NEW YORK: The newly discovered sea scorpion lived 467 million years ago and grew to a length of nearly six feet.
It was one of the most powerful ocean predators of its time, with an exoskeleton “helmet” shielding its head, a sleek narrow body, and large grasping limbs for trapping prey.
Scientists named the beast Pentecopterus decorahensis, after the “penteconter” an ancient Greek ship rowed by 50 oarsmen that saw service in the Trojan War.
Although they look like relatives of lobsters or crabs, sea scorpions, or “eurypterids”, were the ancestors of modern spiders.
Lead researcher Dr James Lamsdell, from Yale University in the US, 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!”
Perhaps most surprising is the fantastic way it is preserved, he added. 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 palaeontologist.”
The creature, described in the journal BMC Evolutionary Biology, was identified from more than 150 fossil fragments excavated from Winneshiek Shale sedimentary rocks in north-east Iowa, US.
Some of the animal’s body segments suggest a total length of up to 1.7 metres (5.57 feet), making it the largest known eurypterid from its era.
It is also 10 million years older than any other sea scorpion discovered to date.
Exceptional preservation of the exoskeleton has allowed scientists to interpret the role of fines structures such as scales, follicles and stiff bristles.
The creature’s rearmost limbs are covered in dense setae, or bristles. These may have contributed to its swimming ability, or had a sensory function.
Spines on some limbs appear similar to those of horseshoe crabs, which use them to aid food processing.
“Pentecopterus is large and predatory, and eurypterids must have been important predators in these early Palaeozoic ecosystems,” said Dr Lamsdell.
During the Ordovician period, when Pentecopterus was alive, invertebrates ruled the oceans and the first animals were only just starting to colonise the land.
Early fish at this time grew no longer than about 12 inches and were jawless. They would have been no match for a giant sea scorpion.