BRITISH and German researchers say they have discovered the giant fossilised claw of an ancient sea scorpion that, in its heyday hundreds of millions of years ago, would have been 2.5m long. The find, in a quarry near the western German border town of Pruem, is the biggest specimen of arthropod ever found, they said in a study published by Biology Letters, a journal of Britain's Royal Society. "This is an amazing discovery,'' said Simon Braddy, from the Department of Earth Science at the University of Bristol in western England. "We have known for some time that the fossil record yields monster millipedes, super-sized scorpions, colossal cockroaches and jumbo dragonflies, but we never realised until now just how big some of these ancient creepy-crawlies were.'' The 46cm claw was wielded by a species of sea scorpion called Jaekelopterus rhenaniae that lived between 460 and 255 million years ago. Using the claw as a benchmark, the scientists believe its owner was between 2.33m and 2.59m long. Chelicerae - wand-like appendages used to grasp food and bring it to the beast's mandibles - would have added another 50cm. "This exceeds the previously recorded maximum body length of any arthropod by almost half a metre, the chelicerae not included,'' the study said. Despite their name, sea scorpions, known as eurypterids, were not true scorpions. Equipped with long, flat, jointed carapaces, they stalked warm shallow sea waters from around 500 million to 250 million years ago, eventually moving into in fresh water. Biologists delving into Earth's distant past are divided as to how some arthropods were able to develop into such monstrous size. Some suggest that they benefit from an oxygen-rich atmosphere, while others argue that they had to get bigger in order to keep up with the supersizing of their likely prey, the early armoured fish. "There is no simple single explanation,'' said Mr Braddy. "It is more likely that some ancient arthropods were big because there was little competition from the vertebrates, as we see today. If the amount of oxygen in the atmosphere suddenly increased, it doesn't mean all the bugs would get bigger.''