Researchers believe that these creatures owe their body structure to their ancestors, who, in a very strange way, learned to use their appendages.
It would seem that the ideal number of legs on Earth simply does not exist: people have two, dogs prefer to move around on four, insects use six, and their number can exceed 1,000 in a centipede. live science.
According to Thomas Hagen, an assistant professor of invertebrate paleontology at the State University of New York, the simplest answer to this question is that spiders have 8 legs because “their parents looked like that.” If we go through the history of eight-legged spiders 500 million years ago, we come to the lineage of chelicerates – a group of arthropods to which spiders belong. Fast forward another 41 million years and we find ourselves in the ocean, among the lobules – the ancestors of all arthropods.
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Note that by the name “lobopod” scientists mean a wide variety of species with fairly simple bodies. In fact, they were worm-like creatures with segmented bodies – at the same time, identical pairs of short legs were located on each segment, and this pattern was preserved along the entire length of the body. The evolution of the lobules led to the fact that they began to separate the legs and merge parts of the body. As a result, the first chelicerates seem to have combined their segments into two large parts – the abdomen and the head. It seems strange that the head retained its legs, while the belly, on the contrary, lost them, however, the researchers still do not understand why this happened.
Researchers still don’t know what made cheetahs stop on their eight legs, Higgin says, but scientists do know a lot about where their legs came from in the first place. According to evolutionary biologist and director of the Marine Biology Laboratory at the University of Chicago, Nipam Patel, the legs of spider ancestors are actually part of their mouth. The researchers note that all arthropod appendages, including legs, antennae, and even the mandibles (mandibles), can be easily traced back to a short appendage to the lobes of the legs.
If you look at a spider embryo, it’s easy to see that it looks just like an insect embryo, says Patel. Its legs grow only from its head – however, instead of using them as food, the spider prefers to move with its legs.
The researchers note that the reason spiders actually walk with facial appendages has its roots in the lobes and the original body structure of the cichlids. According to Heather Bruce, a researcher at the Marine Biological Laboratory, all the legs of the ancestors of spiders were initially similar, but over time the appendages became more and more different – some were used to capture food, others for perception or movement.
The researchers noticed that over time, the limbs of the ancestors of the spider lost their sensory abilities and turned to prey, the second pair of clawed legs turned into a group of gripping appendages – the pedipalps, and the next four legs remained as a group used for locomotion. At the same time, all the other members were lost.
previously to focus He wrote that scientists have discovered that some of the largest spiders in the world are very shy.
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