First Tool Users Were Sea Scorpions?

Charles Q. Choi
for National Geographic News
April 13, 2009

The first tool-users in the world may have been scorpion-like sea beasts. The extinct animals used other creatures' shells to help them breathe on land 500 million years ago, new research suggests.

Five years ago paleontologists found dozens of strange fossil tracks, each about four inches (ten centimeters) wide, in half-billion-year-old rocks exposed at a flagstone quarry in Wisconsin.

The marks appear to have been made by multi-legged creatures that had all dragged some weight on their left sides.

The tracks look like those made by modern-day hermit crabs, but the marks date back to some 300 million years before those crustaceans existed. (See a prehistoric time line.)

Based on the footprint patterns, researchers suggest the tracks were made by sea scorpions, critters that resembled "a cross between a scorpion and a horseshoe crab," said lead study author James Whitey Hagadorn of Amherst College.

(Related: "Giant Sea Scorpion Discovered; Was Bigger Than a Man.")

Sea scorpions—thought to be among the first marine animals to evolve for life on land—breathed underwater using gills on their tails.

The odd drag marks could have been from the coiled shells of snails or similar critters, which the ocean-dwelling scorpions stuffed their tails into so they could venture above water, the researchers suggest.

Humid air trapped inside the shells might have protected the sea scorpions' gills from drying out during brief forays into the open air—like reverse scuba gear.

"Instead of an aqualung, like you have with human divers, you have the reverse: an aerolung," Hagadorn said.

These early pioneers may have explored sandy tidal flats to graze on the mats of photosynthetic microbes that literally covered early Earth, the researchers say.

"If I were these creatures," Hagadorn said, "and I saw a whole bunch of microbial mats exposed in low tide, where there were no predators or competition from any other animals, it would be like a free buffet."

Findings appear in the April issue of the journal Geology.




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