Last time, it was said that the arachnids were extinct at the beginning of the Permian. After the article was issued, many of my friends commented on the reasons. Everyone expressed their opinions. The well frog was greatly inspired and very grateful. To sum up the views of everyone here, it is: This is likely to be a total astronomical, fundamental, and structural flaw in the arachnid, and even the sacred arm.
The Permian is a historical node in the overall retreat of the cheeks and the general rise of the pan-shells. It is the arachnid (the ancient and the horned) and the extremity (the amphibians), and the pan-carapace (the aquatic crustaceans and the terrestrial hexapods) became the mainstay of arthropods until Today, 300 million people are prosperous. Image from , slightly modified.
The scabbards are likely to have originated in the Cambrian large appendages (see the fifty-first back iron shovel 0: tentacles? No! I want to chelate). In the Ordovician, the real cheeks appeared, and the basic body configuration of these animals was also determined: the body was divided into two parts: the head and the chest, and the head and chest were healed by 8 individual sections. limb. The first pair is the Chelicerae, which corresponds to the antennae of the polypod and the pan-carapace; the second pair is the Pedipalp, for example, the pair of large pliers is a specialized limb. Then there are 4 pairs of walking feet.
The spider avoids the appearance of two horrible big mouths, in fact it is a pair of cheeks. The source of the picture is the watermark.
The cheeks are not the most conspicuous pair of big pliers (that is the second pair of appendages: the limbs), but the pair of small pliers on the mouth in the picture above, it is hard to notice without careful observation. The image is from the web.
Above: whipping (with whip); middle picture: whip spider (no whip); lower picture: quasi-蝎 (preferential). They also evolve powerful limbs to capture prey. Look closely, in front of the limbs, there is a pair of short cheeks hidden under the head breast. The image is from the web.
This basic configuration was very advanced when it first appeared, taking into account sports, hunting and eating. After catching the prey, the arachnid will hold it to the mouth, crush it with a cheek, and suck the body fluid of the prey with its mouth.
In addition to the arachnid and the real eye, the chewing limbs of the major groups of the extremities are basically small pliers. Their function is to squeeze the prey, liquefy the flesh and blood, and suck it for the mouth. Image from .
However, in the Carboniferous, insects and terrestrial quadrupeds developed rapidly. Whether it is the insect's mouthparts or the quadruped's double-toothed teeth, the food range and feeding efficiency far exceed the arachnid chelation. At the same time, because the basic configuration is locked, the arachnid has no more head appendages to evolve into mouthparts (big cockroaches, small cockroaches and lips), which is an evolutionary knot.
Myriapod pan and crustaceans at least one pair of antennae responsible senses, additionally reserves the at least three pairs of appendages formed mouthpiece, the cutting is completed, chewing, swallowing movements. In contrast, chelicerata feeding apparatus is too shabby. Image from .
Plus no compound eyes and no antennae, feeling insensitive, fast enough, can not fly, can only be hunted live animals, eating slower, vulnerable to attack. Therefore, the basic structure of the arachnid is not suitable for hunting. When the earliest landing bonus is exhausted, the ancient spider and the horn spider are likely to become victims of survival competition.
Those that survived into modern and ancient hunting migratory taxa (Scorpiones, solifugae, thelyphonida, no whip mesh), very few species, and are mostly located on the edge of the Gobi desert habitat class of, also on the card side This survival mode is not suitable.
The number and proportion of existing arachnids summarized by the frog. The mites are far more than the other groups except spiders, especially those of the large and medium safari type (except for arachnids).
A scorpion is a large group of multiple lines. Their bodies are extremely specialized, but they still follow the basic structure of the arachnid. The cheeks and limbs are squeezed at the front of the body to form a sharp hollow straw that is used to absorb tissue or cell fluid from animals and plants. This avoids the positive competition with insects and quadrupeds. The source of the picture is the watermark.
Fortunately, the spider eye holds up half of the arachnid, and is the most important one. Why is it in a decline in the contrarian rise it? Probably because of mastering two big killers: fangs and spider silk. Make up said earlier, historic, fundamental to the maximum extent of structural defects.
If you remove the species proportion Araneae, arachnids of each group. Thanks Araneae keep up appearances, or iron scorpion wrote last hideous left with all kinds of itch itch (see one hundred and sixty eighth back iron scorpion hideous 11: itch) a.
Spider's fangs are deformed cheeks, unlike small pliers, like a folding knife. This knife-shaped corner terror spider chelicerae there (see the two hundred and twelfth back iron scorpion hideous 12: Early Permian mass extinction event), but the only venomous spiders (and possibly Ural spider) of chelicerae The venom can be injected into the body of the prey.
The chelation structure of the early Permian Ural spider Permarachne novokshonovi found in the Kungur region of Russia . Image from .
Permarachne novokshonovi fossils and structural drawings. The Ural and the ancient spiders are very similar. The biggest difference is that there is a long tail whip at the end of the abdomen. Image taken from  with a ruler length of 1 mm.
