Giant scorpions once ruled the seas — and could cross entire oceans

When asked to rate giant sea scorpions on a scale of one to terrifying, Russell Bicknell rated them about an eight.

“I think it depends on how you define scary,” said Bicknell, a paleobiologist at the American Museum of Natural History. As it happens guest host is Susan Bonner.

“They look pretty cool to me.”

Sea scorpions roamed the oceans more than 400 million years ago. Some species were larger than humans, and their powerful claws and thick exoskeletons made these apex predators a force to be reckoned with.

As if that wasn’t enough, new research shows they were also globetrotters and endurance swimmers.

The study by Bicknell and his colleagues was published Saturday in the journal Gondwana Research. The results expand our understanding of the ancient creatures’ ranges and could provide clues to what caused the extinction of these once-fearsome sea bugs.

A mighty migration

Eurypteridae, commonly known as sea scorpions, were a group of over 200 species of arthropods that inhabited the oceans until their abrupt extinction about 393 million years ago.

Their fossils have been found mainly in what is now North America and Europe, with some being discovered just last year in China.

Although some eurypterid fossils had been found in Australia before, Bicknell says they were too fragmented to classify with confidence. But he and his team examined two new sets of fossils, both found in Australia.

Though the specimens were still fragmented, they were intact enough that scientists could identify them as Pterygotus and Jaekelopterus —or, as Bicknell describes them, “the really, really big ones.”

Pterygotus could reach 1.7 meters (5.7 feet) in length, while Jaekelopterus could reach 2.5 meters (8 feet) in length.

“Much larger than a human,” Bicknell said.

These findings extend the known range of giant sea scorpions and provide the first evidence of their existence in Gondwana, an ancient supercontinent.

Because giant sea scorpion fossils come mainly from the United States and Europe, Bicknell and his colleagues speculate that they must have traveled “quite a long way,” thousands of miles, to what is now Australia, where they were found fossilized along with large fish and trilobites—most likely their food.

“That tells us that these animals were actually very efficiently built to travel really, really far. So they probably covered a similar distance to some whales,” Bicknell said.

“And that’s really, really exciting because it’s really, really hard for us to tell how these animals could have migrated, or whether they did migrate, without these kinds of fossils.”

It is unclear whether this migration was a one-time occurrence, or whether they traveled back and forth seasonally. However, their remains have been found in similar ocean environments to other large eurypterid fossils.

“The animals were able to essentially migrate into the oceans around Australia and then move between these environments, which we think are sort of like very, very large deltas — freshwater, marine,” Bicknell said.

Why did they die out?

Scientists don’t know what killed off the once-dominant eurypterids, and Bicknell’s research doesn’t solve that mystery. But it could provide a starting point for further research.

“It allows us to understand the scope of the idea called gigantism — or things getting really, really big — and it allows us to understand what gigantism as an evolutionary process can produce,” he said.

Sea scorpions, he said, seem to evolve, getting bigger and bigger until they reach about 8 feet, “and then they just drop off.”

Why, he claims, is not clear.

“It could be an environmental issue. It could be an ecological issue, so they’re in some ways competing with other animals. Or they just went too far and that led to their extinction,” he said. “That’s kind of an open question.”

James Lamsdell, a paleobiologist at West Virginia University who was not involved in the study, told The New York Times that the fossils Bicknell and his team examined were in better condition than those previously found in Australia.

But he added that finding more specimens in Australia would strengthen the thesis that giant sea scorpions roamed the shores of ancient Gondwana.

He believes the research could help scientists determine where more eurypterid fossils are found in Australia, which in turn could help solve the mystery of why these seemingly evolutionarily successful creatures disappeared so suddenly.

“There will be more discoveries over time,” he said. “Then we will have an even better idea of ​​what is happening to these animals.”