Animals of the Past

Sea scorpions

Timeline: 541–250 million years ago

Geographical range, habitat: former Euramerica shallow coastal waters

Body length: 20 cm – 2.5 m

Eurypterids, or sea scorpions, are an extinct group of Palaeozoic aquatic arthropods. Based on fossils that have been found, more than 200 species of Eurypterids are known, the most common of which was probably Eurypterus giganteus. Some larger specimens of this species reached
130 cm in length.The largest known Eurypterid was Jaekelopterus rhenaniae, which probably measured about
2.5 m in length and had terrifying, 40 cm long claws.

Anatomy

The opistosome of sea scorpions
was covered with a rigid carapace.
Their first pairs of legs were for walking and feeding, while their last pair of legs were modified into swimming legs.

Classification

Although due to their elongated postabdomens and telsons, that is, the needle-like appendages, they looked similar to scorpions, they were not true scorpions.

They belonged to the group Chelicerata and they were related to Arachnids.

• In 1984 Eurypterus remipes became the state fossil of New York.
• Eurypterids are the largest known arthropods ever to have lived.

Lifestyle

They were predators inhabiting warm, shallow coastal areas. Although they are commonly called sea scorpions,
only the earliest ones were marine,
later ones lived in freshwater.

Eurypterus giganteus

Probably the most common species;
some larger specimens of this species reached 130 cm in length.

Mixopterus kiaeri

This species was characterised
by two sets of strong walking legs with long needles on them.

Megalograptus

This species also had well-developed walking legs, and some specimens reached 170 cm in length.

Jaekelopterus rhenaniae

It was the largest known Eurypterid; it probably measured about 2.5 m in length and had terrifying, 40 cm long claws.