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Moschorhinus is an extinct genus of synapsid in the family Akidnognathidae with only one species: M. kitchingi, which has been found in the Late Permian to Early Triassic of the South African Karoo Supergroup. It was a large carnivorous therapsid, reaching in total body length with the largest skull comparable to that of a lion in size, and had a broad, blunt snout which bore long, straight canines.
Moschorhinus appears to have ecologically replaced the as an apex predator, and hunted much like a big cat. While most abundant in the Late Permian, it survived into the Early Triassic in small numbers after the Permian Extinction, though these Triassic survivors had stunted growth.
Kitching discovered the holotype specimen, a skull (best preserved, the palate), in the Karoo Supergroup in South Africa, near the village of Nieu-Bethesda. It was first described by paleontologist Robert Broom in 1920. It is now one of the best known and most recognizable of the supergroup.
Broom had previously named another species of therocephalian in 1907 from KwaZulu-Natal, Scymnosaurus warreni, that he later moved to Moschorhinus in 1932 as M. warreni, maintaining it as a distinct species. M. warreni was later recognised as a probable synonym of M. kitchingi by Kitching in his unpublished PhD thesis, and a re-description of the holotype in 2023 by David Groenewald and Christian Kammerer confirmed this proposal. As the older name, M. warreni would have taxonomic priority over M. kitchingi for the species. However, Groenewald and Kammerer (2023) believed it would be premature to establish M. warreni as the correct name, pending a revision of akidnognathid therocephalian taxonomy and the possibility that even older names may have seniority.
Moschorhinus remains have been found most prominently in the Upper Permian to Lower Triassic Beaufort Group.
Moschorhinus took over the ecological niche once controlled by . Both groups were built much like . Following the extinction of Moschorhinus by the Triassic, took over a similar niche.
Lateral view of Moschorhinus jaw, showing range of motion necessary for such large incisors, and upper palatal fenestrae of snout. (From van Valkenburgh and Jenkins, 2002).
The nostrils were large and positioned towards the tip of the snout.
The incisors are housed in the . They are large, curve slightly, and have a bell-shaped cross-section. They had smooth cutting surfaces, and, unlike those of other therocephalians, lacked facets or striae resulting from abrasion and wear.
The large saber-like canines are held within the , and are quickly identifiable features of Moschorhinus. They are especially thick and strong, and uniquely circular in cross-section. In length, these sabers are comparable to gorgonopsids. While there is no real modern analogue, the most similar living example would be the clouded leopard ( Neofelis nebulosa).
Like other therocephalians, Moschorhinus had a reduced number of postcanines which were housed in the maxillae. In most therocephalians, the “teeth,” or rather toothlike projection (denticulations) of the , are greatly reduced or missing, and in Moschorhinus they are absent.
The sabers require the mouth to open widely for use, making feeding difficult. The closely related Promoschorhynchus shows stiff folds ( crest) on the border of the nasal passage and the throat, used to keep it open and to allow for breathing while eating. The development of a secondary palate in the skull gradually evolved in therocephalians, and the choanal crest is featured in all later therocephalians.
Moschorhinus seems to have gone extinct in the Early Triassic at 251 mya after the Permian Extinction by 252 mya, along with 80–95% of animal species, due to a mass hypoxia event. This appears to have led to stunted growth, intense seasons, reduced ecosystem diversity, and a loss of forests. Fossil evidence shows that Triassic Moschorhinus grew faster than Permian ones, resulting in reduced body size in the former, largely believed to be an effect of the harsher environmental variability after the Permian Extinction (Lilliput effect). Permian skulls average in length, while that of Triassic skull is only . Nonetheless, Triassic Moschorhinus were the largest therocephalians of their time.
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