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Wednesday, December 29, 2010

Sea scorpions weren’t as mean as they looked

Looks can be deceiving in the animal world. Take an extinct group of creatures known as sea scorpions, which thrived from about 470 to 370 million years ago. These 2 1/2 meter long clawed arthropods apparently were a lot less tough than they looked.

Sea scorpion fossil (Mixopetrus kjaeri).

Credit: Ghedoghedo, June 2009

Sea scorpions, also known as eurypterids, were gigantic ancient arthropods. Despite their name, they did not have venomous stingers. However, with their huge spine-covered claws, they were long thought to be one of the top predators of the Paleozoic period. A closer look at the mechanical constraints on those claws tells a different story. Richard Laub, Victor Tollerton and Richard Berkof wrote in the Bulletin of the Buffalo Society of Natural Sciences that sea scorpions would have been able to exert no more than half the force needed to crush horseshoe crabs, a common prey item of that era. To make matters worse, the sea scorpions lacked the necessary joints to allow them to grasp prey.

Present day arthropods are often predators, so sea scorpions, which were the largest arthropods ever, were expected to be equally carnivorous. This new evidence suggests that despite their fearsome appearance, they may have been predominantly scavengers. Laub even entertains the possibility that the creatures may have been vegetarians.

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