Spiders, scorpions and their relatives are among the most successful carnivorous invertebrates. The origin of these arachnids has so far been suspected in the country. Now paleontologists have discovered the fossil of an early arachnetic ancestor from the Cambrium, which refutes this assumption. Accordingly, the Arachnids’ ancestors could have developed in the sea before their descendants then conquered the country. For this, the nervous system of the fossil obtained speaks, which has astonishing parallels to the modern arachnid.
Spiders, scorpions, mites and their relatives have existed for over 400 million. These animals belonging to the class of arachnids – arachnids – today colonize a variety of habitats and have hardly changed their basic body structure over millions of years. However, while some representatives of the chelicerates, including the arrow tail crabs, are living in the sea, the arachnids are primarily lived in the sea. Only a few species have subsequently adapted to life in the water. On the basis of previous fossil finds and family tree reconstructions, researchers therefore assumed that the arachnid only developed from water to the country after the transition of their chelicerate ancestors – similar to insects and thousands of thousands.
A fossil brain with a surprise
But that could have been a mistake, as it is now clear. Researchers around Nichola’s Strausfeld from the University of Arizona have re -analyzed the fossil of an early species, which is considered the possible ancestor of the arachnid. The animal, Mollisonia Symmetrica, lived around 500 million years ago on the seabed of the Cambrium and was only a few centimeters tall. So far, Mollisonia has been considered a member of the Chelicerate, but not yet a penalty. With the help of modern analysis methods, Strausfeld and his team managed to take a more detailed view of the inner structures of this primeval seafare for the first time. It turned out that Mollisonia had a nervous system typical of arachnids in the front body section, which was connected to five pairs of legs. The brain was unsettled and had short, zangte -like nerve processes that are reminiscent of the jaw claws of modern spiders.
The most surprising feature, however, was the structure of the brain that was still recognizable in the petrification. Just like in today’s arachnids, it was built up and mirror image of that of arrow tail crabs, crustaceans and insects. The brain of this primeval choralate was actually far too modern for its time, as the researchers report. They therefore suspect that Mollisonia was not an early chelicer advantages of the arachnids, but possibly already belonged to a sister group of the modern Arachnids. This also turns on the previously suspected origin of the arachnids on the head. “Our study suggests that they were originally marine animals that later adapted to life on land,” explains Strausfeld. So the arachnids may not have been created on land as previously.
Efficient interconnection as a recipe for success
This finding also throws new light on the peculiarities of the spider animal brain and its role in hunting. “The brain of the arachnids is different from any other on this planet,” explains Strausfeld. The typical, “converted” organization of the brain, which is typical of spiders and their relatives, presumably shortens the paths between sensory and motor nerve centers, which enables lightning -fast reactions and finely coordinated movements. Spiders owe this neuronal efficiency to their high hunting speed and its skill in network construction. The fact that this special interconnection was already available at Mollisonia suggests that the evolutionary foundation for the hunting success of the arachnids has already been laid in the sea.
Later the descendants of these pioneers also conquered the country – and found a rich buffet on early insects and thousand feet. This could even contribute to the development of a decisive defense mechanism: the insect wing. Strausfeld speculates that the threat caused by early Arachnids increased the evolutionary pressure on other animals – and thus also promoted the development of escape strategies. “The ability to fly gives a significant advantage if you are persecuted by a spider,” he says.
Source: Nicholas Strausfeld (University of Arizona) et al.; Current biology, DOI: 10.1016/J.CUB.2025.06.063
