Moschorhinus is an extinct genus of therocephalian synapsid in the family Akidnognathidae with only one species: M. kitchingi, which has been found in the Late Permian to Earliest 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. These adaptations suggested it hunted much like a felid and was a functioned as a mesocarnivore within the upper subzone of the Daptocephalus Assemblage Zone.
While most abundant in the Late Permian, it survived into the Early Triassic in small numbers after the Late Permian Extinction, though these Triassic survivors had stunted growth. Following the extinction event, Moschorhinus ecologically replaced the gorgonopsians as the largest predator in the assemblage prior to the arrival of archosauriforms. Moschorhinus would go extinct 160,000 years after the first wave of extinctions, being replaced by archosauriforms and cynodonts.
Taxonomy The genus name Moschorhinus is derived from the Ancient Greek words μόσχος (mos'-khos) moschos for calf or young animal, and rhin/rhino- for nose or snout, in reference to its short, broad snout. The species name, kitchingi, refers to Mr. James Kitching, who originally found (but did not describe) the specimen.
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 therapsids 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 M. warreni was later recognised as a probable synonym of M. kitchingi by Kitching in his unpublished PhD thesis, and a re-description of the holotype in 2023 by David Groenewald and Christian Kammerer confirmed this proposal.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.
Classification Moschorhinus is a therocephalian, a member of the clade Eutheriodontia and the sister taxon to cynodonts and modern mammals. Moschorhinus is classified into the family Akidnognathidae, along with other large, carnivorous therapsids with strong skulls and large upper canines.
Description
Size Moschorhinus was a large therocephalian, reaching in total body length. Full version online at NMQR 3351, a specimen with a skull length of , was estimated to have weighed . Permian specimens were larger than Triassic specimens, with Permian skulls averaging in length, while that of Triassic skull averaged .
Skull The skull is similar to that of the gorgonopsians, with large temporal fenestrae (three in total as a synapsid) and a convexly bowed palate. The snout of Moschorhinus is characteristically short and broad. The blunt tip of the snout features a ridge running down the midline to the frontal bone. The lower jaw is much broader than that of any other therocephalian. The upper snout projects a bit beyond the incisors in juveniles. The nostrils were large and positioned towards the tip of the snout.
The palate is convex, with a broad, triangular vomer, with paired tubercles, rounded projections pointing ventrally, similar to other akidnognathids. The palatine bones (forming the back of the roof of the mouth) are enlarged and thick, especially on their outer edges where they are joined to the maxilla. On their inner edges, the palatines are joined to the pterygoid and vomer on the nose, forming part of the circumference of the nasal cavity. Between the palatine and maxilla, just behind the canines, are large foramens, presumably to allow for nerves. A slanting ridge along the middle of the palatine presumably supported a soft palate, which allowed air to travel between the nose and the lungs.
The closely related Promoschorhynchus shows stiff folds (choanal 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.
Tracing the roof of the skull, Moschorhinus possesses small prefrontal bones above the eyes, followed by large, widened frontal bones. The parietals form a narrow sagittal crest along the midline of the skull, which houses a very basic pineal foramen. Indentations can be seen in the temporal fossae, depressions on either side of the crest, indicating the presence of many blood vessels and nerves supplying the brain.
The lacrimal bone is larger than the reduced prefrontal, and forms the majority of the eye socket. The lacrimal has a bony boss (a rounded knob) on the orbit, and a large foramen towards its inner side. The lower edge of the eye socket is formed the jugal and maxillary bones. The jugal ends at the eye socket, and is not convex, as in several later therocephalians.
Dentition Moschorhinus is thought to have had a dental formula of I6.C1.M3, with 6 incisors, 1 canine, and 3 postcanines in either side of the upper jaw. The incisors are housed in the premaxillae. 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 canines are held within the maxillae, and are quickly identifiable features of Moschorhinus. In length, these canines were comparable to gorgonopsians, although they were more round in the cross-section. 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 pterygoid bones, are greatly reduced or missing, and in Moschorhinus they are absent.
