A trio of paleontologists has announced the discovery of a fossil belonging to a new species of ancient arthropod that rivals the largest ever found. They detail their finding in Wednesday's publication of the journal Nature. Hundreds of millions of years ago, arthropods, which include modern-day spiders, insects, and crustaceans, were much larger, and we're not talking the size of a small dog. An extinct millipede called Arthropleura reached up to 8.5 feet in length, making it the largest land invertebrate ever known to exist. Jaekelopterus rhenaniae, which extended 8.2 feet, dwelled in the water (pictured right).