The Winneshiek Shale in northeastern Iowa has revealed the oldest known and largest sea scorpion ever found in the world. The new species of eurypterid was named Pentecopterus decorahensis by James Lamsdell from Yale University who discovered the fossil.
The animal was over five feet in length and lived 460 million years ago in inland waters that are now an ancient meteorite impact crater and mostly submerged in present day Iowa. The animal was uniquely preserved in that the fossil could be peeled from the rock that it was embedded in as a single piece. The unique fossilization process allowed the researchers to examine the anatomy of sea scorpions to a degree of detail that has never been possible before.
The head and tail of the new species are uniquely large. The animal is 10 million years older than any other known species of sea scorpion. The rearmost legs and fan shaped last segment called a paddle are larger than any other species. The paddle and rear portions of the exoskeleton were fused together to facilitate speed in swimming and digging for food and shelter.
The fossil presented such detail that the hair like structures called setae, scales, and spines could be seen in detail that has never been seen before. The researchers postulate that the setae probably functioned in a sensory capacity. The animal had eight legs but walked on six. The legs were segregated according to function with the first two pairs of legs serving to hold captured prey.
