Pterygotus anglicus

Pterygotus is a genus of giant predatory eurypterid, a group of extinct aquatic arthropods. Fossils of Pterygotus have been discovered in deposits ranging in age from Late Silurian to Early Devonian, and have been referred to several different species. Fossils have been recovered from four continents; Australia, Europe, North Americaand South America, which indicates that Pterygotus might have had a nearly cosmopolitan (worldwide) distribution. The type species, P. anglicus, was described by Swiss naturalist Louis Agassiz in 1839. Agassiz mistakenly believed the remains were of a giant fish, with the name Pterygotus translating to "winged fish". He would only realize the mistake five years later in 1844. Pterygotus was among the largest eurypterids. Isolated fossil remains of a large chelicera (frontal appendage) suggests that the largest known species, P. grandidentatus, reached a body length of 1.75 metres (5.7 ft). Several other species, notably P. impacatus at 1.65 metres (5.4 ft) and P. anglicus at 1.6 metres (5.2 ft) were similarly gigantic. Pterygotus was surpassed in size by other giant eurypterids. Acutiramus was able to surpass 2 metres (6.6 ft), and Jaekelopterus could reach 2.6 metres (8.5 ft). Many species were considerably smaller than the largest species, such as P. kopaninensis at 50 centimetres (20 in). Like its close relative Jaekelopterus, Pterygotus was a large and active predator noted for its robust and enlarged cheliceral claws that would have allowed it to puncture and grasp prey and a visual acuity(clarity of vision) comparable to that of modern predatory arthropods.

With the largest species, P. grandidentatus, reaching a body length of 1.75 metres (5.7 ft), Pterygotus was among the largest known eurypterids to have existed, though some of its close relatives (such as Acutiramus and Jaekelopterus) surpassed it in length. Though there were a few gigantic species, many species were considerably smaller in size. The smallest species, P. kopaninensis, measured just 50 centimetres (20 in) in length. Pterygotus is classified as part of the pterygotid family of eurypterids, to which it lends its name, a group of highly derived eurypterids of the Silurian to Devonian periods that differ from other groups by a number of features, perhaps most prominently in the chelicerae (the first pair of limbs) and the telson. The chelicerae of the Pterygotidae were enlargened and robust, clearly adapted to be used for active prey capture and more similar to the claws of some modern crustaceans, with well developed teeth on the claws, than to the chelicerae of other eurypterid groups. Unlike most of the rest of the body, which was covered in a scale-like ornamentation like other pterygotid eurypterids, the claws lacked any type of ornamentation. Additionally, the end points of the claws were round and curved unlike the sharp points present at the ends of the claws of the related Erettopterus. The pterygotid telsons were flattened and expanded, likely used as rudders when swimming. Their walking legs were small and slender, without spines, and they were likely not capable of walking on land. Pterygotus is distinguishable from other pterygotids by the curved distal margin of the chelae (claws). The prosoma (head) is subtrapezoidal (a trapezoid with rounded corners), with compound eyes located near the edge of the front corners. The telson (the posteriormost segment of its body) has a pronounced dorsal carina (or keel) running down its center, terminating in a short spine.