Diictodon

Diictodon; Temporal range: Capitanian (Guadalupian) – Lopingian (Changhsingian),262–252 Ma PreꞒ Ꞓ O S D C P T J K Pg N
	Adult males with distorted skull
	Undistorted skull of Diictodon in top view (left) and side view (right) scale bar = 1 cm
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Synapsida
Clade:	Therapsida
Suborder:	† Anomodontia
Clade:	† Dicynodontia
Family:	† Pylaecephalidae
Genus:	† Diictodon ; Owen 1876
Species
	D. feliceps (type);
Synonyms
	RhachiocephalodonSeeley, 1898; ? Emydorhynchus Broom, 1913; Pylaecephalusvan Hoepen, 1934; AnomodonKeyser, 1975;

Last updated January 31, 2024

Diictodon is an extinct genus of pylaecephalid dicynodont ^[5] that lived during the Late Permian period, approximately 255 million years ago. Fossils have been found in the Cistecephalus Assemblage Zone of the Madumabisa Mudstone of the Luangwa Basin in Zambia and the Tropidostoma Assemblage Zone of the Teekloof Formation, Tapinocephalus Assemblage Zone of the Abrahamskraal Formation, Dicynodon Assemblage Zone of the Balfour Formation, Cistecephalus Assemblage Zone of the Middleton or Balfour Formation of South Africa and the Guodikeng Formation of China.^[6] Roughly half of all Permian vertebrate specimens found in South Africa are those of Diictodon. This small herbivorous animal was one of the most successful synapsids in the Permian period.^[7]

Characteristics

Appearance

Diictodon had disproportionally large heads that ended in a horny beak. ‘There is a clear distinction between specimens having canine tusks and those lacking them, as tusked specimens are generally larger and more likely to develop a pineal boss. This probably reflects sexual dimorphism, with the tusked sex almost certainly being the male.’ Diictodon had strong arms and legs, as well as 5 sharp claws on each hand, and may have had keen senses of smell and sight. Their gait was similar to the 'high walk' of crocodiles. Their jaws were also simplified, with some of the bones dedicated instead to hearing, considered a key sign of mammalian adaptation. Diictodon also had many adaptations for digging, such as highly developed muscles, a cylindrical body, and wide hands.^[8] Researchers Chinsmay and Rubridge analyzed seven other Dicynodonts species discovering the humerual bone microstructure in Diictidon showed no signs of growth marks indicating a variation in its growth strategy that further improved their ability to dig.^[9]

Lifestyle

As a therapsid, Diictodon shared many features with modern-day mammals. Most noticeably, they made burrows into the earth, but most reached up to 0.5 m (1.6 ft) in depth, suggesting that they might have been infrequent diggers and occupied abandoned burrows.^[8] Still, many scientists believe that Diictodon lived like the modern gopher. Their burrows could have been used to escape the heat of the desert, which was the dominant environment on the continent of Pangaea in the Late Permian Period. Inside these burrows, nests have been found, where Diictodon skeletons are present. They constituted of quite a gregarious lifestyle with numerous burrows in 500 square meters of space. However, their burrows were unconnected and did not form any large colonies. Many Diictodon nested close to flood plains, and some specimens may have been killed as water flowed into the nests, drowning the animals. Diictidon’s primary utilization of humeral excursion rather than forearm extension aided in employing rotation thrusting when burrowing.^[9]Diictodon had no known rival species competing in its niche, so they may have competed primarily with others of their species for the little plant material available.^[8] Fossils of infant Diictodon discovered in brood chambers in some burrows suggest there was parental care in the genus, and that males seem to have been involved in raising the infants, based on the fact that some adults in said burrows had tusks.^[10]

Diet

Like all dicynodonts, Diictodon were herbivorous. They used their beaks to break off pieces of the sparse desert shrubs. Like modern desert animals, Diictodon may have had unusually efficient digestive systems, due to the lack of nutrients present in desert plants. As burrowing animals, they may have fed off of water-rich plant tubers.^[11]

Sexual dimorphism

Previously, tusked individuals were considered males, while tuskless individuals were considered females. Differences in pelvic structure may be the other evidence for sexual dimorphism.^[8]

Phylogeny

Diictodon in a cladogram modified from Angielczyk and Rubidge (2010) showing the phylogenetic relationships of Dicynodontia:^[12]

Related Research Articles

<i>Robertia</i> Extinct genus of dicynodonts

Robertia is an extinct genus of small herbivorous dicynodonts from the Middle to Late Permian of South Africa, between 260 and 265 million years ago. It is a monospecific genus, consisting of the type-species R. broomiana, which was classified by Lieuwe Dirk Boonstra in 1948 and named in honor of Robert Broom for his study of South African mammal-like reptiles.