The most primitive spiders in existence: the chewing limbs of Liphistius bicoloripes , Mesothelae (also known as the subfamily or the subspecies) . The shape is very similar to the chelation of the Ural spider, but there are traces of venom gland (vg). Image courtesy of .
People used to think that the ancient scorpion was too primitive and had not evolved the venom gland. But new research shows that they are toxic glands, but degraded to varying degrees. Pictured above is a magnified photograph of the tip of Liphistius bristowei , where the opening of the venom is observed. Image courtesy of .
The appearance of the existing Liphistiidae, the subsection of the abdomen is the most prominent feature. Other more evolved spider abdomen has completely healed into one. The image is from the web.
The appearance of venom greatly compensates for the lack of eating methods: not only can kill prey in an instant, but also can quickly decompose the body of liquefied prey, the efficiency is improved, and it is safer.
As for the spider silk, that is a more remarkable evolutionary achievement. It can be said that in the future, the spiders will suddenly rise to the glory, relying on this hand, or the ability of this ass spinning net. Why do you say a bit? Because the spinning organ (spinner) grows behind the buttocks.
The ventral structure of three major groups of arachnids, A: ancient mites; B: primary mites; C: new mites. In the red frame at the back of the abdomen are the spinners, which are specialized appendages used to create complex spider web structures. The image is from the web.
The appearance of spider silk is much earlier than that of spiders. The researchers found the earliest spinning organ in the Devonian Ural spider Attercopus fimbriunguis , which is 80 million years from the real spider.
The fossil of the early Devonian Ural spider Attercopus fimbriunguis discovered in Gilboa, New York . In the figure A, there are rows of silk tubes in the red circle. Image taken from  with a ruler length of 0.5 mm.
From Attercopus fimbriunguis isolated on fossil fine organization. A: single wire tube (Spinneret); B: femur of the limbs; C: a skin with a silk tube, there seems to be traces of spider silk (D); E: base of the tail whip; F: fold Knife-like chewing. Image from .
People have always thought that the Ural spider and the ancient typhoon, like the horned spider, were extinct in the Permian. However, in 2018, the researchers discovered a "long tail spider" in the Cretaceous amber of Myanmar, named Chimerarachne yingi . [About the Chimera spider, the well frog has a related answerWhat is the significance of the "King's Chimera" discovered by the Southern Institute of Chinese Academy of Sciences to study the origin of spiders?
Amber fossil and restoration map of the Chimera spider. Its body and spinning machine, which is very similar to the ancient genus, the tail whip of the Ural spider, and the age of existence, are all telling the secrets of the unknown history of arachnids. Image from .
A modern ancient cockroach spider Ryuthela nishihirai . Its spinner (marked by s in Figure b) is very similar to the Chimera spider. Image from .
Possible evolutionary relationships between the genus Chimera and other groups of arachnids. At present, it tends to think that it is closer to the spider's purpose than the Ural. Image courtesy of .
The real spiders appeared in the late Carboniferous, all belonging to the ancient scorpion, with a small number of fossils. Fortunately, the spiders of the ancient Shuya have survived to this day, and people have a glimpse into the lifestyle of these ancient animals.
The crypt of two types of modern ancient spiders. Upper: Arachnid, no cover, signal line; Bottom: Seven-spindle family, with cover, no signal line. Image from .
The fossil of the Late Carboniferous scorpion spider Palaeothele montceauensis found in the Montceau-les-Mines, France . It is the earliest known spider. Image courtesy of .
Another arachnid Idmonarachne brasieri fossil and restoration map discovered by Monkavrell . It has a morphological structure very similar to that of a spider, but no traces of the venom gland and the spinner are found. It is likely to represent a branch that is very close to the spider's kinship, but to a different evolutionary route. Image courtesy of .
The Late Carboniferous ancient spider Spider Arthrolycosa sp. fossil discovered in the Tunguska Basin, Russia . Image taken from  with a ruler length of 1 mm.
The appearance of the spider silk changed the survival pattern of the Ural spiders and early spiders. They gave up the safari life that they were not good at, and dig the caves on the surface of the soil to reinforce the cave walls with spider silk. The spider silk that extends to the outside of the cave can collect a variety of tiny vibrations, amplify it, and transmit it to the receptors in the foot, thereby distinguishing whether it is a prey or a natural enemy, making up for the innate deficiency of the senses. After catching the prey, you can enjoy it in the crypt. And later it turned out that when the disaster hit, the small animals that burrowed were often the highest survivors.
When the two waves of extinction at the end of the Permian and the end of the Triassic finally settled, the surviving spiders climbed out of the crypt, and the ability to spit the net became brilliant, and the prey of the bottom groundwater in the sky was collected. That is another long story.
The evolutionary relationship spectrum of existing spiders. They are the most successful terrestrial arthropods except insects. Image courtesy of .
Earth business card
Taxonomy: Animals - Arthropods - Chewings - Arachnids - Arachnids - Ancient Orders
Existence time: Late Carboniferous to Modern
Existing species: about 116 species
Fossil species: very few
Living environment: land
Representative features: abdominal segment, venom gland degeneration, the spindle is located in the middle of the abdomen
Representative group: belly spider, seven spinning spider
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