Ancient sea scorpion was bigger than a human

A handout image released in London November 21, 2007 shows a sea scorpion, a creature living before the age of dinosaurs.

LONDON (Reuters) - Scientists have found the fossilised claw of a 2.5-metre (8-foot) sea scorpion, a nightmarish creature living before the age of dinosaurs.

The discovery of the 390-million-year-old specimen in a German quarry suggests prehistoric spiders, insects and crabs were much larger than previously thought, researchers at Bristol University said on Wednesday."This is an amazing discovery," said university researcher Simon Braddy.

"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 find was described by Braddy and colleagues in the journal Biology Letters.

The claw of the sea scorpion Jaekelopterus rhenaniae measured 46 centimetres (18 inches) long, indicating the creature was half a metre longer than previous estimates of the ancient arthropods.

Just why prehistoric arthropods -- creatures with external skeletons and segmented bodies -- grew so large is unclear. Some scientists believe they may have become giants because of the higher levels of oxygen in the atmosphere in the past.

Another theory is that they evolved in an "arms race" alongside their likely prey, the early armoured fish.