Giant Extinct Sea Scorpions Crossed the Oceans – 08/29/2024 – Science

Most modern scorpions could fit in the palm of your hand. But in the oceans of the Paleozoic Era, more than 400 million years ago, animals known as sea scorpions were apex predators that could grow to be larger than a person.

“They were operating as efficiently as sharks,” said Russell Bicknell, a paleontologist at the American Museum of Natural History.

New research by Bicknell and colleagues, published Saturday in Gondwana Journal of Research Based on Australian fossils, he reveals that the largest sea scorpions were able to cross oceans, a discovery that “completely pushes the boundaries of what we know arthropods can do,” he says.

What are commonly known as sea scorpions were a diverse group of arthropods called eurypterids. They came in many shapes and sizes, but are perhaps best known for their largest representatives, which could grow to be over 9 feet long. With massive claws, a powerful exoskeleton, and a powerful set of swimming legs, the largest sea scorpions probably ruled the seas.

Although these arthropods were fearsome to Paleolithic prey, they went extinct without much fanfare. The fossil record of eurypterids peaked in the Silurian period, which began about 444 million years ago, and then disappeared abruptly after the end of the Devonian period, about 393 million years ago.

This sudden turn of fate has left scientists baffled.

“They show up, they start doing well, they get really big and then they go extinct,” said James Lamsdell, a paleobiologist at West Virginia University who was not involved in the study. “They were dominant for a while, and then they disappeared.”

The giant arthropods have not been seen since, and a better understanding of how widespread the giant sea scorpions were could lay the groundwork for explaining why they disappeared.

Most eurypterid fossils have come from North America and Europe, with some recently discovered in China. Although some eurypterid fossils have been previously reported from Australia, they were too broken and obscure to be determined as being from the largest sea scorpion species.

Bicknell’s study documents a new set of eurypterid fossils from Australia. They are also fragments, but he doubted they could be identified.

Closer examination revealed that the fragments were mostly exoskeletons, including a possible headpiece with hints of an eye. Bicknell was confident enough about the fragments to attribute them to two species of eurypterid: Pterygotus and the largest known sea scorpion, Jaekelopterus.

Bicknell’s analysis of the rock formations in which the fossils were found showed that they were essentially identical to those found on the other side of the world: shallow seas and deltas around the edges of continents. One group of fossils was found with armored fish, and another contained some fossilized feces containing fragments of trilobites, suggesting that sea scorpions could have fed on crunchy prey.

The fragments are better than previously found, Lamsdell said, although the discovery of more specimens in Australia would help strengthen the case.

If Bicknell is right, the fossils extend the range of the largest sea scorpions to the ancient supercontinent of Gondwana, where they have never been found before. The discovery also supports the ability of sea scorpions to cross oceans, no mean feat. At the time, the journey between Gondwana and the supercontinent of Euramerica could have taken thousands of miles, depending on the route.

“It’s really cool to see that, yes, they were traveling so far,” Bicknell said. “They actually made it to Gondwana.”

Bicknell hopes future studies will reveal whether the giant sea scorpions arrived in a one-time migration event or moved seasonally.

The fact that giant sea scorpions made this journey suggests that gigantism could have played an important role in migration. It’s possible that animals simply needed a large body to survive in the oceans, like today’s oceanic sharks and whales, Lamsdell said. And once they got big enough, they could make the crossing.

But why the large size of sea scorpions allowed them to become such a global success and then go extinct after a short geological period remains a mystery. Better control of their range will direct scientists to new places to look for fossils, which in turn could help clarify matters.

“Over time, there will be more discoveries,” Lamsdell said. “Then we will have a better idea of ​​what is happening to these animals.”