Biology:Dinocephalia

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Dinocephalia is a clade of generally large-bodied therapsids that flourished during Middle Permian between approximately 275 and 260 million years ago (Ma),[1][2][3] but became extinct during the Capitanian mass extinction event. Dinocephalians included herbivorous, carnivorous, and omnivorous forms.[4] Many species had thickened skulls with many knobs and bony projections. Dinocephalians were the first non-mammalian therapsids to be scientifically described[5] and their fossils are known from Russia, China, Brazil, South Africa, Zimbabwe, and Tanzania.[6][7]

Description

They include carnivorous, herbivorous, and omnivorous forms. It has been disputed as to whether some dinocephalians were semi-aquatic like hippopotamuses.[8]

Size

Size of various individuals of the large carnivorous dinocephalian Anteosaurus compared to a human
Size of the herbivorous or omnivorous dinocephalian Jonkeria compared to a human

Dinocephalians were generally large in size,[1] and some the largest animals of the Permian period, and the first synapsids to reach a body size around one tonne.[9] The herbivorous or omnivorous Jonkeria has been suggested to have weighed 989 kilograms (2,180 lb), while the large carnivore Anteosaurus has been estimated to weigh 400 kilograms (880 lb) based on scaled 3D models.[10]

Skull and jaws

Cranial ornamentation in dinocephalians
Skull of Titanophoneus (Anteosauria)
Skull of Moschops (Tapinocephalidae)
Skull of Estemmenosuchus

The temporal fenestra at the back of the skull is relatively enlarged in dinocephalians,[11]11 with the quadrate and quadratojugal bones at the back of the skull also being enlarged.[11]38 The premaxillary bones at the front of the snout unusually among therapsids have a long posteriorly directed spur-like process between the paired nasal bones, which in some dinocephalians causes the nasal bones to not contact each other, due the premaxillae reaching all the way to the frontal bones. The septomaxilla (a skull bone associated with the nostril opening) generally has a small exposure on the skull surface. There is no preparietal bone unlike some other therapsids. The prefrontal and lacrimal bones are generally large and form part of the border of the orbit (eye socket).[11]38

All dinocephalians are characterised by the interlocking incisor (front) teeth, though this was formerly thought to be unique to the group, it is also found in biarmosuchians.[12] Correlated features are the distinctly downturned facial region, a deep temporal region, and forwardly rotated suspensorium. Shearing contact between the upper and lower teeth (allowing food to be more easily sliced into small bits for digestion) is achieved through keeping a fixed quadrate and a hinge-like movement at the jaw articulation. The lower teeth are inclined forward, and occlusion is achieved by the interlocking of the incisors. The later dinocephalians improved on this system by developing heels on the lingual sides of the incisor teeth that met against one another to form a crushing surface when the jaws were shut.

Suggested intraspecific combat styles in dinocephalians. 1/top left: Face biting (Anteosauria), 2/top centre: head-butting (Tapinocephalidae e.g. Moschops), 3/ left: flank butting (Styracocephalus) 4/bottom left: locking and pushing (Estemmenosuchus) 5. bottom centre: stabbing (Struthiocephalus)

Most dinocephalians also developed a thickened (pachyostotic) and ornamented skull roof and braincase of varying and diverse form, sometimes with horn-like projections.[1] It has been widely suggested that tapinocephalids engaged in head-butting.[1] Other dinocephalians may have engaged in biting or head interlocking combat against rival individuals.[13]

The coronoid bones and the corresponding coronoid process on the lower jaw were lost in dinocephalians.[11]11,38

Limbs

Dinocephalian limb bones are generally optimised for muscle strength. Dinocephalians are likely to have had a sprawling posture,[14] or a posture intermediate between sprawling and upright.[9]

Evolutionary history

Dinocephalians first appeared during the early Roadian as evidence by remains found in Russia, but their geographic origin and early evolution like that of other therapsids in general is not clear.[15][16]

 
Anteosauria
 

Anteosauridae

 
 
Tapinocephalia
 
 

Estemmenosuchidae

 
 
 
 
 

Styracocephalidae

 
 
 
 

Titanosuchidae

 
 

Tapinocephalidae

 
 
 
 
 
Phylogeny of Dinocephalia following Fraser-King et al. 2019[17]

During the Wordian and early Capitanian, advanced dinocephalians radiated into a large number of herbivorous forms, representing a diverse megafauna. This is well known from the Tapinocephalus Assemblage Zone of the Southern African Karoo.

At the height of their diversity (middle or late Capitanian age) all the dinocephalians suddenly died out, during the Capitanian mass extinction event. The reason for their extinction is not clear; although disease, sudden climatic change, or other factors of environmental stress may have brought about their end. They were replaced by much smaller therapsids; herbivorous dicynodonts and carnivorous biarmosuchians, gorgonopsians and therocephalians.

