page_title: Pterygotus
section_title: Classification
hierarchical_section_title: Pterygotus / Classification
caption_attribution_description: Exhibit in the Houston Museum of Natural Science, Houston, Texas, USA. Photography was permitted in the museum without restriction.
context_page_description: 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 Late Devonian, and have been referred to several different species. Fossils have been recovered from four continents; Australia, Europe, North America and South America, which indicates that Pterygotus might have had a nearly cosmopolitan 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 suggests that the largest known species, P. grandidentatus, reached a body length of 1.75 metres. Several other species, notably P. impacatus at 1.65 metres and P. anglicus at 1.6 metres were similarly gigantic. Pterygotus was surpassed in size by other giant eurypterids. Acutiramus was able to surpass 2 metres, and Jaekelopterus could reach 2.6 metres.
context_section_description: Pterygotus is classified within the family Pterygotidae in the superfamily Pterygotioidea, lending its name to both its family and its superfamily. The three most derived pterygotid eurypterids, Acutiramus, Jaekelopterus and Pterygotus, are very similar to each other. Pterygotus is particularly similar to Jaekelopterus, from which it is virtually only distinct in features of the genital appendage and potentially the telson.
  Similarities in the genital appendage could mean that the three genera are all synonyms of each other, as they had been classified in the past (as species of Pterygotus). Some differences between them have also been noted in the chelicerae, though chelicerae have been questioned as the basis of eurypterid generic distinction since their morphology depends on the lifestyles and has been observed to vary throughout ontogeny. Telson morphology is sometimes used as a distinguishing feature, though the telsons of the three derived pterygotid genera are all paddle-shaped (the telson of Jaekelopterus is triangular, but might fall into the morphological range of the other genera). An inclusive phylogenetic analysis with multiple species of Acutiramus, Pterygotus and Jaekelopterus is required to resolve whether or not the genera are synonyms of each other.
  The cladogram below is based on the nine best-known pterygotid species and two outgroup taxa (Slimonia acuminata and Hughmilleria socialis). The cladogram also contains the maximum sizes reached by the species in question, which have been suggested to possibly have been an evolutionary trait of the group per Cope’s Rule ("phyletic gigantism").
caption: Fossilized specimens of P. monroensis discovered in the Late Silurian Fiddlers Green Formation of New York, United States.
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