A newly discovered fossil brain suggests that the ancestors of spiders and other arachnids originated in the ocean rather than on land as previously thought. The unusual arrangement of the brain’s features, similar to those found in modern spiders, points to a marine-dwelling ancient sea creature called Mollisonia symmetrica as an early ancestor of modern arachnids.
The study, published in Current Biology, analyzed the fossilized brain and central nervous system of M. symmetrica from the Burgess Shale formation. Researchers found that certain regions of its brain appear to be arranged in the opposite direction compared with those of other arthropods, a characteristic shared by spiders. This unique arrangement is exclusive to arachnid brains, suggesting that M. symmetrica was an early arachnid.
The findings indicate that arachnids evolved and diverged from horseshoe crabs earlier than previously believed. The researchers propose that the inverted setup of the arachnid brain allowed for greater computational speed and control over motor actions, enabling stealthy and swift hunting on land. This adaptability may have contributed to the evolution of insect wings, giving spiders a crucial advantage in catching prey.
The study’s lead author notes that the similarity between M. symmetrica’s brain and those of modern spiders raises questions about their common lineage or mere coincidence. Using computational analysis, researchers estimated that the Mollisonia lineage eventually evolved into the arachnid group, suggesting a possible link to the “most successful arthropodan predators.”
Source: https://www.livescience.com/animals/arachnids/backward-brain-of-ancient-sea-creature-hints-spider-ancestors-evolved-in-the-ocean