Moschorhinus
Genus of synapsid from late Permian and early Triassic South Africa
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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 Early Triassic of the South African Karoo Supergroup. It was a large carnivorous therapsid, reaching 1.1–1.5 metres (3.6–4.9 ft) 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 likely an apex predator.
| Moschorhinus | |
|---|---|
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| Restoration of Moschorhinus kitchingi | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Synapsida |
| Clade: | Therapsida |
| Clade: | †Therocephalia |
| Family: | †Akidnognathidae |
| Genus: | †Moschorhinus Broom, 1920 |
| Species: | †M. kitchingi |
| Binomial name | |
| †Moschorhinus kitchingi Broom, 1920 | |
| Synonyms | |
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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. Following its extinction, the large synapsid carnivore niche was later filled by 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.[2]
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.[2] It is now one of the best known and most recognizable therapsids of the supergroup.[3]
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.[1]
Moschorhinus remains have been found most prominently in the Upper Permian to Lower Triassic Beaufort Group.[3][4][5]
Classification
Moschorhinus is a therocephalian, a member of the clade Eutheriodontia and the sister taxon to cynodonts and modern mammals.[6] Moschorhinus is classified into the family Akidnognathidae, along with other large, carnivorous therapsids with strong skulls and large upper canines.[7]
Description
Size
Moschorhinus was a large therocephalian, reaching 1.1–1.5 metres (3.6–4.9 ft) in total body length.[8][9] NMQR 3351, a specimen with a skull length of 240 mm (9.4 in), was estimated to have weighed 84.3 kilograms (186 lb).[9] Permian specimens were larger than Triassic specimens, with Permian skulls averaging 207 mm (8.1 in) in length, while that of Triassic skull averaged 179 mm (7.0 in).[3]
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.[7][4] The lower jaw is much broader than that of any other therocephalian.[7][4] The upper snout projects a bit beyond the incisors in juveniles.[4] The nostrils were large and positioned towards the tip of the snout.[4]
The palate is convex, with a broad, triangular vomer, with paired tubercles, rounded projections pointing ventrally,[7][4] similar to other akidnognathids.[2] 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.[7]
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.[10]
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.[2][4] 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.[11]
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.[2] The jugal ends at the eye socket, and is not convex, as in several later therocephalians.[4]
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.[2] 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.[4] 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).[7]
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.[4][10]
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.[9]
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.[9]
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).[3][12][4]
Predatory behavior
Following the extinction of basal therocephalians (lycosuchids and scylacosaurids), eutherocephalians were predominantly small-bodied and were likely insectivores. However, a eutherocephalians such as Moschorhinus were able to re-evolved large body sizes and macropredatory behavior.[13] 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.[7]
Paleoecology
Daptocephalus Assemblage Zone
Moschorhinus first appeared in the Lystrosaurus maccaigi-Moschorhinus subzone of the Daptocephalus Assemblage Zone.[14] Ash-fall deposits suggests the subzone dates between 253.48 ± 0.15 to 252.24 ± 0.11.[15][14] Contemporary therapsids included dicynodonts such as Dicyodon lacerticeps, Diictodon feliceps, 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.[16][14] Sauropsids were represented by the pareiasaur Pareiasaurus serridens, the owenettid Owenetta rubidgei, and Spondylolesyes rubidgei, with amphibians including rhinesuchid temnospondyls Rhinesuchus and Uranpcentrodon senekalensis.[14] Moschorhinus was able to coexist with the smaller gorgonopsians due to its robust cranial and postcranial traits, additionally its fast growth may have given it a competitive advantage over the similar sized gorgonopsians.[9]
The Lystrosaurus maccaigi-Moschorhinus subzone had notable changes in the fauna compared to the Dicynodon-Theriognathus subzone. Rubidgeines died out early within the assemblage zone, with only Rubidgea surviving to the boundary before going extinct during a turnover event that separated the two subzones. The turnover event also saw the extinction of dicynodonts such as Aulacephalodon baini. Following their extinction, they were replaced by the Laurasian Inostrancevia.[16] Additionally, the whaitsiid Theriognathus was absent from the upper proportion of the assemblage zone, being replaced by Moschorhinus.[17]
The end of the assemblage zone coincided with the Permian-Triassic mass extinction, which saw the extinction of gorgonopsians, pareisaurs, and most dicynodonts.[3][18][19][16] Moschorhinus would survive the extinction event and ecologically replace the gorgonopsians and were the largest predators in the fauna after their extinction.[16][7]
Lystrosaurus Assemblage Zone
The Lystrosaurus Assemblage Zone is marked by the appearance of Lystrosaurus declivis and Lystrosaurus murrayi. New sauropsids represented by the archosauriforms Proterosuchus fergusi, Prolacerta broomi, Heleosuchus griesbachi and Noteosuchus colletti, the lepidosauromorpha Paliguana white, parareptiles Saurodektes kitchingorum, Coletta seca, Procolophon trigoniceps, Sauropareion anoplus, and Phonodus dutoitorum. Appearance of Triassic therapsids were represented by dicynodont Lsytrosaurus and Myosaurus gracilis, therocephalians Olivierosuchus parringtoni, Regisaurus jacobi, Scaloposaurus constrictus, Tetracynodon darti, and Ericiolacerta parva, and cynodonts Platycraniellus elegans, Progalesaurus lootsbergensis, Galesaurus planiceps, Thrinaxodon liorhinus. Amphibians were represented by temnospondyls such as Rhytidosteus capensis, Broomistega putterilli, Micropholis stowi, Thabanchuia oomie, Lydekkerina huxleyi, Eolydekkerina magna, Kestrosaurus dreyeri, and an indeterminate Trematosauridae.[20] Compared to Permian Moschorhinus, Triassic Moschorhinus were smaller than the former, likely in response to the harsher conditions of the Early Triassic. Despite the decrease in size, Moschorhinus was still the largest therocephalian of the Triassic.[3][21][4]
Extinction
Moschorhinus would extinct in the Early Triassic after the Permian Extinction as the result of the second wave of extinction,[22][23][24][25] along with 80–95% of animal species, due to a mass hypoxia event. This appears to have led to stunted growth,[3] intense seasons, reduced ecosystem diversity, and a loss of forests.[4] Following the extinction of Moschorhinus by the Triassic, the large carnivorous synapsid niche was filled by cynodonts such as Cynognathus.[7]