‘Incredibly Bizarre’ Giant Sea Scorpion Discovered in Iowa Fossil

It lived a half-billion years ago, was as large as a man, and feasted on pretty much everything that was smaller than it was — which was most things.

A newly discovered species of giant sea scorpion, recently unearthed in a fossil in Iowa, is the oldest such animal ever found, and the largest sea scorpion of its time — an apex predator in the ancient ocean that once covered the American Midwest.

“The new species is incredibly bizarre,” said Dr. James Lamsdell, a paleontologist from Yale University, who reported the find in a press statement.

“It’s also big, over a meter and a half long!”

Though not true scorpions, sea scorpions were aquatic arthropods that thrived from 240 million years ago all the way back to 460 million years ago — which is the record-setting age of the newly found specimen.

sea scorpion
An artist’s rendering depicts two Pentecopterus, the oldest sea scorpion ever found, and the largest such animal of its age. (Courtesy Patrick Lynch, Yale University)

Most sea scorpions were scarcely more than 20 centimeters long [8 inches], but this new species reached lengths of up to 1.7 meters [5.5 feet].

This — along with its hardy exoskeleton and eight nimble limbs — likely earned it a comfortable berth near the top of the food chain, researchers say.

Paleontologists found the fossil in a shale deposit in northeastern Iowa, which was inundated with warm seas, as was much of the continent, during the Ordovician Period. [Learn more about America’s watery past: “Fossil of Earliest Known ‘Jesus Lizard,’ A Reptile That Walked on Water, Discovered in Wyoming“]

So the scientists named the new animal Pentecopterus, after another historical long-tailed sea hunter: the penteconter, the 50-oared warship used by the ancient Greeks.

The fossil of Pentecopterus is in an exquisite state of preservation, Lamsdell reported, which has allowed him and his team to discover features that have never been seen before in such a creature.

“The shape of the paddle — the [rear] leg which it would use to swim — is unique, as is the shape of the head,” Lamsdell said.

The fossil is in a “fantastic” state of preservation, scientists said, allowing for the close study of joints, microstructure, and even the hair-like bristles on the animal’s limbs. (Courtesy James Lamsdell)

Moreover, the skeleton of Pentecopterus is so well preserved that the researchers can even observe some of its smallest structures, like the joints in the legs and the setae, or tiny hair like structures, that lined many of its limbs.

“The exoskeleton is compressed on the rock but can be peeled off and studied under a microscope,” Lamsdell said.

“This shows an amazing amount of detail, such as the patterns of small hairs on the legs.” [Related: “Dinosaur Blood Cells, Soft Tissue Discovered in 75-Million-Year-Old Fossils“]

Thanks to details like these, the fossil has already provided some unexpected insights, including the fact that Pentecopterus’ back legs were significantly shorter than the rest, so the animal probably walked on only six of its eight legs.

iowa sea scorpion fossil
A microscopic view reveals dozens of setae on one of Pentecopterus’ limbs. The black scale bar below is 1 millimeter. (Courtesy James Lamsdell)

And its limbs appear to have been fringed with tiny spines, much like modern horseshoe crabs — an adaptation thought to aid in feeding.

Researchers have even been able to study the tiny follicles, or pore-like pits, that its bristly setae grew out of. Judging by the follicles’ small size, the scientists think the hairs may actually have served as sensory organs.

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

[Read about another exciting find for paleontologists: “Cave Discovered in South Dakota Contains Thousands of Ice Age Fossils“]

Lamsdell and his colleagues report their findings in the journal BMC Evolutionary Biology.

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  1. vicki stone

    is this sea scorpion somehow related to the contemporary insect scorpion? Thank you

  2. kittens

    If only the ole miss archaeologist found this………

  3. Mary

    It takes great faith to believe that the fossil’s tiny hairs, a fraction of a millimeter long, were PRESERVED IN ROCK FOR 240 MILLION YEARS. Do any of today’s “thinkers” ever wonder why the mud encasing this creature turned to stone before the creature could decay???

  4. Phred

    The earth is round Mary

    1. Galaleo

      It’s an amazing thing that we are so self righteous as a species on this planet…. we are that half a fraction of a millimeter in the time of this vast world. We are in our infancy as we are as curious as a child wanting the answers to why we are here….You ask what and man will answer look into the past if you seek your future….

  5. urbain

    Is it related!