A new species of prehistoric scorpion from the early Siluarian period (approximately 437.5 to 436.5 million years ago) is described in a study in Scientific Reports. The findings suggest that Parioscorpio venator is the oldest-known scorpion reported to date and may have been capable of leaving its marine habitat and venturing onto land, a behaviour similar to that of present-day horseshoe crabs.
Scorpions are among the first animals to have moved from the sea onto land but because their fossil record is limited, how and when they adapted to life on land remains unclear.
Andrew Wendruff and colleagues describe two well-preserved specimens of a previously unknown fossil scorpion species discovered in the Waukesha Biota in Wisconsin, USA, which dates from the early Silurian. This makes the fossils older than Dolichophonus loudonensis, from Scotland, which was previously accepted as the oldest known scorpion species.
P. venator shows some primitive characteristics present in other early marine organisms, such as compound eyes, as well as characteristics found in present-day scorpions, such as a tail terminating in a stinger. Both P. venator specimens show details of internal anatomy, including narrow, hourglass-shaped structures that extend along much of the middle part of the body. These structures are very similar to the circulatory and respiratory systems in present-day scorpions, as well as those of modern horseshoe crabs, according to the authors.
No lungs or gills are evident in the P. venator fossils, but their similarity to horseshoe crabs, which can breathe on land, suggests that while the oldest scorpions may not have been fully terrestrial, they may have forayed onto land for extended periods of time.