Eurypterids
The eurypterids (sea scorpions) include the largest known arthropods that ever lived (with the possible exception of Arthropleuridae). They are members of the extinct class Eurypterida (Arachnomorpha, Chelicerata) and predate the earliest fishes. The largest, such as Jaekelopterus, reached 2 meters or more in length, but most species were less than 20 centimeters. They were formidable predators that thrived in warm shallow water in the Cambrian and survived to the Permian from 510 to 248 million years ago. Although called "sea scorpions", only the earliest ones were marine (most lived in brackish or freshwater), and they were true scorpions. They moved from the sea to fresh water probably by the Pennsylvanian period.
http://i272.photobucket.com/albums/jj171/Azjahh/Geology/Eurypterid.jpg
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 tergite, and a ventral plate called sternite. The tail, known as the telson, is spiked in most eurypterids like in modern scorpions and in some species it may have been used to inject venom, but so far there is no certain evidence any eurypterids were venomous. Most eurypterids have paddles toward the end of the carapace and beyond, which were used to propel themselves through water. Some argue that the paddles were also used for digging. It is possible that it was used for both. Underneath, in addition to the pair of swimming appendages the creature had 4 pairs of jointed legs for walking, and two large claws at the front, chelicerae. The walking legs had odd hairs, similar to modern day crabs. 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, in between the other larger 2 eyes.
Eurypterid fossils have a near global distribution. Among the largest eurypterids are the Hibbertoptermina, named after the British palaeontolgist S. Hibbert, who described Hibbertopterus scouleri at a limestone quarry in East Kirkton, Scotland, in 1836. Fossil tracks were identified recently in East Lothian, Scotland, as made by a 1.6 meter long Hibbertopterus (Whyte, 2005).
Eurypterids are related to the modern marine horseshoe crabs. About two dozen families of eurypterids are known. They went extinct during the Permian-Triassic extinction 251.4 million years ago. A predatory arthropod whose traces are known as Protichnites, found in Cambrian strata dating from 510 million years ago, is a possible stem group eurypterid, and is among the first evidence of animals on land.
In 2007, a group paleontologists led by Simon Braddy at the University of Bristol discovered a sea scorpion larger than a human being, which was claimed to have been the largest arthropod which ever lived. This discovery was made in a 390 million year old rock containing the fossil of a huge claw or chelicera.
The eurypterids (sea scorpions) include the largest known arthropods that ever lived (with the possible exception of Arthropleuridae). They are members of the extinct class Eurypterida (Arachnomorpha, Chelicerata) and predate the earliest fishes. The largest, such as Jaekelopterus, reached 2 meters or more in length, but most species were less than 20 centimeters. They were formidable predators that thrived in warm shallow water in the Cambrian and survived to the Permian from 510 to 248 million years ago. Although called "sea scorpions", only the earliest ones were marine (most lived in brackish or freshwater), and they were true scorpions. They moved from the sea to fresh water probably by the Pennsylvanian period.
http://i272.photobucket.com/albums/jj171/Azjahh/Geology/Eurypterid.jpg
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 tergite, and a ventral plate called sternite. The tail, known as the telson, is spiked in most eurypterids like in modern scorpions and in some species it may have been used to inject venom, but so far there is no certain evidence any eurypterids were venomous. Most eurypterids have paddles toward the end of the carapace and beyond, which were used to propel themselves through water. Some argue that the paddles were also used for digging. It is possible that it was used for both. Underneath, in addition to the pair of swimming appendages the creature had 4 pairs of jointed legs for walking, and two large claws at the front, chelicerae. The walking legs had odd hairs, similar to modern day crabs. 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, in between the other larger 2 eyes.
Eurypterid fossils have a near global distribution. Among the largest eurypterids are the Hibbertoptermina, named after the British palaeontolgist S. Hibbert, who described Hibbertopterus scouleri at a limestone quarry in East Kirkton, Scotland, in 1836. Fossil tracks were identified recently in East Lothian, Scotland, as made by a 1.6 meter long Hibbertopterus (Whyte, 2005).
Eurypterids are related to the modern marine horseshoe crabs. About two dozen families of eurypterids are known. They went extinct during the Permian-Triassic extinction 251.4 million years ago. A predatory arthropod whose traces are known as Protichnites, found in Cambrian strata dating from 510 million years ago, is a possible stem group eurypterid, and is among the first evidence of animals on land.
In 2007, a group paleontologists led by Simon Braddy at the University of Bristol discovered a sea scorpion larger than a human being, which was claimed to have been the largest arthropod which ever lived. This discovery was made in a 390 million year old rock containing the fossil of a huge claw or chelicera.