Early Scorpions May Have Transitioned To Land Earlier Than Thought

David Rudkin, Royal Ontario Museum

Scorpions have been crawling around our planet for hundreds of millions of years, and while it’s thought that the earliest versions were sea dwellers, when they first made the transition from water to land is hazy. Now, with the discovery of a previously unknown species with a unique combination of features, scientists have evidence to suggest that they scurried out of our oceans much earlier than originally believed.

The new species, Eramoscorpius brucensis, was identified from a total of 11 specimens from the Bruce Peninsula, Ontario, some of which first turned up in people’s backyards. The specimens, which ranged in length from 29 millimeters (1.1 inches) to 165 millimeters (6.5 inches), were preserved in layers of sediments deposited on the shores of ancient lagoons some 430 to 433 million years ago. This makes them slightly younger than the oldest known scorpion fossils, which were embedded in 433-to-438-million-year-old rock from Scotland.

Unlike E. brucensis, these ancient scorpions had stubby, pointed “crab-like” legs, which meant they would have walked on their “toes,” much like how modern day crabs scurry along the sand. Because these species are known from specimens encased within rocks that were originally deposited in the ocean, scientists generally agree that these animals probably evolved on the seafloor before eventually leaving their watery home in favor of a terrestrial life.

When precisely this event occurred has been somewhat of a mystery, but E. brucensis is giving scientists an idea. Although the species didn’t possess structures, called coxapophyses, which enable feeding on land, the animal did have a strange pair of legs that hinted it could at least walk on terrestrial surfaces.

As described in Proceedings of the Royal Society B, the last segment of its legs was relatively short, meaning that it could have set its tarsus (foot) flat against the ground, much like how modern-day scorpions walk. According to study author Janet Waddington, this means that the animals were able to support their own weight and therefore didn’t require water to buoy them up.

So if these animals could indeed walk on land, why were they found in marine rocks? As pointed out by Live Science, the answer likely lies within the researchers’ suspicion that the specimens are not actually the fossilized remains of scorpion bodies, but instead molted exoskeletons. Because animals are immobile during the molting process, they are extremely vulnerable to being gobbled up by marine predators. Animals that could escape the sea and take refuge on land or along the shore would therefore have had an advantage.

According to the researchers, these findings seem to indicate that scorpions began developing adaptations for terrestrial life much earlier than previously believed.

[Via Live Science, Science and Proceedings of the Royal Society B

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