either pole; in fact, the polar regions were apparently moist and temperate, a climate suitable for reptile-like creatures. Pangaea's large size limited the moderating effect of the global ocean; its continental climate was highly seasonal, with very hot summers and cold winters. It probably had strong, cross-equatorial monsoons.[29] As a consequence of the P-Tr Mass Extinction at the border of Permian and Triassic, there is only little fossil record of insects including beetles from the Lower Triassic.[30] However, there are a few exemptions, like in Eastern Europe: At the Babiy Kamen site in the Kuznetsk Basin numerous beetle fossils were discovered, even entire specimen of the infraorders Archostemata (i.e., Ademosynidae, Schizocoleidae), Adephaga (i.e., Triaplidae, Trachypachidae) and Polyphaga (i.e., Hydrophilidae, Byrrhidae, Elateroidea) and in nearly a perfectly preserved condition.[31] However, species from the families Cupedidae and Schizophoroidae are not present at this site, whereas they dominate at other fossil sites from the Lower Triassic. Further records are known from Khey-Yaga, Russia in the Korotaikha Basin.[17] Around this time, during the Late Triassic, mycetophagous, or fungus feeding species of beetle (i.e., Cupedidae) appear in the fossil record. In the stages of the Upper Triassic representatives of the algophagous, or algae feeding species (i.e., Triaplidae and Hydrophilidae) begin to appear, as well as predatory water beetles. The first primitive weevils appear (i.e., Obrienidae), as well as the first representatives of the rove beetles (i.e., Staphylinidae), which show no marked difference in physique compared to recent species.[17] Page 11 of 39 Evolution of insects - Wikipedia 1/2/2017 https://en.wikipedia.org/wiki/Evolution_of_insects This was also around the first time evidence of diverse freshwater insect fauna appeared. Some of the oldest living families also appear around during the Triassic, including from Hemiptera: Cercopidae, Cicadellidae, Cixiidae, and Membracidae; from Coleoptera: Carabidae, Staphylinidae, and Trachypachidae; from Hymenoptera: Xyelidae; From Diptera: Anisopodidae, Chironomidae, and Tipulidae. The first flies (Diptera), Hymenoptera, and true dragonflies (Odonata), Heteroptera, and Thysanoptera. The first true species of Diptera are known from the Middle Triassic, becoming widespread during the Middle and Late Triassic . A single large wing from a species of Diptera in the Triassic (10 mm instead of usual 2–6 mm) was found in Australia (Mt. Crosby). This family Tilliardipteridae, despite of the numerous 'tipuloid' features, should be included in Psychodomorpha sensu Hennig on account of loss of the convex distal 1A reaching wing margin and formation of the anal loop.[32] Jurassic The Jurassic (201 to 145 million years ago) was important in the development of birds, one of the insects' major predators. During the early Jurassic period, the supercontinent Pangaea broke 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 Ocean was relatively narrow, while the South Atlantic did not open until the following Cretaceous Period, when Gondwana itself rifted apart.[33] The global climate during the Jurassic was warm and humid. Similar to the Triassic, there were no larger landmasses situated near the polar caps and consequently, no inland ice sheets existed during the Jurassic. Although some areas of North and South America and Africa stayed arid, large parts of the continental landmasses were lush. The laurasian and the gondwanian fauna differed considerably in the Early Jurassic. Later it became more intercontinental and many species started to spread globally.[17] Page 12 of 39 Evolution of insects - Wikipedia 1/2/2017 https://en.wikipedia.org/wiki/Evolution_of_insects There are many important sites from the Jurassic, with more than 150 important sites with beetle fossils, the majority being situated in Eastern Europe and North Asia. In North America and especially in South America and Africa the number of sites from that time period is smaller and the sites have not been exhaustively investigated yet. Outstanding fossil sites include Solnhofen in Upper Bavaria, Germany,[34] Karatau in South Kazakhstan,[35] the Yixian formation in Liaoning, North China[36] as well as the Jiulongshan formation and further fossil sites in Mongolia. In North America there are only a few sites with fossil records of insects from the Jurassic, namely the shell limestone deposits in the Hartford basin, the Deerfield basin and the Newark basin.[17][37] Numerous deposits of other insects occur in Europe and Asia. Including Grimmen and Solnhofen, German; Solnhofen being famous for findings of the earliest birds (i.e. Archaeopteryx). Others include Dorset, England; Issyk-Kul, Kirghizstan; and the most productive site of all, Karatau, Kazakhstan. During the Jurassic there was a dramatic increase in the known diversity of family-level Coleoptera.[17] This includes the development and growth of carnivorous and herbivorous species. Species of the superfamily Chrysomeloidea are believed to have developed around the same time, which include a wide array of plant host ranging from cycads and conifers, to angiosperms.