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07.08.2016 23:23 - A Complete Encyclopedia Of The Largest Prehistoric Animals Vol.2 Invertebrates Part 2 Arthropods Ch.1 Chelicerata - Arachnids, Scorpiones and Spiders
Автор: valentint Категория: Политика   
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Scorpiones
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1. Pulmonoscorpius 2. Palaeoscorpius 3. Brontoscorpio 4. Anthracoscorpio 5. Proscorpius
Scorpions are the oldest arachnids for which fossils are known, and they were the first arachnid fossils to be found in Paleozoic strata. The Silurian scorpions appear to have lived in the water, since their fossils have gills, but by the Carboniferous scorpions with such features are no longer found -- fossils from the Pennsylvanian age Mazon Creek beds have book lungs covered by protective plates, and so were probably land-dwellers. The best scorpion fossils come from the Devonian and the Oligocene; there is a severe lack of fossils known from the intervening period.
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These earliest scorpiones are considered to be Protoscorpions, since they possess many traits which are plesiomorphic for scorpions. For example, in all scorpions the thick front portion on the abdomen is made up of seven segments, but the number of sternite plates which cover this region varies among the earliest fossils, while all living species have five. All scorpions have an additional five segments after the initial seven, ending in a sharp sting. This sting contains a pair of poison glands which can paralyze prey, usually insects or small rodents, or may deliver a painful sting to incautious persons. Most scorpion stings are merely painful, leading to swelling in the immediate region of the sting, but some scorpions of northern Africa and the American southwest can be deadly. In the US, the deadliest scorpions are to be found in Arizona, where it is a good idea to shake out shoes before putting them on in the morning!
Besides their unusually long and dangerous tails, scorpions also differ from other arachnids in having large pedipalps. These are the second pair of appendages on the body, and are usually rather inconspicuous in arachnids, but in scorpions, they are large and powerful pincers which may be used to grasp and subdue prey. Scorpions may also have more eyes than other arachnids, some species possessing as many as six pairs, though most do not have this many. They have three joints in their chelicerae, or the first pair of appendages, located next to the mouth.
Most scorpions are nocturnal, hiding under rocks, in crevices, or within burrows during the day, and coming out after sunset. Because of this, and because of their painful stings, it can be dangerous to travel at night in scorpion territory without shoes, even inside homes. (I have nearly stepped on a scorpion in my parents" home near Dallas.) One unusual feature of scorpions that has helped many field biologists is the UV fluorescence of scorpion bodies. Biologists hunting for scorpions wave an ultraviolet light near the ground as they walk along, watching for an eerie greenish light to be reflected back. The UV light is absorbed by the scorpion"s armor and is reflected back as visible light.


Brontoscorpio anglicus

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1. Stylonurus powriensis 2. Brontoscorpio anglicus 3. Pulmonoscorpius kriktonensis

Brontoscorpio anglicus ("English thunder scorpion") was a 1-metre long aquatic scorpion that lived during the Silurian period. When alive, B. anglicus would have resembled an oversized scorpion, albeit with relatively large (for a scorpion) compound eyes; it was an important predator of its time, given that the arthropods were among the largest animals on Earth during the Silurian.
All post-Paleozoic scorpions are terrestrial, while during the Silurian many of the known taxa made the transition from aquatic to terrestrial environments. It has been inferred that Brontoscorpio was capable of leaving the water and entering land, whether to evade other predators, such as large nautiloids, eurypterids, or even other aquatic scorpions; or pursue prey, such as other, smaller terrestrial scorpions. However, given its great size, B. anglicus had to return to the water when it tired of supporting its own weight, or at the very least whenever it moulted its exoskeleton (on land, it would risk being crushed by its own mass)[citation needed]. Marine scorpions such as B. anglicus captured, stung, and ate small sea animals such as fish like acanthodians, heterostracans, smaller scorpions and trilobites.
As with other arachnids, such as modern scorpions, Brontoscorpio respired through gas exchange via pores in its exoskeleton and the inner linings of its book lungs. Its tail was tipped with a large, venomous stinger that was, according to Walking with Monsters, the size of a light bulb.


Pulmonoscorpius kirktonensis
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Pulmonoscorpius kirktonensis (literally breathing scorpion) is a giant species of extinct scorpion that lived during the Visйan epoch of the Carboniferous. Its fossils were found at East Kirkton, West Lothian in Scotland. In life, this species grew to 70 centimetres (28 in) and even over a
1meter (40 in) in length.
Like the giant Meganeura, Pulmonoscorpius is thought to have achieved its large size from the higher oxygen content of the air of the Carboniferous period. The superficial morphology of Pulmonoscorpius is that of a larger version to today’s scorpions, although its proportionally larger eyes have led to the suggestion that it may have been a more visually orientated hunter.
It is impossible to say how toxic the venom of Pulmonoscorpius would have been, but a good rule of thumb is that the smaller the pincers are in relation to the thickness of the tail, the more potent the venom, with the thicker tails holding larger amounts.This holds true to today’s scorpions with those that have small pincers and fat tails being more feared by people who have become accustomed to their presence.
It is also hard to say with certainty what the diet of Pulmonoscorpius would have been, although as a scorpion it would almost certainly have been carnivorous. It may have focused its attentions upon other large arthropods, and maybe even the smaller amphibians and early reptiles. One clue may be the relatively small size of the pincers, indicating either a focus on prey smaller than itself, or a greater reliance on its venom to take down larger prey which was then manipulated with the pincers when dead.


