The fossil of a previously unknown species of 'sea scorpion' has been discovered in Iowa. (PATRICK LYNCH - YALE UNIVERSITY)

Two words you probably don't want to hear in one sentence? Sea scorpion. Well, happy Tuesday.

Scientists have discovered the world's oldest specimen of (yikes) sea scorpion in an ancient meteor impact crater in Iowa, and it's a real doozy.

About 460 million years ago (back when Iowa was an ocean, naturally) the creature Pentecopterus decorahensis skittered about on the ocean floor. Described in a study published Monday in BMC Evolutionary Biology, the sea scorpion is 10 million years older than any previously discovered member of its group. And, at an estimated 5.5 feet long, it's one of the biggest, too.

“This is the first real big predator,” lead study author and Yale University researcher James Lamsdell told the Associated Press.

[This freaky ancient worm shows what spider and insect ancestors might have looked like]

Based on the complexity of the weird creature's body, the researchers say, it probably wasn't the first sea scorpion to join the seas. So it could push the origin of its group -- eurypterids, extinct relatives of arachnids -- back even further.

Fossilized remains of the Pentecopterus’s many limbs. (James Lamsdell)
Fossilized remains of the Pentecopterus’s many limbs. (James Lamsdell)

"The new species is incredibly bizarre. The shape of the paddle -- the leg which it would use to swim -- is unique, as is the shape of the head. [The scorpion is] also big -- over a meter and a half long," Lamsdell said in a statement.

The new species -- named for an ancient Greek warship called the penteconter, which it loosely resembles in body shape -- was most likely a fierce predator, based on its large front arms covered in long spines, similar to ones that horseshoe crabs use to handle their food. Meanwhile other, rear-facing legs covered in tiny hairs for sensing the environment would have helped it move about the sea.


Pentecopterus decorahensis. (James Lamsdell)

The creatures’ fossilized exoskeletons (the hard outer shell like those of cockroaches and crabs) were incredibly well-preserved, Lamsdell said in a statement. Scientists could basically peel them off of the rock and study them under a microscope, revealing details about what the animals looked like and how they moved.

“At times it seems like you are studying the shed skin of a modern animal,” he said, “an incredibly exciting opportunity for any paleontologist.”

A cool find to be sure, but we're glad that sea scorpions had their heyday half a billion years ago.

Read More:

Newly discovered dolphin hints at ancient transition from oceans to rivers

This invasive fish can live for days on land, dragging itself along with its gills

Ancient filter-feeding giants hint at the evolution of today’s insects

Four-limbed, long-fingered snake hints at a creepy crawly evolutionary journey

Bone-white ancient shells reveal their dazzling colors under UV light