First scorpions may have crawled from the seas

D. Rudkin/Royal Ontario Museum

First scorpions may have crawled from the seas

The origins of scorpions are murky. The oldest of these arachnids (a group that also includes modern-day spiders, ticks, and mites) are known from fossils from Scottish rocks laid down between 433 million and 438 million years ago that show only their outlines. Now, well-preserved but slightly younger fossils from southwestern Ontario suggest that the animals originated in the seas—and may have been able to clamber onto shore well before the time scientists previously recognized. Those fossils—11 specimens in all—were entombed in sediments laid down on the shores of ancient lagoons between 430 million and 433 million years ago. And because all of them are of molted exoskeletons and not carcasses, the remains were too fragile to be washed to their final resting place from somewhere else, researchers suggest. Thus, the remains were probably shed at the water’s edge and preserved there, the team reports online today in the Proceedings of the Royal Society B. Anatomical traits of the new species back up that notion: The creature apparently didn’t have feeding structures enabling life on land. Yet the last segment of its legs was relatively short, allowing it to plant its “foot” flat, like modern-day scorpions, instead of walking on tiptoe like other water-dwelling scorpions of the era were presumed to do. The scorpion’s ability to fully support its own weight when out of water (and therefore escape solely aquatic predators) would have been a tremendous evolutionary benefit, the researchers note: As is the case with their modern-day kin, when the scorpions molted they would have been extremely vulnerable.

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