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How Bizarre

Sea scorpions slashed victims with swordlike tails

New fossil suggests the body part was used for fighting, swimming

By
11:00am, May 30, 2017
sea scorpion illustration

EN GARDE!  Ancient sea scorpions (one illustrated) may have used serrated, swordlike tails for swimming or as weaponry.

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Ancient sea scorpions were hacks.

Some of the marine creatures had a thin, serrated spine on the tip of their tail — and that tail was surprisingly flexible, based on a 430-million-year-old fossil found in Scotland. Slimonia acuminata may have had the range of motion to strike large predators and prey, researchers report online April 18 in American Naturalist.

Scientists had thought that the ancient animals largely used their tails for swimming, primarily flapping them up and down like today’s lobsters and shrimp do and, to a limited degree, side to side like a rudder. But the tail on the new, well-preserved fossil curls dramatically to the side — a flexibility not seen in other sea scorpion specimens.

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S. acuminata

That bendiness suggests a purpose beyond propulsion, say study authors W. Scott Persons, a paleontologist, and John Acorn, an entomologist, both at the University of Alberta in Canada. The tail could have twisted around horizontally to strike a victim or dispatch a foe with the pointy end, and the saw-edged weapon would have encountered little water resistance.

Sea scorpions may have even pinned down prey with their front limbs while delivering lethal blows with their tails. Because S. acuminata appears quite early in sea scorpion evolution, slicing and dicing may have been the norm early on for the ancient critters, the researchers write.

Citations

W.S. Persons and J. Acorn. A sea scorpion’s strike: new evidence of extreme lateral flexibility in the opisthosoma of eurypterids. The American Naturalist. Published online April 18, 2017. doi: 10.1086/691967.

Further Reading

M. Rosen. Earliest sea scorpion discovered in Iowa. Science News. Vol. 188, November 14, 2015, p. 5.

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