Beach-goers often fret over sharks and jellyfish, but modern day oceans are downright tame compared to Earth’s geologic past. 460 million years ago, a five-foot-long, scorpion-like monster straight out a 1950s science fiction flick ruled the seas.

Meet Pentecopterus, a fearsome predator of a bygone geologic period that paleontologists just unveiled in a new scientific paper. The sea scorpion, which grew up 1.7 meters (5.5 feet) in length, had a powerful head shield, a paddle-like tail, and large, grasping limbs for ripping apart prey. It’s no wonder scientists decided to name the beast after an ancient Greek warship — this creature was no laughing matter.

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“The new species is incredibly bizarre,” said lead study author James Lamsdell in a statement. “The shape of the paddle - the leg which it would use to swim - is unique, as is the shape of the head. It’s also big - over a meter and a half long!”

Pentecopterus reconstruction. Scale bar 10cm. Image Credit: Yale University

Pentecopterus belongs to the eurypterids, an extinct group of predatory invertebrates related to modern lobsters and spiders that lived in shallow seas and oceans during the Ordovician and Permian periods, some 460 to 248 million years ago. It’s quite possibly the largest, and certainly the oldest eurypterid known to science.

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“This shows that eurypterids evolved some 10 million years earlier than we thought, and the relationship of the new animal to other eurypterids shows that they must have been very diverse during this early time of their evolution, even though they are very rare in the fossil record,” Lamsdell told Yale News.

Pentecopterus hairs. Scale bar 1 mm. Image Credit: James Lamsdell

Pentecopterus Leg. Scale bar 1 cm. Image Credit: James Lamsdell

The sea scorpion is represented by over 150 remarkably well-preserved fossil fragments, excavated from a 27 meter-thick layer of sandy shale located in northeastern Iowa. Its discovery serves to remind us that there are still plenty of incredible beasts waiting to be dredged up from the ground. And that we’re all a bunch of major wimps for freaking out over spiders.

[Read the full scientific paper at BMC Evolutionary Biology via Yale News]


Contact the author at maddie.stone@gizmodo.com or follow her on Twitter.

Top: Artist’s impression Pentecopterus. Image Credit: Patrick Lynch - Yale University