Earth’s first big predator may have been an underwater scorpion that grew to nearly six feet in length, according to a new study.

Some 150 pieces of previously unknown fossils were recovered from the site of a meteor impact by Iowa Geological Survey geologists, under the Upper Iowa River. The creature is estimated to have lived 460 million years ago, long before the dinosaurs reigned, when Iowa was still an ocean.

First described Monday in the journal BMC Evolutionary Biology, the scorpion – named Pentecopterus decorahensis, after an ancient Greek warship – could grow to 5ft 7 inches long (170 centimeters) and had a dozen arms sprouting from its head, which it used to grab prey and push it into its mouth

“The new species is incredibly bizarre,” the study’s lead author James Lamsdell of Yale University said in a press release. “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!”

The creature’s huge size is particularly notable because of its close relation to spiders and scorpions, and its comparative largeness to other forms of sealife which it lived alongside.

“This is the first real big predator,” Lamsdell said. “I wouldn’t have wanted to be swimming with it. There’s something about bugs. When they’re a certain size, they shouldn’t be allowed to get bigger.”

Lamsdell and his colleagues believe that the Pentecopterus was a euryptid, which is an order of extinct sea scorpions related to modern scorpions, spiders and mites. The Pentecopterus is the oldest and largest of the group that has been discovered, but unlike modern land scorpions, it used its tail as a paddle to move through the water, rather than for stinging.

The creature is also notable for being incredibly well preserved, Lamsdell said in a statement.

“Perhaps most surprising is the fantastic way it is preserved – the exoskeleton is compressed on the rock but can be peeled off and studied under a microscope,” he said. “At times it seems like you are studying the shed skin of a modern animal - an incredibly exciting opportunity for any paleontologist."