The claw belonged to a specimen of Jaekelopterus rhenaniae roughly 2.5 metres long according to estimates (Image: Braddy et al. Biology Letters) The sturdy giant claw is all that remains of the creature whose softer body parts did not survive the fossilisation process (Image: Braddy et al. Biology Letters)

The fossilised remains of a giant claw that once belonged to a sea scorpion roughly 2.5 metres long have been found in Germany.


Researchers say the monstrous creature is the largest arthropod ever known – over 30 centimetres bigger than the previous largest specimen of the same species.

Simon Braddy at the University of Bristol, UK, and colleagues examined the 46-centimetre-long claw, found in a quarry in western Germany, and believe it belonged to a sea scorpion species called Jaekelopterus rhenaniae that roamed the ocean floors some 390 million years ago.

Some palaeontologists believe that J. rhenaniae used its claws to reach out and grab passing animals, such as fish, to eat. “They were the top predators at the time,” says Paul Selden at the University of Kansas in Lawrence, Kansas, US.

Sturdy claws

The claws of these creatures remain long after the rest of their body has disintegrated. “The body segments are quite flimsy,” Braddy explains, but “the claws are sturdy, so they preserve better in the fossil record.” As a result, his team had to extrapolate the size of the sea scorpion that once owned the massive claw.

Experts typically extrapolate the size of sea scorpions based on measurements of the claw and body size of the few specimens that have survived intact. But Braddy suspects that this simple method might lead to an overestimate of body size.

According to such calculations, the claw his group found would have belonged to a sea scorpion measuring 2.6 metres long. Braddy prefers a more conservative estimate of just under 2.5 metres.

Size mystery

J. rhenaniae belongs to a category of animals known as arthropods, distinguished by traits such as a segmented body and an exoskeleton, which includes modern species such as spiders and horseshoe crabs.

Although long extinct, some palaeontologists believe J. rhenaniae gave rise to modern-day land scorpions. Others believe that it represents an evolutionary dead end.

Why the creature reached such huge proportions remains something of a mystery, however.

Elevated levels of oxygen in the atmosphere may have allowed some prehistoric animals to grow very large, but Braddy points out that oxygen levels during the period in question were not elevated much beyond current levels. A much more likely explanation, he says, is that the sea scorpions needed a competitive advantage over other animals, including other related arthropods.

Journal reference: Biology Letters (DOI: 10.1098/rsbl.2007.0491)