Moschorhinus

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Moschorhinus
Temporal range:
Ma
↓
Restoration of Moschorhinus kitchingi
Scientific classification Edit this classification
Domain: Eukaryota
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

Moschorhinus is an

canines
.

Moschorhinus appears to have ecologically replaced the

Permian Extinction, though these Triassic survivors had stunted growth
.

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

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 M. warreni was later recognised as a probable synonym of M. kitchingi by Kitching in his unpublished PhD thesis, and a re-description of the holotype in 2023 by David Groenewald and Christian Kammerer confirmed this proposal.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]

The Karoo Supergroup and its outcrops

Moschorhinus remains have been found most prominently in the

Lower Triassic Beaufort Group.[3][4][5]

Classification

Moschorhinus is a

cynodonts and modern mammals. Moschorhinus is classified into the family Akidnognathidae, along with other large, carnivorous therapsids with strong skulls and large upper canines.[6]

Moschorhinus took over the

cynodonts took over a similar niche.[6]

Description

Side view of the head, showing the sabers and range of motion for the jaw

Moschorhinus was a large carnivore, reaching 1.5 m (4.9 ft) in total body length.

saber toothed cats.[6][8]

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).[6]

Snout

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.[6][4] The lower jaw is much broader than that of any other therocephalian.[6][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]

Teeth

Moschorhinus is thought to have had a

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 saber-like canines are held within the maxillae, 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).[6]

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][9]

Skull roof

Tracing the roof of the skull, Moschorhinus possesses small

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.[10]

Eye sockets

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]

Palate

Overall, the palate is convex, with a broad, triangular vomer, with paired tubercles, rounded projections pointing ventrally,[6][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.[6]

The sabers require the mouth to open widely for use, making feeding difficult. 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.[9]

Paleobiology

Reconstruction feeding on a Lystrosaurus

It is presumed that Moschorhinus was a cat-like predator, being able to pierce skin and hold onto struggling prey with its long canines. This is the first record of this kind of hunting technique. Given its sturdily designed, thick snout, enormous canines, and powerful jaw muscles, Moschorhinus appears to have been a daunting predator.[6]

Paleoecology

Many vertebrate fossils have been uncovered in the Karoo Basin. Other therocephalians from the same rock level are Tetracynodon and Promoschorhynchus.[3] Moschorhinus specimens were the only large therocephalians.[11][4]

Moschorhinus seems to have gone extinct in the Early Triassic at 251 mya after the

Permian Extinction by 252 mya,[12][13][14] 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] 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][15][4] Permian skulls average 207 mm (8.1 in) in length, while that of Triassic skull is only 179 mm (7.0 in).[3] Nonetheless, Triassic Moschorhinus were the largest therocephalians of their time.[3][11]

References

  1. ^
    hdl:10539/37143
    .
  2. ^ a b c d e f Broom R (1920). "On Some New Therocephalian Reptiles from the Karroo Beds of South Africa". Proceedings of the Zoological Society of London: 351–354.
  3. ^
    S2CID 86490421
    .
  4. ^ a b c d e f g h i j k l m Huttenlocker, Adam (2013). The Paleobiology of South African Therocephalian Therapsids (Amniota, Synapsida) and the Effects of the End-Permian Extinction on Size, Growth, and Bone Microstructure (Ph.D). University of Washington.
  5. doi:10.1146/annurev.ecolsys.32.081501.114113
    .
  6. ^
    doi:10.1017/S1089332600001121. Archived from the original
    (PDF) on 2013-10-17.
  7. doi:10.1111/j.1502-3931.2007.00011.x. Full version online at "Lystrosaurus species composition across the Permo–Triassic boundary in the Karoo Basin of South Africa" (PDF). Archived from the original
    (PDF) on 2008-09-10. Retrieved 2008-07-02.
  8. S2CID 84603632. Archived
    (PDF) from the original on 19 Mar 2023.
  9. ^
    doi:10.1111/j.1439-0469.1996.tb00805.x
    .
  10. ^ Durand J F (1991). "A revised descripction of the skull of moschorhinus (therapsida, therocephalia)". Annals of the South African Museum. 99: 381–413.
  11. ^
    S2CID 128981733
    .
  12. S2CID 46198018
    .
  13. doi:10.1016/j.jafrearsci.2006.04.006. [dead link
    ]
  14. PMID 12965004
    .
  15. doi:10.1016/j.palaeo.2006.11.038
    .
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