By 1859, 10 species had been assigned to the genus, and John William Salter recognized that it was possible to divide these species into subgenera based on the morphology of the telsons.
Salter erected the subgenus Pterygotus (Erettopterus) for species with a bilobed telson.
Further subgenera would be named as more differences were noted between the species, such subgenera include Pterygotus (Curviramus) and Pterygotus (Acutiramus), named in 1935 based upon features of the denticles (teeth) of the chelicerae.
Pterygotus (Curviramus) was later recognized as synonymous with Pterygotus (Pterygotus) by Leif Størmer the same year, and Erettopterus and Acutiramus would be recognized as separate, but closely related, genera (Erettopterus by Erik N. Kjellesvig-Waering in 1961, and Acutiramus by Størmer in 1974).

In 1912, the family Pterygotidae was erected by John Mason Clarke & Rudolf Ruedemann in 1912 to include the eurypterid genera Pterygotus, Slimonia, Hughmilleria and Hastimima.
The three latter genera would be reclassified as members of the Hughmilleriidae by Erik N. Kjellesvig-Waering in 1951, leaving Pterygotus and its former subgenera as the sole pterygotid eurypterids.
By 1859, 10 species had been assigned to the genus, and John William Salter recognized that it was possible to divide these species into subgenera based on the morphology of the telsons. Salter erected the subgenus Pterygotus (Erettopterus) for species with a bilobed telson. Further subgenera would be named as more differences were noted between the species, such subgenera include Pterygotus (Curviramus) and Pterygotus (Acutiramus), named in 1935 based upon features of the denticles (teeth) of the chelicerae. Pterygotus (Curviramus) was later recognized as synonymous with Pterygotus (Pterygotus) by Leif Størmer the same year, and Erettopterus and Acutiramus would be recognized as separate, but closely related, genera (Erettopterus by Erik N. Kjellesvig-Waering in 1961, and Acutiramus by Størmer in 1974).
In 1912, the family Pterygotidae was erected by John Mason Clarke & Rudolf Ruedemann in 1912 to include the eurypterid genera Pterygotus, Slimonia, Hughmilleria and Hastimima. The three latter genera would be reclassified as members of the Hughmilleriidae by Erik N. Kjellesvig-Waering in 1951, leaving Pterygotus and its former subgenera as the sole pterygotid eurypterids.
Pterygotus