| Eurypterid, Buffalopterus, Hughmilleria, Drepanopterus, Stylonurus|
Dolichopterus is a genus of the prehistoric sea scorpions, arthropods in the order Eurypterida.
It lived in the Late Silurian (around 420 million years ago) in shelf or epicontinental seas of the region where Avalonia, Baltica and Laurentia met during the Caledonian orogeny; its fossils have been found in modern-day North America and the Baltic region. They were about 25–30 centimetres (10–12 in) long.
Strobilopterus probably was one of the closest relatives of Dolichopterus, but overall the phylogeny and systematics of the family Dolichopteridae is disputed: some place it closer to the Eurypteridae, while others assign it to the second lineage of sea scorpions which contains the Stylonuridae.
Dolichopteridae, which lived in the Silurian and Devonian periods, had outer surfaces that were either smooth with pustules and semilunar scales. Their compound eyes were arcuate and located anteriorly on the prosoma (head). Their abdomens had epimers (lateral projections). The telson, (tail) was lanceolate. Their chelicerae were small, and the first three pairs of walking lags were stout, with powerful spines. The last pair of walking lags had supplementary lobes, while the swimming lags had the last joint enlarged, as part of the paddle. The male genital appendage was long.
Dolichopterus is distinguishable by its nearly smooth outer surface; its subquadrate prosoma (head), and the slightly serrated margins on the distal joints and lobes of the swimming legs.
The following species have been named:Dolichopterus gotlandicus Kjellesvig-Waering, 1979 – Sweden
Dolichopterus jewetti Caster & Kjellesvig-Waering, 1956 – USA
Dolichopterus macrocheirus Hall, 1859 (type species) – USA, Canada
Dolichopterus siluriceps Clarke & Ruedemann, 1912 – USA, Canada
?Dolichopterus stoermeri Caster & Kjellesvig-Waering, 1956 – Estonia