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Sea scorpions

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Restoration of a group of Eurypterus. Eurypterus are believed to have lived in shallow, sandy bottoms near beaches.
Restoration of an Eurypterus. This animal was about 15 to 20 cm long.

Eurypterids, nicknamed sea scorpions, were a group of aquatic arthropods that thrived millions years ago, and are now extinct. Despite their general scorpion-like appearance, that gave them their name, eurypterids are only distant cousins of the scorpions: they are not close relatives. The eurypterids' closest relatives still living nowadays are the horseshoe crabs.

Most eurypterids were coastal marine predators, though some of them are believed to have lived in fresh, or at least brackish water. There were many species, the best-known being Eurypterus. Some eurypterids (like Pterygotus or Jaekelopterus) were among the greatest arthropods that ever lived on Earth. Jaekelopterus could have reached about 2.5 meters in length (about the size of a crocodile), and must have been a superpredator of its time.

Life history[edit | edit source]

Anatomy of an 'eurypterid.
Horseshoe crabs are close relatives to th eurypterids, that are still living nowadays.
A fossil eurypterid.

The first eurypterids appeared about 460 millions years ago, in the Silurian period, while the latest species disappeared 248 millions years ago, at the end of the Permian period, amongst many other species, during the Permian-Triassic extinction event.

Eurypterids had a body covered with a hard shell, divided in various part, as in every arthropod. The body was quite flat, elongated, and ended by a kind of spiked "tail" (named, by the scientists, a telson), that looks like a scorpion tail. The Eurypterids, however, had no sting, and are believed to have not been poisonous. The prosoma, or "head", was flat, rounded, and bear a pair of compouned eyes, that made them able to detect their preys.

Eurypterids had various pairs of limbs, some of them, bearing claws, made to catch preys, others, looking like legs, to walk on the marine floor, others ones looking like flippers, to swim in the water, and the latest bear gills that the animal used to breath.

Some of them could have been partially terrestrial, or amphibious animals : some fossils tracks are known and believed to be eurypterids'one : the show that some eurypterids could probably venture on the shoreland. Some scientists thus belive that some eurypterids could have been able to breath both in water and in the air.

Most of eurypterids were about 15 to 25 cm longs animals, but some were pretty much larger, like the famous Pterygotus, or its less-known, and even larger cousin, Jaekelopterus, that could reach about 2.5 m.

They were carnivorous predators, that hunted animals such as trilobites, a kind of very common, small arthropods at these times, or some of the first fishes (close relatives to the first ancestors of Vertebrates), such as Cephalaspis...

They shared their environments with other animals, like their believed close cousins, the horseshoe crabs ; their more far related cousins, the scorpions, to whom they are often referred, appeared about the same time, and some, as Brontoscorpio, one of the earliest known scorpio, were also aquatic animals.

But, about 268 millions years ago, a cataclysm destroyed most of living species on Earth ; even though the horseshoe crabs and scorpions passed through it, most of marine animals of these times, such as trilobites, and the eurypterids, fully disappeared.

In popular culture[edit | edit source]

  • in the TV serie Sea Monsters, the "seventh deadliest sea" is located in a shore during the Ordovician period, about 450 millions years ago. Nigel Marven discovers, among other animals, a eurypterid, Megalograptus.
  • in the documentary Walking with monster, a Brontoscorpio is attacked by a very big eurypterid. This animal is called a Pterygotus, even though (due to its size : it is said to be 2.5 meters long) it could have been mistaken with its close relative, Jaekelopterus. In a latter episode, a Megarachne appears, as a giant spider : at the time when the movie was made, Megarachne was just discovered, and was first thought to be a spider.
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