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Giant ‘sea scorpion’ fossil discovered Undersea in Iowa



The fossil of a previously unknown species of ‘sea scorpion’, measuring over 1.5 meters long, has been discovered in Iowa, USA.

Dating back 460 million years, it is the oldest known species of eurypterid (sea scorpion) – extinct monster-like predators that swam the seas in ancient times and are related to modern arachnids.

The authors named the new species Pentecopterus decorahensis after the ‘penteconter’ – an ancient Greek warship that the species resembles in outline and parallels in its predatory behavior.

Lead author, James Lamsdell from Yale University, said: “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. It’s also big – over a meter and a half long!”

He adds: “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. 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.”

The new eurypterid species is represented by more than 150 fossil fragments, excavated from the upper layer of the Winneshiek Shale in northeastern Iowa – a 27 meter thick sandy shale located within an ancient meteorite impact crater and mostly submerged by the Upper Iowa River.

Some large body segments suggest a total length of up to 1.7 meters, making Pentecopterusthe largest known eurypterid from its era.

Pentecopterus is about 460 million years old, making it ten million years older than the previous oldest record of the eurypterid group.


The findings have been published in the journal BMC Evolutionary Biology.

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