Species in this genus are traditionally classed into two skull groups: longirostrine (long, narrow jaws) and brevirostrine (short, broad jaws).
A 2005 phylogenetic analysis into the evolutionary relationships of Thalattosuchia did not support the monophyly of Steneosaurus, as the genera Machimosaurus and Teleosaurus both fell within Steneosaurus. Reinforcing the paraphyly of Steneosaurus, the Callovian species "Steneosaurus" obtusidens has been recovered as the sister species of Machimosaurus in recent cladistic analyses of Thalattosuchia and renamed Lemmysuchus, while Steneosaurus bollensis was recovered in a basal position to other members of Steneosaurus sensu lato. Given the paraphyly of Steneosaurus, Macrospondylus von Meyer, 1830 is the earliest available generic name for S. bollensis.
From the semi-aquatic Oker locality in Lower Saxony, Germany (Kimmeridgian-age) two genera of teleosaurids (Steneosaurus and Machimosaurus) are known, in addition to the neosuchian genera Goniopholis and Knoetschkesuchus.