Sea Scorpions ("Eurypterids") are a group of extinct arthropods that may
possibly predate the earliest fishes.
are not true scorpions (which are part of the class Arachnida), but
are believed to be related to the Arachnids and Xiphosura (horseshoe crabs)
- indeed, historically, they have often been classified together with
horseshoe crabs as "Merostomata".
The earliest fossils of
Sea Scorpions date from the Ordovician period, about 460 million years
ago, although an earlier trace
dated to the Cambrian period, about 510 million years ago, is evidence
of a land living predatory arthropod, which may well be an early
Sea Scorpions were predators. They evolved in warm shallow seas, but in
later periods they tended to live in freshwater or brackish water, rather
than the sea. The fossils
of Sea Scorpions are found throughout the world, and it is thought
possible that some species may have been amphibious - coming on to land
for part of their lifecycle, and probably capable of breathing in
both water and air.
In life, Sea Scorpions had a semicircular carapace, a jointed section
containing twelve body segments, and a long tail which often tapered
and ended with a spine. The spine on the tail, was in some cases
spiked, but it is unclear whether it could have been venomous.
Sea Scorpions had a pair of compound eyes, and a paid of smaller eyes
("ocelli") between them.
Attached to the carapace were paddles, and these could have been used
for swimming, and possibly digging. Sea Scorpions also had two large
claws at the front ("chelicerae"), and four pairs of jointed legs -
suggest that some species may have used six-legged (hexapodous) and others
eight-legged (octopodous) gaits.
Most species of Sea Scorpions were quite small, less than 8 inches (20 centimeters)
in length. However there were also some larger types - the genus Jaekelopterus,
seems to have included animals up to about 8 feet (2.5 meters) in length.
Eurypterus remipes, a species of Sea Scorpion has been the State of Fossil
of New York.
Sea Scorpions were arthropods that lived in the seas between 510 and 248 million years ago
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