Heleosuchus
Heleosuchus is an extinct genus of diapsid reptile from the Late Permian of South Africa. It was originally described as a species of "Saurosternon", but was later recognized as a separate taxon by Robert Broom. At one time, the type specimen of "Heleosuchus", was thought to be lost. However, it remains at the Natural History Museum (formerly British Museum (Natural History)), where it is numbered 2374, and a cast R. 5000. Several other casts of Natural History Museum specimen 2374 are present in several other European institutions, among them a cast of higher fidelity to the original, the whereabouts  of which are unknown. While the type was thought to be lost, S. E. Evans redescribed this taxon on the basis of an older mold which had been taken of the type specimen prior to its disappearance. When the specimen appeared in later years, a higher quality mold was taken and described by R. L. Carroll that allowed a better description of this taxon. "Heleosuchus" is only known from the posterior half of the skull and a cervicodorsal column with some associated forearm elements and hind limb elements. The hind limbs are better preserved than the forearms. "Heleosuchus" is suggested  as being either an early diapsid reptile, not closely related to other lineages, or as being an aberrant and primitive lepidosauromorph. "Heleosuchus" shares the hooked fifth metatarsal found in some other diapsids, such as primitive turtles ("Odontochelys"), lepidosauromorphs, and archosauromorphs, but it also resembles "younginiform"-grade diapsids in its gross morphology. "Heleosuchus" may also share a thyroid fenestra with these higher diapsid reptiles as well, but the identity of this feature is disputed.