Stylonurine eurypterids comprise a monophyletic suborder of aquatic chelicerates known from marine, brackish and freshwater environments through the late Ordovician to end Permian. Compared to the nektonic predatory Eurypterina the relationships of the Stylonurina are poorly known, with current phylogenetic analyses unable to resolve the topology of the various familial clades. Restudy of the genus Drepanopterus has shown it to be polyphyletic, with Drepanopterus sensu stricto being a primitive sweep-feeding hibbertopteroid and several Silurian species appearing to be basal members of the Eurypterina. Including this new data in a phylogenetic analysis of the suborder results in a well-resolved tree showing that hibbertopterids, formerly considered to be a separate order to Eurypterida, clade within Stylonurina and that a sweep-feeding lifestyle evolved twice independently within the suborder. It is also apparent that Stylonurina remained relatively unaffected by the drastic decline in Eurypterina diversity during the Early Devonian; macroevolutionary analysis of maximum size and diversity across the whole of Eurypterida suggests that competition with early jawed vertebrates and other predators may have been the cause of the gigantism and pattern of extinction seen in Eurypterina, while Stylonurina adopted a non-competitive strategy that allowed them to survive into the Permian.