Heleophilus is an extinct genus of early stem-reptile known from the Permian of South Africa. The genus contains a single species, Heleophilus acutus, known from a skull and partial skeleton described in 1909. The locality these remains were collected from likely belongs to the mid–upper Permian Endothiodon Assemblage Zone, though this is unclear and has been debated. Various authors have interpreted the remains as similar to Heleosaurus and Broomia, or as a member of the Younginidae, though the most recent summary tentatively placed it within the family Millerettidae. The skull of Heleophilus is short and tapering, bearing long, pointed teeth.
History and identity
The Heleophilus fossil material was discovered by the British-South African paleontologist and medical doctor Robert Broom in Victoria West, South Africa. The specimen consists of a small, crushed skull including the mandible, a poorly preserved portion of the neck, and part of the foot. In 1909, Broom described these fossil remains as belonging to a new genus and species, which he named Heleophilus acutus. Broom provided a brief description of the fossils without figuring them. He regarded it as "impossible to be certain" of its affinities, but considered Heleophilus to be a close relative of Heleosaurus with "typically Diaptosaurian" features, and placed both genera within the Mesosauria. Based on discussion with South African geologist A. L. du Toit, who had visited the type locality, Broom decided that the rock outcrops at Victoria West are very low in the Beaufort Group and could likely be dated to the lower to middle Permian. In a documentation that year of the vertebrate fossils in South Africa's Karoo Basin, Broom tentatively placed Heleophilus alongside Heleosaurus in the supergroup's "Pareiasaurus Beds". Both genera were maintained as relatives of Mesosaurus, but with "much less typically aquatic forms." In 1912, German paleontologist Friedrich von Huene briefly argued that Mesosaurus was not a close relative of Heleophilus and Heleosaurus, leaving the latter genera within the broader group Cotylosauria. This was followed by American researcher S. W. Williston later that year, who claimed that the traditional use of the name Mesosauria "has no legitimate standing."
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