5-Foot-Long Spider Relative Found In Iowa

A human-sized prehistoric relative of spiders has just been discovered in northeastern Iowa, according to a new study.

The previously unknown species of sea scorpion, Pentecopterus decorahensis, was named after an ancient Greek warship, the penteconter, and is described in the latest issue of the journal BMC Evolutionary Biology.

“The new species is incredibly bizarre,” 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!”

Lamsdell and his colleagues excavated more than 150 fossil fragments from the ancient predator, which lived 460 million years ago, long before the first dinosaurs emerged. The site itself is noteworthy, as the fossils were entombed in thick shale located within an ancient meteorite impact crater that today is mostly submerged by the Upper Iowa River.

“Perhaps most surprising is the fantastic way it is preserved,” Lamsdell said. “The exoskeleton is compressed on the rock but can be peeled off and studied under a microscope. This shows an amazing amount of detail, such as the patterns of small hairs on the legs. At times it seems like you are studying the shed skin of a modern animal — an incredibly exciting opportunity for any paleontologist.”

He and his colleagues believe that Pentecopterus was a eurypterid (sea scorpion), which refers to a group of extinct animals related to today’s spiders, scorpions, mites and ticks. This particular species is the world’s oldest known sea scorpion.

Although the animal lived so long ago, its remains provide clues on how it lived. The structure of its rear limb paddles suggests that it used them for either swimming or digging. Since its second and third pairs of limbs seem to have angled forward, the scientists suspect that they were involved primarily in prey capture.

Its three rearmost pairs of limbs are shorter than its front pairs. This indicates that it might have walked on six legs instead of eight. The rear limbs were also covered in setae (stiff bristles), similar to what covers some modern crabs. They probably expanded the surface area of the paddles during swimming, and could have also helped the sea scorpion to feel its way around, similar to whiskers on a cat.

Huaibao Liu of the Iowa Geological Survey and the University of Iowa led the fossil dig and is a co-author of the paper.

Read more at Discovery News