The exceptionally preserved fossils of the oldest species of scorpion ever found have been unearthed in Wisconsin, the United States.
The newly-discovered ancient scorpion lived around 437 million years ago during the early Silurian period.
Dubbed Parioscorpio venator, the animal was about 2.5 cm (one inch) long — about the same size as many extant scorpions.
The creature is the earliest scorpion yet reported, and it provides new information about how animals transitioned from living in the sea to living entirely on land.
Its respiratory and circulatory systems are almost identical to those of extant scorpions and operate similarly to those of a horseshoe crab.
“Parioscorpio venator shows a crucial evolutionary link between the way ancient ancestors of scorpions respired under water, and the way modern-day scorpions breathe on land,” said Professor Loren Babcock, a paleontologist in the School of Earth Sciences at the Ohio State University.
“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,” he explained.
“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 fossilized remains of Parioscorpio venator were unearthed in 1985 from the Brandon Bridge Formation, a site in Wisconsin that was once a small pool at the base of an island cliff face.
The specimens belong to the so-called Waukesha Biota, and were recovered from layers older than those from Scotland yielding Dolichophonus loudonensis, which was previously accepted as the oldest known scorpion.
Professor Babcock, Otterbein University’s Dr. Andrew Wendruff and their colleagues examined the fossils under a microscope, and took detailed, high-resolution photographs of the fossils from different angles.
They were able to identify the appendages, a chamber where the animal would have stored its venom, and the remains of its respiratory and circulatory systems.
“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,” Professor Babcock said.
“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. It’s a groundbreaking discovery.”
The discovery is reported in a paper in the journal Scientific Reports.
A.J. Wendruff et al. A Silurian ancestral scorpion with fossilised internal anatomy illustrating a pathway to arachnid terrestrialisation. Sci Rep 10, 14; doi: 10.1038/s41598-019-56010-z