Spiders
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1. Eodiplurina 2. Cretamygale 3. Friularachne 4. Electrocteniza
The evolution of spiders has been going on for at least 380 million years, since the first true spiders (thin-waisted arachnids) 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 (see External links for most recent list of fossil species). 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, and walking on eight legs, with a pair of leg-like pedipalps near the mouth and mouth parts. Arguments still remain open as to whether they possessed the ability to create silk. 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.
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1. Maiocercus 2. Palaeocharinus 3. Kreischeria 4. Eophrynus 5. Aphantomartus
Trigonotarbids are not true spiders, and most Trigonotarbid species have no living descendants today. One lineage, however, led eventually to the earliest tetrapulmonates, which then evolved into spiders, whip scorpions, and 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 the Carboniferous age, or about 300 million years ago. Most of these early segmented fossil spiders from the Coal Measures of Europe and North America probably belonged to the Mesothelae, or something very 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 probably ground-dwelling predators, living in the giant clubmoss and fern forests of the mid-late Palaeozoic, where they were presumably predators of other primitive arthropods. Silk may have been used simply as a protective covering for the eggs, a lining for a retreat hole, and later perhaps for simple ground sheet web and trapdoor construction.
As plant and insect life diversified so also did the spider"s use of silk. Spiders with spinnerets at the end of the abdomen (Mygalomorphae and Araneomorphae) appeared more than 250 million years ago, presumably 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.
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1. Dinopilio 2. Arthromygale 3. Arthrolycosa  4. Geralycosa
The oldest mygalomorph, Rosamygale, 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 (34 cm) and leg span of above 20 inches (50 cm), the largest known spider ever to have lived on Earth, but subsequent examination by an expert revealed that it was actually a relatively small sea scorpion.
By the Jurassic, the sophisticated aerial webs of the orb-weaver spiders had already developed to take advantage of the rapidly 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 of a spider.
The 110-million-year-old amber-preserved web is also the oldest to show trapped insects, containing a beetle, a mite, a wasp"s leg, and a fly.The ability to weave orb webs is thought to have been "lost", and sometimes even re-evolved or evolved separately, in different breeds of spiders since its first appearance.

NOTE!!! In modern pop culture and nightmares of men is full of giant spiders.For many people they come from prehistoric times,when everything was greater than now.The truth is that the biggest spiders now live alongside us.The biggest prehistoric spider was Mongolarachne. Female total body length estimated at 24.6 millimeters long, with forwards length 56.5 millimetres long. Male total body length 16.54 millimetres long. For comparison the largest species of arachnid by length is probably the giant huntsman spider (Heteropoda maxima) of Laos, which in 2008 replaced the Goliath birdeater (Theraphosa blondi) of northern South America as the largest known spider by leg-span.However the most massive arachnids, of comparable dimensions and possibly even greater mass, are the Chaco golden knee, Grammostola pulchripes, and the Brazilian salmon pink, Lasiodora parahybana. The huntsman spider may span up to 29 cm (11 in) across the legs, while in the New World "tarantulas" like Theraphosa can range up to 26 cm (10 in).In Grammostola, Theraphosa and Lasiodora, the weight is projected to be up to at least 150 g (5.3 oz) and body length is up to 10 cm (3.9 in).


Megarachne
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Megarachne servinei was originally described in 1980 by the Argentinean palaeontologist Mario Hьnicken. The holotype was recovered from the Pallero Member of the Bajo de Vйliz Formation of Argentina, a locality dated to the Asselian Age (298.9 ± 0.2 to 295.5 ± 0.4 million years ago (Ma)).Hьnicken wrongly identified the specimen as a mygalomorph spider based on the shape of the carapace, the 15 millimetres (0.59 in) wide circular eye tubercle located between the two eyes in the center of the head, a structure in front of the carapace he identified as spatulate chelicerae, and a circular structure behind the first body segment which he identified as the "moderately hairy" abdomen. Hьnicken"s identification relied heavily on X-ray microtomography of the holotype, and additional hidden structures were also extrapolated from the X-radiographs.
With a legspan estimated to be 50 centimetres (20 in), this would have made Megarachne servinei the largest spider to have ever existed, far exceeding the goliath birdeater (Theraphosa leblondi) which has a maximum legspan of only around 30 centimetres (12 in). The discovery quickly became popular and various exhibits with reconstructions of Megarachne servinei as a gigantic spider were set up in museums around the world.
The identification of the specimen as a spider was doubted by some arachnologists. Even Hьnicken himself acknowledged discrepancies in the morphology of the fossil that could not be accommodated with an arachnid identity. However, the holotype was by then deposited in a bank vault and other paleontologists had access only to the plaster casts.






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Автор: valentint
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