Eurypterid

The eurypterids were the largest known arthropods that ever lived. They are members of the extinct class Eurypterida and predate the earliest fishes. The largest, such as Pterygotus, reached 2 m or more in length, but most species were less than 20 cm. They were formidable predators that thrived in warm shallow water in the Cambrian to Permian from 510 to 248 million years ago. Eurypterids were the most fearsome swimming predators of the Palaeozoic. Although called "sea scorpions", only the earliest ones were marine (most lived in brackish or freshwater), and they were not true scorpions. The move from the sea to fresh water probably occurred by the Pennsylvanian period.

Eurypterus is perhaps the most well-known genus of eurypterid, of which 200 fossil species are known. The genus Eurypterus was created in 1825 by James Ellsworth DeKay, a zoologist. He recognized the arthropod nature of the first ever described eurypterid specimen found by Dr. S. L. Mitchell. In 1984, Eurypterus remipes was named the State Fossil of New York.

Body structure

The typical eurypterid had a large, flat, semicircular carapace, followed by a jointed section, and finally a tapering, flexible tail, with a long spine at the end. Behind the head of the eurypterids were twelve body segments. These segments are formed by a dorsal plate called tergite, and a ventral plate called sternite. The tail, which is spiked, and in some species may have been used to inject venom, like in modern scorpions, is known as the telson. Some eurypterids have paddles, which were used to propel themselves through water. Some argue that the paddles were also used for digging. Underneath, in addition to the pair of swimming appendages the creature had 4 pairs of jointed legs for walking, and two small claws at the front, chelicerae. Other features, common to ancient and modern arthropods of this type, include one pair of compound eyes and a pair of smaller eyes called ocelli.

Although many eurypterids had legs too tiny to do more than allow them to crawl over the sea bottom, a number of forms had large stout legs, and were clearly capable of terrestrial locomotion (like land crabs today). While functional studies suggest that eurypterids used out-of-phase walking techniques, their trackways indicate that they used in-phase, hexapodous (six-legged) and octopodous (eight-legged) gaits. Some species may have been amphibious, emerging onto land for at least part of their life cycle. They may have been capable of breathing both in water and in air.

Eurypterid fossils

Eurypterid fossils have been found on nearly every continent. Locations currently producing excellent fossils include western New York State and southern Ontario, Canada, in Silurian rocks. Although relatively rare, the fossils are famous for excellent preservation. People seeking eurypterid fossils commonly search at Ridgemount Quarry, in Fort Erie, Ontario Canada.

Among the largest are the hibbertopterina, named after the British Dr Hibbert, who described Hibbertopterus scouleri at a limestone quarry in East Kirkton, Scotland, in 1836. Fossil tracks made by a 1.6m Hibbertopterus were identified in 2005 (Whyte, 2005).

Eurypterids are related to the modern marine horseshoe crabs and land scorpions. About two dozen families of eurypterids are known. They went extinct in the Permian-Triassic extinction event.

Classification after Tollerton 1989

There are more than 300 species of sea-scorpions known. These have been classified in more than 60 genera and about 20 families.

Glyptoscorpioidae

Glyptoscorpiidae
- Glyptoscorpius
  - G. perornatus
Belinuropsidae
- Belinuropsis
  - B. wigodensis

Slimonioidea

Slimoniidae
- Slimonia
  - S. acuminatus
- Himantopterus
  - H. acuminata

Hughmillerioidea

Hughmilleriidae
- Hastimima
  - H. whitei
- Hughmilleria
  - H. socialis
  - H. norvegica
  - H. bellistriata
- Salteropterus
  - S. abbreviatus
- Grossopterus
  - G. overathi
- Lepidoderma
  - L. mansfieldi
  - L. mazonense
''Carcinosomatidae
- Carcinosoma
  - C. newlini
  - C. vaningeni
  - C. scorpionis
Adelophthalmidae
- Adelophthalmus
  - A. imhofi
- Lepidoderma
  - L. imhofi

Mixopteroidea

Mixopteridae
- Mixopterus
  - M. multispinosus
  - M. kiaeri
Lanarkopteridae

Megalograptoidea

Megalograptidae
- Megalograptus
  - M. welchi
  - M. ohioensis
- Echinognathus
  - E. clevelandi

Eurypteroidea

Eurypteridae
- Eurypterus
  - E. clevelandi
  - E. cestrotus
  - E. remipes
  - E. fischeri
  - E. kokomoensis
  - E. boyli
  - E. ? abbreviatus
  - E.? overathi
- Onychopterella
  - O. kokomoensis
- Tylopterella
  - T. boyli
Dolichopteridae
- Dolichopterus
  - D. macrocheirus
- Strobilopterus
  - S. princetoni
Erieopteridae

Stylonuroidea

Stylonuridae
- Stylonurus
  - S. powriei
  - S. dolichopteroides
  - S. logani
  - S. macrophthalmus
  - S. scoticus
  - S.? multispinosus
- Drepanopterus
  - D. pentlandicus
  - D. longicaudatus
- Brachyopterus
  - B. stubblefieldi
  - B. pentagonalis
- Ctenopterus
  - C. cestrotus
- Tarsopterella
  - T. scoticus
- Melbournopterus
  - M. crossotus
- Campulocephalus
  - C. oculatus
  - C. scouleri

Dolichocephala

- Claypole
  - C.? lacoana
Drepanopteridae
Parastylonuridae
Laurieipteridae

Kokomopteroidea

Kokomopteridae
Hardieopteridae

Brachyopterelloidea

Brachyopterellidae

Rhenopteroidea

Rhenopteridae
- Rhenopterus
  - R. diensti

Mycopteropoidea

Mycteropidae
- Mycterops
  - M. scabrosus
  - M. mathieui
Woodwardopteridae
- Woodwardopterus

Pterygotoidea

Jaekelopteridae
Pterygotidae
- Pterygotus
  - P. (P.) rhenaniae
  - P. (P.) anglicus
  - P. (A.) buffaloensis
  - P. (A.) bohemicus
  - P. (P.) osiliensis
  - P. (P.) bilobus
- Acutiramus
- Erettopterus
- Himantopterus

Willwerathia (incertae sedis)
Tylopterella (incertae sedis)
Tarsopterella (incertae sedis)
Pittsfordipterus (incertae sedis)
Dorfopterus (incertae sedis)
Melbournopterus (incertae sedis)
Hallipterus (incertae sedis)
Megarachne (incertae sedis)
Palmichnium (incertae sedis)
Waeringoopterus (incertae sedis)

References

Ciurca, Samuel J. (1998). The Silurian Eurypterid Fauna (http://www.eurypterid.net/ ). Retrieved July 25, 2004.
Clarke, John M. & Rudolf R. "The Eurypterida of New York". Albany: New York State Education Department, 1912.
Whyte, Martin A. "Palaeoecology: A gigantic fossil arthropod trackway". Nature 438, 576-576 (01 December 2005)

Prehistoric arthropods

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Body structure

Eurypterid fossils

See also

References