Temporal range: Ordovician–Permian
|Eurypterid from Ernst Haeckel's
Kunstformen der Natur (1904)
The largest, such as Jaekelopterus, reached 2½ metres in length, but most species were less than 20 cm (8 inches). They were the largest arthropods of all time. They were predators which thrived in the warm, shallow seas and lakes of the Ordovician to the Permian periods, around 460 to 248 million years ago. Recent research suggsts their eyesight was not very good.
The move from the sea to fresh water probably occurred by the Pennsylvanian period. Eurypterids went extinct during the Permian–Triassic extinction event 251 million years ago, and their fossils have a near global distribution.
The typical eurypterid had a large, flat, semicircular carapace, followed by a jointed section, and finally a tapering, flexible tail, most ending with a long spine at the end (Pterygotus, though, had a large flat tail, possibly with a smaller spine). Behind the head of the eurypterids were twelve body segments. These segments are formed by a dorsal plate, called a tergite, and a ventral plate, called a sternite. The tail, known as the telson, is spiked in most eurypterids.
A recent discovery of a new fossil species of eurypterid, Pentecopterus, has been made. It is two meters long, and lived 467 million years ago, in the Middle Ordovician period.
Images for kids
Megarachne, a eurypterid closely related to Hibbertopterus from the Late Carboniferous. It was originally described as a spider - the largest to have ever existed - hence its scientific name, which translates to "great/large spider".
Mixopterus, a eurypterid of the Silurian
Eurypterus fossil from the Bertie Waterlime (Upper Silurian) of New York.
Eurypterid Facts for Kids. Kiddle Encyclopedia.