Cistecephalus is an extinct genus of dicynodont therapsid from the Late Permian of southern Africa. It was a small, specialised, burrowing dicynodont, possibly with habits similar to a modern mole. The head was flattened and wedge-shaped, the body long, and the forelimbs very strong, with similarities in structure to the forelimb of modern burrowing mammals.

<i>Emydops</i> Extinct genus of dicynodonts

Emydops is an extinct genus of dicynodont therapsids from the Middle Permian to Late Permian of what is now South Africa. The genus is generally small and herbivorous, sharing the dicynodont synapomorphy of bearing two tusks. In the following years, the genus grew to include fourteen species. Many of these species were erected on the basis of differences in the teeth and the positioning of the frontal and parietal bones. A 2008 study narrowed Emydops down to two species, E. arctatus and the newly described E. oweni.

The Tapinocephalus Assemblage Zone is a tetrapod assemblage zone or biozone which correlates to the middle Abrahamskraal Formation, Adelaide Subgroup of the Beaufort Group, a fossiliferous and geologically important geological Group of the Karoo Supergroup in South Africa. The thickest outcrops, reaching approximately 2,000 metres (6,600 ft), occur from Merweville and Leeu-Gamka in its southernmost exposures, from Sutherland through to Beaufort West where outcrops start to only be found in the south-east, north of Oudshoorn and Willowmore, reaching up to areas south of Graaff-Reinet. Its northernmost exposures occur around the towns Fraserburg and Victoria West. The Tapinocephalus Assemblage Zone is the second biozone of the Beaufort Group.

The Cistecephalus Assemblage Zone is a tetrapod assemblage zone or biozone found in the Adelaide Subgroup of the Beaufort Group, a majorly fossiliferous and geologically important geological group of the Karoo Supergroup in South Africa. This biozone has outcrops located in the Teekloof Formation north-west of Beaufort West in the Western Cape, in the upper Middleton and lower Balfour Formations respectively from Colesberg of the Northern Cape to east of Graaff-Reinet in the Eastern Cape. The Cistecephalus Assemblage Zone is one of eight biozones found in the Beaufort Group, and is considered to be Late Permian in age.

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Eodicynodon is an extinct genus of dicynodont therapsids, a highly diverse group of herbivorous synapsids that were widespread during the middle-late Permian and early Triassic. As its name suggests, Eodicynodon is the oldest and most primitive dicynodont yet identified, ranging from the middle to late Permian and possessing a mix of ancestral Anomodont/therapsid features and derived dicynodont synapomorphies.

<i>Myosaurus</i> Extinct genus of dicynodont from the lower Triassic

Myosaurus is a genus of Anomodontia in the order Therapsida. They are also classified as Dicynodontia, which is a subclade of Anomodontia. The Mysosaurus was a small, herbivorous synapsid that existed around the early Triassic period. All of the fossils found of this species were found in Antarctica and South Africa. Compared to other fossils found from species that existed during this time, the Myosaurus is not common in the fossil record. This is due to a shortage of discovered fossils that possess characteristics unique to the Myosaurus. Notably, under 130 fossil fragments have been found that have been classified as Myosauridae, and almost all have been skulls. These skulls can be classified as Myosaurus because this species, unlike other dicynodonts, do not possess tusks or postfrontal teeth. The only species identified in the family Myosauridae is the Myosaurus gracilis, or M. gracilis. It should be recognized that the Myosaurus is almost always referred to as the M. gracilis in scientific research.

Brachyprosopus is an extinct genus of dicynodont therapsid from the middle Permian Tapinocephalus Assemblage Zone in the Abrahamskraal Formation belonging to the Beaufort Group of the Karoo Basin, South Africa.

<i>Dicynodontoides</i> Extinct genus of dicynodonts

Dicynodontoides is a genus of small to medium-bodied, herbivorous, emydopoid dicynodonts from the Late Permian. The name Dicynodontoides references its “dicynodont-like” appearance due to the caniniform tusks featured by most members of this infraorder. Kingoria, a junior synonym, has been used more widely in the literature than the more obscure Dicynodontoides, which is similar-sounding to another distantly related genus of dicynodont, Dicynodon. Two species are recognized: D. recurvidens from South Africa, and D. nowacki from Tanzania.

