Oldest Known Scorpion Fossil May Be One Of The First Animals To Explore Land

The fossil (left) was unearthed in Wisconsin in 1985. Scientists analyzed it and discovered the ancient animal's respiratory and circulatory organs (center) were near-identical to those of a modern-day scorpion (right). Andrew Wendruff

Scientists have discovered the oldest known fossil of a scorpion – thought to be some of the first animals to leave the oceans and explore land – dating back to around 437 million years ago. Reported in the journal Scientific Reports, the “groundbreaking discovery” could shed some much-needed light on how the first animals made the momentous transition out of the sea to become land-dwelling creatures. 

The fossil was first discovered in the 1980s around the outskirts of Waukesha in Wisconsin, USA. With scientists unaware of its significance, the specimen was stowed away in a dusty museum for over 30 years until it was recently reexamined by researchers from Ohio State University and Otterbein University.

The scorpion, recently dubbed Parioscorpio venator, is about 2.5 centimeters (1 inch) long, a similar size to many scorpions alive today. The layer of rock it was found in dates to between 436.5 and 437.5 million years ago, during the early part of the Silurian period, a time when Wisconsin was covered in a warm and shallow sea. 

Most importantly, the scorpion was found to have respiratory and circulatory systems that are almost identical to those of our modern-day scorpions (as seen in the image above). This suggests that the ancient scorpion’s respiratory system most likely behaved like a modern-day horseshoe crab, allowing it to spend prolonged periods on land, despite spending most of its time in the water. 

“It's a groundbreaking discovery," Loren Babcock, study author and a professor of earth sciences at Ohio State University, said in a statement.

“The inner workings of the respiratory-circulatory system in this animal are, shape-wise, identical to those of the arachnids and scorpions that breathe air exclusively,” Babcock added. “But it also is incredibly similar to what we recognize in marine arthropods like horseshoe crabs. So, it looks like this scorpion, this lineage, must have been pre-adapted to life on land, meaning they had the morphologic capability to make that transition, even before they first stepped onto land.”

The earliest known scorpion before this discovery was found in Scotland and dated to about 434 million years ago. This new fossil, at least 2.5 million years its senior, provides the oldest and some of the clearest evidence of animals that became capable of exploring the land. In turn, this could perhaps explain how our own vertebrate ancient ancestors made this all-important leap from sea to land.

"We're looking at the oldest known scorpion – the oldest known member of the arachnid lineage, which has been one of the most successful land-going creatures in all of Earth history," continued Babcock. 

"And beyond that, what is of even greater significance is that we've identified a mechanism by which animals made that critical transition from a marine habitat to a terrestrial habitat. It provides a model for other kinds of animals that have made that transition including, potentially, vertebrate animals.”

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