What is the oldest arachnid?

The oldest known arachnid is Horseshoe crab, which dates back approximately 450 million years. However, in terms of fossilized evidence, the earliest definitive arachnids are from the Silurian period, around 430 million years ago, including ancient scorpions and Spiders. These early arachnids played a significant role in terrestrial ecosystems and have evolved into the diverse group we see today.