Fossil shows giant sea scorpion was a top predator

Palaeontologists have discovered the fossil remains of an unknown species of sea scorpion that does a really good imitation of a sea monster.

It lived 460 million years ago and was more than 1.5 metres long, making it a top predator of its day, say scientists who dug it out of rocks in a riverbed in Iowa, US.

The previously unknown species was "incredibly bizarre", said Dr James Lamsdell from Yale University, the lead author on a report published on Tuesday in the open access journal BMC Evolutionary Biology.

It is now the oldest known species of eurypterid - ancient sea scorpions that are related to modern day spiders and ticks.

Its discoverers named it Pentecopterus decorahensis, given its resemblance in outline to ancient Greek warships called penteconters.

Capturing prey

This is not a creature you would have wanted to encounter if in the sea for a swim, given its size and collection of forelimbs designed for capturing prey.

The scientists however are even more excited about the high degree of fossil preservation involved with the find. Its outer shell could be peeled away to reveal microscopic details of what lay beneath.

“This shows an amazing amount of detail, such as the patterns of small hairs on the legs,” says Lamsdell. “At times it seems like you are studying the shed skin of a modern animal - an incredibly exciting opportunity for any palaeontologist.”

This version of the monster is at least 10 million years older than the previously oldest eurypterid yet found, the scientists say.