A third species, "Sphenacodon britannicus", has sometimes been cited in the literature. In 1908 German paleontologist F. von Huene described "Oxyodon britannicus", based on part of a maxilla found in England, (The generic name "Oxyodon" is preoccupied by a fish ("Oxyodon" Baur, 1906) and so is invalid.) The specimen had been identified earlier as a possible Triassic dinosaur, but von Huene recognized a "pelycosaur." Paton transferred the species to "Sphenacodon" in 1974, noting it would have been an animal about the size of "Sphenacodon ferox". However, more recent studies have questioned whether such limited fossil material can be used to distinguish between "Dimetrodon" and "Sphenacodon"—or its own genus. The species ""Oxyodon"" "britannicus" (or as "Sphenacodon" (?) "britannicus") is now generally classified as Sphenacodontidae "incertae sedis" (of uncertain placement).