| Pterygotidae Temporal range: Late Silurian – Late Devonian,
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| Fossil chelicera of Acutiramus cummingsi. The massive chelicerae of the pterygotids were their primary distinguishing feature. | |
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| Left to right, top to bottom: Jaekelopterus rhenaniae, Erettopterus bilobus, Pterygotus anglicus, Acutiramus macrophthalmus, Ciurcopterus ventricosus | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Chelicerata |
| Order: | †Eurypterida |
| Infraorder: | †Diploperculata |
| Superfamily: | †Pterygotioidea |
| Family: | †Pterygotidae Clarke & Ruedemann, 1912 |
| Type species | |
| †Pterygotus anglicus Agassiz, 1844
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| Genera | |
| Synonyms | |
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Pterygotidae (the name deriving from the type genus Pterygotus, meaning "winged one") is a family of eurypterids, an extinct group of aquatic arthropods. They were members of the superfamily Pterygotioidea. Pterygotids were the largest known arthropods to have ever lived with some members of the family, such as Jaekelopterus and Acutiramus, exceeding 2 metres (6.6 ft) in length. Their fossilized remains have been recovered in deposits ranging in age from 428 to 372 million years old (Late Silurian to Late Devonian).
One of the most successful groups of eurypterids, the pterygotids were the only eurypterid family to achieve a truly worldwide distribution. Several evolutionary innovations made the pterygotids unique among the eurypterids, with large and flattened telsons (the posteriormost division of the body) likely used as rudders to provide additional agility and enlarged chelicerae (frontal appendages) with claws. These claws were robust and possessed teeth which would have made many members of the group formidable predators. The strange proportions and large size of the pterygotid eurypterids led to the quarrymen who discovered the very first fossil remains of the group to give them the common name "Seraphims".
Studies on the cheliceral morphology and compound eyes of the pterygotids have revealed that the members of the group, despite overall morphological similarities, were highly divergent in their ecological roles. Pterygotid ecology ranged from generalized predatory behaviour in basal members of the group, such as Erettopterus, to active apex predators, such as Jaekelopterus and Pterygotus, and ambush predators and scavengers, such as Acutiramus .
Some researchers have suggested that the pterygotid eurypterids evolved in something akin to an "arms race" with early vertebrates, that the evolution of heavy armor in the ostracoderms could be attributed to pressure from pterygotid predation and that later pterygotid decline could be attributed to subsequent evolutionary trends in fish. This hypothesis is mostly considered as far too simplistic of an explanation by modern researchers. Detailed analyses have failed to find any correlation between the extinction of the pterygotids and the diversification of the vertebrates.