Claws for thought

Abstract

There is striking fossil evidence that much larger arthropods once existed on the planet, but a new find pushes the boundaries even further. From the sediments in a German quarry a giant claw has been recovered, whose owner was a sea scorpion. The size of the claw suggests that the organism possessing it had a body length of up to 2.5 metres. Simon Braddy, at the University of Bristol, Markus Poschmann of the Archaeological Service in Mainz and O. Erik Tetlie at Yale University, report the find in Biology Letters of the Royal Society (published online), and suggest it came from the largest ever arthropod ever recorded. The claw was found by Markus Poschmann in rocks 390 million years old in a quarry near Pruen. “I was loosening pieces of rock with a hammer and chisel when I suddenly realised there was a dark patch of organic matter on a freshly removed slab. After some cleaning I could identify this as a small part of a large claw.” Late Palaeozoic arthropod groups evolved gigantic representatives generally attributed to a higher atmospheric oxygen concentration of 35 per cent compared with 21 per cent today. Researchers have looked at a number of factors that may have allowed arthropods to reach such sizes, and constrained them under present conditions. The ability of the tracheae to transport oxygen to the tissues has been a subject of particular interest (see Curr. Biol. 17, R969–R971). But for this giant sea scorpion, the authors believe other mechanisms may have been involved, perhaps an ‘arms race’ with other competing predators.