Postcranial remains Moschorhinus had a presacral vertebral count of 27, which is consistent with other therocephalians, which suggests compared to other therapsid clades, therocephalians had a highly conversed number of presacral vertebrae. The axial skeleton of Moschorhinus has remarkable similarities to Scaloposaurus along with differentiation, along with morphological changes in the ribs and vertebral structures in the transitional region. The seventh cervical vertebrae is noted to have been a transition to the dorsal region with the projection of the neural spine becoming more dorsal, the neural arch having an absence of the lateral ridge on the lateral margin, and an increase in the anteroposterior width. The ribs of the seventh cervical is more anteroposteriorly broader than preceding cervical ribs and nearly equal to succeeding dorsal ribs in length.
The scapula of Moschorhinus was similar to that of other therocephalians by having an elongated scapular blade, a convex lateral surface, and lacking an acromion process. Compared to other eutherocephalians, the scapula of Moschorhinus and other akidnognathids were generally more robust. The humerus was more similar to basal therocephalians in the degree of its robustness and expansion of the epiphyses, compared to the comparatively narrow epiphyses of eutherocephalians. However, compared to basal therocephalians, the humerus supported a large, well-developed deltopectoral crest and lacked a ectepicondylar foramen. The radius and ulna were noted to have been relatively similar to other therocephalians.
Paleobiology
Growth 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).
Predatory behavior Following the extinction of basal therocephalians (lycosuchids and scylacosaurids), eutherocephalians were predominantly small-bodied and were likely insectivores. However, some eutherocephalians such as Moschorhinus were able to re-evolved large body sizes and macropredatory behavior. Valkenburgh and Jenkins (2002) hypothesized the combination of long, robust canines and flattened incisors suggests Moschorhinus was a cat-like predator, being able to pierce skin and hold onto struggling prey with its long canines.
Paleoecology
Daptocephalus Assemblage Zone Moschorhinus first appeared in the Lystrosaurus maccaigi-Moschorhinus subzone of the Daptocephalus Assemblage Zone. Ash-fall deposits suggests the subzone dates between 253.48 ± 0.15 to 252.24 ± 0.11. The upper subzone was thought to have been a well-drained floodplain. The Lystrosaurus maccaigi-Moschorhinus subzone had notable changes in the environment compared to the older Dicynodon-Theriognathus subzone, with an increase in aridification, which saw the decline of lacustrine floodplains, which were replaced by well-drained floodplains. During the transition, gorgonopsians, such as rubidgeines and Lyaencops went extinct. Following the extinction of the rubidgeines, the Laurasian Inostrancevia filled in the vacant niche as the apex predator. Additionally, the whaitsiid Theriognathus also went extinct during the transition, being replaced by Moschorhinus. The turnover event also saw a notable extinctions among dicynodonts such as Diictodon feliceps and Aulacephalodon bainii. It also saw the first appearance of Lystrosaurus maccaigi, which became increasing abundant following the end of the transition.
Contemporary therapsids included dicynodonts such as Dicyodon lacerticeps, Dinanomodon gilli, Daptocephalus leoniceps, Pelanomodon moschops, and Lystrosaurus, therocephalians such as Lycideops longcips, Nanictidops kitchingi, Promoschorhynchus, and Polycynodon elegans, cynodonts such as Cynosaurus suppostus, Nanictosaurus kitchingi, and Vetusodon elikhulu, the biarmosuchian Ictidorhinus matinsi, and gorgonopsians such as Cyonosaurus longiceps, Arcognathus curvimola, and Inostrancevia africana. Sauropsids were represented by the pareiasaur Pareiasaurus serridens, the owenettid Owenetta rubidgei, and Spondylolesyes rubidgei, with amphibians including rhinesuchid temnospondyls Rhinesuchus and Uranpcentrodon senekalensis.
The presence of similar sized predators within the mesocarnivorous niche suggests some form of niche partitioning was present. Moschorhinus had more robust forelimbs than the small-bodied gorgonopsians, which were more gracile in comparison. Its metacarpals and phalanges were shorter compared to the stylopod and zeugopod. In comparison, gorgonopsians had longer and larger metacarpals and phalanges, which suggests a different lifestyle and ecological niche between small-bodied gorgonopsians and Moschorhinus. The anatomy of their canines were also different, with the conical canines of Moschorhinus being adapted for withstanding, while the blade-like canines of gorgonopsians was better suited for slashing, as well as "puncture and pull" biting. The combination of its robust cranial and postcranial anatomy, as well as its rapid and consistent growth may have given it a competitive advantage over the similar sized gorgonopsians.