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Koupia is a dubious extinct genus of non-mammalian synapsid. The type species, K. koupensis, was coined by Lieuwe Dirk Boonstra in 1948, with a well-preserved skull from the Tapinocephalus Assemblage Zone of South Africa, SAM-PK-11796, designated the holotype. This specimen has since been lost, and K. koupensis is currently considered a nomen dubium or a possible junior synonym of Brachyprosopus broomi.

<i>Pristerodon</i> Extinct genus of dicynodont therapsid from the late Permian

Pristerodon is an extinct genus of dicynodont therapsid from the Late Permian of South Africa, Zambia and India.

Prosictodon is an extinct genus of pylaecephalid dicynodont from Middle Permian of South Africa. It was first named by Kenneth D. Angielczyk and Bruce S. Rubidge in 2010 and the type species is Prosictodon dubei.

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<span class="mw-page-title-main">Cistecephalidae</span> Extinct family of dicynodonts

Cistecephalidae is an extinct family of dicynodont therapsids from the Late Permian of South Africa, India and Zambia. It includes the genera Cistecephalus, Cistecephaloides, and Kawingasaurus. Cistecephalids are thought to have had a fossorial or burrowing lifestyle, with adaptations such as broad skulls, strong forelimbs, and squat bodies. A similar group of dicynodonts called the pylaecephalids were also fossorial, although to a lesser extent than cistecephalids. Cistecephalids showed a high level of endemism, with each of the five known species unique to a single region.

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References

↑ M.O. Day, B.S. Rubidge; Biostratigraphy of the Tapinocephalus Assemblage Zone (Beaufort Group, Karoo Supergroup), South Africa. South African Journal of Geology 2020;; 123 (2): 149–164. doi: https://doi.org/10.25131/sajg.123.0012
↑ P.A. Viglietti; Biostratigraphy of the Daptocephalus Assemblage Zone (Beaufort Group, Karoo Supergroup), South Africa. South African Journal of Geology 2020;; 123 (2): 191–206. doi: https://doi.org/10.25131/sajg.123.0014
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↑ Angielczyk, K. D., & Sullivan, C. (2008). Diictodon feliceps(Owen, 1876), a dicynodont (Therapsida, Anomodontia) species with a Pangaean distribution. Journal of Vertebrate Paleontology, 28(3), 788–802.
↑ Kammerer, C.F.; Angielczyk, K.D. (2009). "A proposed higher taxonomy of anomodont therapsids" (PDF). Zootaxa. 2018: 1–24.
↑ Diictodon at Fossilworks.org
↑ Sullivan, C., Reisz, R. R., & Smith, R. M. H. (2003). The Permian mammal-like herbivoreDiictodon, the oldest known example of sexually dimorphic armament. Proceedings of the Royal Society of London. Series B: Biological Sciences, 270(1511), 173–178. https://doi.org/10.1098/rspb.2002.2189.
1 2 3 4 Ray, S., & Chinsamy, A. (2003). Functional aspects of the postcranial anatomy of the Permian dicynodont Diictodon and their ecological implications. Palaeontology, 46(1), 151–183. https://doi.org/10.1111/1475-4983.00292.
1 2 Ray, Sanghamitra; Chinsamy, Anusuya (2004-03-25). "Diictodon feliceps (Therapsida, Dicynodontia): bone histology, growth, and biomechanics". Journal of Vertebrate Paleontology. 24 (1): 180–194. Bibcode:2004JVPal..24..180R. doi:10.1671/1914-14. ISSN 0272-4634. S2CID 86189707.
↑ Smith, Roger M. H.; Angielczyk, Kenneth D.; Benoit, Julien; Fernandez, Vincent (1 May 2021). "Neonate aggregation in the Permian dicynodont Diictodon (Therapsida, Anomodontia): Evidence for a reproductive function for burrows?". Palaeogeography, Palaeoclimatology, Palaeoecology. 569: 110311. Bibcode:2021PPP...56910311S. doi:10.1016/j.palaeo.2021.110311. S2CID 233585323.
↑ Cox, C. B. (1998). The jaw function and adaptive radiation of the dicynodont mammal-like reptiles of the Karoo basin of South Africa. Zoological Journal of the Linnean Society, 122(1-2), 349–384. https://doi.org/10.1111/j.1096-3642.1998.tb02534.x
↑ Kenneth D. Angielczyk; Bruce S. Rubidge (2010). "A new pylaecephalid dicynodont (Therapsida, Anomodontia) from the Tapinocephalus Assemblage Zone, Karoo Basin, Middle Permian of South Africa". Journal of Vertebrate Paleontology. 30 (5): 1396–1409. Bibcode:2010JVPal..30.1396A. doi:10.1080/02724634.2010.501447. S2CID 129846697.