A giant fossilized claw discovered in Germany belonged to an ancient sea scorpion that wasmuch bigger than the average man, an international team of geologists and archaeologists reported Tuesday.

A computer-generated image shows a size comparison between a human and an ancient sea scorpion. ((University of Bristol/Associated Press))

The 46-centimetre-long claw was discovered by report co-author Markus Poschmann, from Germany, in a quarry near Pruem, a city about 200 kilometres east of Frankfurt.

The researchers said the scorpion lived between 460 and 255 million years ago and would have been among the top predators in its environment, feeding on early vertebrates and smaller arthropods. The report saidthe creature likely only lived in the water because with the construction of its body, "it is hardly imaginable how such a huge arthropod could effectively walk on land."

In a report in the Royal Society's journal Biology Letters, the team said the claw indicates that sea scorpion Jaekelopterus rhenania was almost 2.5 metres long, making it the largest arthropod — an animal with a segmented body, jointed limbs and a hard exoskeleton — ever found. In the report, the authors said the scorpion exceeds previous size records for arthropods by almost half a metre.

The fossil, found in a 390-million-year-old rock, suggests that spiders, insects, crabs and similar creatures were much larger in the past than previously thought, the researchers said.

This claw belonged to a giant sea scorpion, estimated to be 2.5 metres long. ((Markus Poschmann) )

"This is an amazing discovery. We have known for some time that the fossil record yields monster millipedes, super-sized scorpions, colossal cockroaches, and jumbo dragonflies, but we never realized, until now, just how big some of these ancient creepy-crawlies were," said co-author Dr. Simon Braddy from the University of Bristol.

Some geologists believe that the giant arthropod evolved due to high oxygen levels, while others argue that they evolved in an "arms race" alongside their prey, the early armoured fish.