Scymnosaurus

Scymnosaurus is a dubious genus of therocephalian therapsids from the Middle Permian of what is now South Africa based upon the fossils of large, but indeterminate, early therocephalians. The genus and its type species S. ferox was named by Robert Broom in 1903, followed by S. watsoni in 1915. A third species, S. major, was named by Lieuwe Dirk Boonstra in 1954, who also referred many more specimens to the genus as Scymnosaurus sp.

The genus Scymnosaurus and its species are all considered nomina dubia today, meaning the fossils have no distinguishing (diagnostic) traits to define each species or to unite them together as a distinct genus. Indeed, Scymnosaurus includes specimens that have since been determined to belong to two separate families of carnivorous early therocephalians. Most specimens, including those of S. ferox and S. major, represent indeterminate (incertae sedis) specimens from the family Lycosuchidae, while the sole skull of S. watsoni belongs to an indeterminate member of Scylacosauridae. Though Scymnosaurus watsoni represents a scylacosaurid, because the type species S. ferox is identifiable as a lycosuchid, the genus Scymnosaurus itself is regarded as a dubious lycosuchid.

Most specimens attributed to Scymnosaurus are fragmentary, often only partial snouts and jaws. The genus was originally defined in part upon a specific shared tooth count, which is now known to be unreliable for diagnosing early therocephalians and the same dental formula is now known to be typical of lycosuchids in general. The only other consistent feature to unite these fossils is their large size, and though not diagnostic, they notably include some of the largest known specimens of any therocephalians, with the largest specimens representing skulls estimated to exceed 40 cm (16 in) in length.