Ancient Giant "Bug" Discovered

Buried in 390-million-year-old rocks, scientists have recently discovered the claw to an extinct Eurypterid (sea scorpion), Jaekelopterus rhananine. With the possible exception of the Arthropleura, this is the largest arthropod ever discovered. As reported by the Royal Society, the complete animal was about 2.5 metres long (a little over 8 feet).

Why these creatures grew to such lengths, no one is sure. Two possible explanations: greater amounts of oxygen in the atmosphere and a lack of predation. A correlation between the increase of carbon dioxide and (predatory) jawed fishes and the extinction of the Eurypterids?