Afraid of bugs? Then this creature might make an appearance in your nightmares. The recently discovered giant sea scorpion, otherwise known as Jaekelopterus rhenaniae, is thought to have been 8 feet tall. It lived about 400 million years ago. Experts say the giant sea scorpion may have evolved to such a large size in an "evolutionary arms race" with armored fish. Some experts say this long-extinct creature was a predecessor to modern-day land scorpions.