[38]:186 Close to the Upper Jurassic, the portion of the Cupedidae decreased, however at the same time the diversity of the early plant eating, or phytophagous species increased. Most of the recent phytophagous species of Coleoptera feed on flowering plants or angiosperms. Cretaceous The Cretaceous (145 to 65 million years ago) had much of the same insect fauna as the Jurassic until much later on. During the Cretaceous, the late- Paleozoic-to-early-Mesozoic supercontinent of Pangaea completed its tectonic breakup into present day continents, although their positions were substantially different at the time. As the Atlantic Ocean widened, the convergent-margin orogenies that had begun during the Jurassic continued in Page 13 of 39 Evolution of insects - Wikipedia 1/2/2017 https://en.wikipedia.org/wiki/Evolution_of_insects the North American Cordillera, as the Nevadan orogeny was followed by the Sevier and Laramide orogenies. Though Gondwana was still intact in the beginning of the Cretaceous, it broke up as South America, Antarctica and Australia rifted away from Africa (though India and Madagascar remained attached to each other); thus, the South Atlantic and Indian Oceans were newly formed. Such active rifting lifted great undersea mountain chains along the welts, raising eustatic sea levels worldwide. To the north of Africa the Tethys Sea continued to narrow. Broad shallow seas advanced across central North America (the Western Interior Seaway) and Europe, then receded late in the period, leaving thick marine deposits sandwiched between coal beds. At the peak of the Cretaceous transgression, one-third of Earth's present land area was submerged.[39] The Berriasian epoch showed a cooling trend that had been seen in the last epoch of the Jurassic. There is evidence that snowfalls were common in the higher latitudes and the tropics became wetter than during the Triassic and Jurassic.[40] Glaciation was however restricted to alpine glaciers on some high-latitude mountains, though seasonal snow may have existed farther south. Rafting by ice of stones into marine environments occurred during much of the Cretaceous but evidence of deposition directly from glaciers is limited to the Early Cretaceous of the Eromanga Basin in southern Australia.[41][42] There are a large number of important fossil sites worldwide containing beetles from the Cretaceous. Most of them are located in Europe and Asia and belong to the temperate climate zone during the Cretaceous. A few of the fossil sites mentioned in the chapter Jurassic also shed some light on the early cretaceous beetle fauna (e.g. the Yixian formation in Liaoning, North China). [36] Further important sites from the Lower Cretaceous include the Crato Fossil Beds in the Araripe basin in the Ceará, North Brazil as well as overlying Santana formation, with the latter was situated near the paleoequator, or the position of the earth's equator in the geologic past as defined for a specific geologic period. In Spain there are important sites near Montsec and Las Hoyas. In Australia the Koonwarra fossil beds of the Korumburra group, South Gippsland, Victoria is noteworthy. Important fossil sites from the Upper Cretaceous are Kzyl-Dzhar in South Kazakhstan and Arkagala in Russia.[17] Page 14 of 39 Evolution of insects - Wikipedia 1/2/2017 https://en.wikipedia.org/wiki/Evolution_of_insects During the Cretaceous the diversity of Cupedidae and Archostemata decreased considerably. Predatory ground beetles (Carabidae) and rove beetles (Staphylinidae) began to distribute into different patterns: whereas the Carabidae predominantly occurred in the warm regions, the Staphylinidae and click beetles (Elateridae) preferred many areas with temperate climate. Likewise, predatory species of Cleroidea and Cucujoidea, hunted their prey under the bark of trees together with the jewel beetles (Buprestidae). The jewel beetles diversity increased rapidly during the Cretaceous, as they were the primary consumers of wood,[43] while longhorn beetles (Cerambycidae) were rather rare and their diversity increased only towards the end of the Upper Cretaceous.[17] The first coprophagous beetles have been recorded from the Upper Cretaceous,[44] and are believed to have lived on the excrement of herbivorous dinosaurs, however there is still a discussion, whether the beetles were always tied to mammals during its development.[45] Also, the first species with an adaption of both larvae and adults to the aquatic lifestyle are found. Whirligig beetles (Gyrinidae) were moderately diverse, although other early beetles (i.e., Dytiscidae) were less, with the most widespread being the species of Coptoclavidae, which preyed on aquatic fly larvae.[17] Paleogene The Paleogene (65 to 23 million years ago) comprises the first part of the Cenozoic, which during this time the continents assumed their modern shapes. The fragments of Gondwana (South America, Africa, India and Australia) began to drift northwards. The collision of India with the Eurasian landmass led to the folding and formation of the Himalayas. Similarly, the Alps were folded in Central Europe by the collision of the African plate with Europe. A land bridge between North America and South America did not yet exist. The Atlantic Ocean continued to widen during the Paleogene. In the North, the last land bridge between North America and Europe broke up during the Eocene. Climate during the Paleogene was warm and tropical as most time during the Mesozoic. The climate in the beginning was drier and cooler than in the preceding Cretaceous, but the temperature strongly increased during the Eocene and subtropical vegetation spread up to Greenland and Patagonia. The Page 15 of 39 Evolution of insects - Wikipedia 1/2/2017 https://en.wikipedia.org/wiki/Evolution_of_insects