Trochorhinus
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| Trochorhinus Temporal range: Middle Permian, | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Synapsida |
| Clade: | Therapsida |
| Clade: | †Therocephalia |
| Family: | †Lycosuchidae |
| Genus: | †Trochorhinus Broom, 1936 Nomen dubium |
| Species: | †T. vanhoepeni |
| Binomial name | |
| †Trochorhinus vanhoepeni Broom, 1936 Nomen dubium (=Lycosuchidae incertae sedis) | |
Trochorhinus is a dubious genus of therocephalian therapsid from the middle Permian (Capitanian) of South Africa based on a badly weathered and undiagnostic fossil of a lycosuchid therocephalian. It includes the type and only species, T. vanhoepeni, and was named by Scottish-born South African palaeontologist Robert Broom in 1936.[1] Trochorhinus is identifiable as a member of Lycosuchidae by only having five upper incisors in each premaxilla, but the specimen is otherwise too poorly preserved and undiagnostic to determine its affinity beyond this family. As such, Trochorhinus is considered to be a nomen dubium and the only known specimen to represent Lycosuchidae incertae sedis.[2]
Trochorhinus was named for a specimen of a badly weathered lycosuchid snout and an associated lower jaw fragment. Like some other lycosuchids, two similarly sized large simulatenously erupted "double canines" are present in at least the left maxilla, though only the second canine and the root of the first present in the corresponding right maxilla.[3][a] Broom named Trochorhinus as a new genus on the basis of differences in its teeth compared to Trochosaurus, with the five incisors of Trochorhinus measuring only 35 mm compared to 45 mm and 48 mm in Trochosaurus major and T. intermedius, respectively. As the skull comes from a large individual, Broom concluded that this difference could not be attributed to differences in age and growth (ontogeny) and therefore that it represented a distinct genus. He further justified its distinction by identifying only three upper and four lower postcanine teeth in each side of the jaw, one less in each than in Trochosaurus.[1][2]
The holotype specimen, TM 275, was collected by Dutch-born South African paleontologist Egbert Cornelis Nicolaas van Hoepen from the Abrahamskraal 29 farm in Prince Albert, South Africa, in deposits of the middle-Permian aged Tapinocephalus Assemblage Zone of the Abrahamskraal Formation.[2][3] Notably, this locality is one of the stratigraphically lowest (and so the oldest) where lycosuchid fossils have been found, making TM 275 (alongside the holotype of Trochosaurus intermedius) one of the oldest recognised lycosuchid specimens known, older than the known lower ranges of both the valid lycosuchids Lycosuchus and Simorhinella. Also, although the specimen is too poorly preserved for measurements of the whole snout or skull to be made or even estimated, the distance between the tip of the snout and the last incisor suggests it comes from an individual on the larger end of the known size range of lycosuchids (comparable in proportions to large specimens referred to another dubious lycosuchid, Scymnosaurus ferox).[3]