Taxonomy

Estemmenosuchus, an estemmenosuchid
Anteosaurus, an anteosaur
Ulemosaurus, a tapinocephalian

Remains of dinocephalians were first described in the 19th century from Russia and South Africa, including Rhopalodon by Gotthelf Fischer von Waldheim in 1841, Deuterosaurus by Karl Eichwald in 1846, Tapinocephalus in 1876 and Titanosuchus in 1879 by Richard Owen, and Delphinognathus by Harry Seeley in 1892 (Delphinognathus is today considered an indeterminate juvenile tapinocephalid[18]). In 1894, Harry Seeley named Deuterosauria to encompass Rhopalodon and Deuterosaurus placing Deuterosauria as a suborder of Anomodontia. That same year, Seeley coined Dinocephalia to include Delphinognathus and Tapinocephalus, also as a suborder of Anomodontia. In 1903, Robert Broom included Rhopalodon and Deuteosaurus within the Therocephalia. By the 1910s Rhopalodon and Deuterosaurus were included within Dinocephalia, alongside Titanosuchus. During the mid 20th century, South African dinocephalians were subject to extensive study by Lieuwe Dirk Boonstra.[11]5-6

Up until the late 20th century, Dinocephalians were still generally considered to be members of Anomodontia (the group which contains dicynodonts and their close relatives), but this view was questioned during the 1990s,[19] and today is no longer widely accepted. The dominant paradigm of therapsid relationships as of the mid 2020s placed Dinocephalia as the second earliest diverging major group of therapsids, with Biarmosuchia being the most basal group, with Anomodontia being more closely related to Theriodontia (which includes Gorgonopsia, Therocephalia and Cynodontia, the last of which includes living mammals). A 2026 study instead placed Dinocephalia in a clade with Biarmosuchia, Raranimus and Biseridens at the base of Therapsida.[20]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 Benoit, Julien; Manger, Paul R.; Norton, Luke; Fernandez, Vincent; Rubidge, Bruce S. (2017-08-10). "Synchrotron scanning reveals the palaeoneurology of the head-butting Moschops capensis (Therapsida, Dinocephalia)" (in en). PeerJ 5. doi:10.7717/peerj.3496. ISSN 2167-8359. PMID 28828230. 
  2. ↑ Day, Michael O.; Guven, Saniye; Abdala, Fernando; Jirah, Sifelani; Rubidge, Bruce; Almond, John (2015). "Youngest dinocephalian fossils extend the Tapinocephalus Zone, Karoo Basin, South Africa". South African Journal of Science 111 (3/4): 1–5. doi:10.17159/sajs.2015/20140309. Bibcode: 2015SAJSc.111....1D. 
  3. ↑ "Driveria". https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=38994. 
  4. ↑ Nicolas, Merrill; Rubidge, Bruce S. (2010). "Changes in Permo-Triassic terrestrial tetrapod ecological representation in the Beaufort Group (Karoo Supergroup) of South Africa". Lethaia 43 (1): 45–59. doi:10.1111/j.1502-3931.2009.00171.x. Bibcode: 2010Letha..43...45N. 
  5. ↑ Kammerer, Christian F. (13 December 2010). "Systematics of the Anteosauria (Therapsida: Dinocephalia)". Journal of Systematic Palaeontology 9 (2): 261–304. doi:10.1080/14772019.2010.492645. 
  6. ↑ Angielczyk, K.D. (2009). "Dimetrodon is not a dinosaur: Using tree thinking to understand the ancient relatives of mammals and their evolution". Evolution: Education and Outreach 2 (2): 257–271. doi:10.1007/s12052-009-0117-4. 
  7. ↑ Simon, Rachel V.; Sidor, Christian A.; Angielczyk, Kenneth D.; Smith, Roger M.H. (2010). "First record of a Tempinocephalid (Therapsida: Dinocephalia) from the Ruhuhu Formation (Songea Group) of Southern Tanzania". Journal of Vertebrate Paleontology 30 (4): 1289–1293. doi:10.1080/02724634.2010.483549. Bibcode: 2010JVPal..30.1289S. 
  8. ↑ Mohd Shafi Bhat, Christen D. Shelton, Anusuya Chinsamy (2021). "Bone histology of dinocephalians (Therapsida, Dinocephalia): palaeobiological and palaeoecological inferences". Papers in Palaeontology 8 (1). doi:10.1002/spp2.1411. 
  9. ↑ 9.0 9.1 Romano, Marco; Rubidge, Bruce (2021-04-03). "First 3D reconstruction and volumetric body mass estimate of the tapinocephalid dinocephalian Tapinocaninus pamelae (Synapsida: Therapsida)" (in en). Historical Biology 33 (4): 498–505. doi:10.1080/08912963.2019.1640219. ISSN 0891-2963. Bibcode: 2021HBio...33..498R. https://www.tandfonline.com/doi/full/10.1080/08912963.2019.1640219. 
  10. ↑ Benoit, Julien; Midzuk, A. J. (2024-08-09). "Estimating the endocranial volume and body mass of Anteosaurus, Jonkeria, and Moschops (Dinocephalia, Therapsida) using 3D sculpting" (in English). Palaeontologia Electronica 27 (2): 1–11. doi:10.26879/1377. ISSN 1094-8074. https://palaeo-electronica.org/content/2024/5296-brain-size-in-dinocephalia. 
  11. ↑ 11.0 11.1 11.2 11.3 11.4 KING, G.M. 1988. Anomodontia. In: Wellnhofer, P. (ed.), Encyclopedia of Paleoherpetology. 174 pp. Stuttgart, Gustav Fischer.
  12. ↑ Lafferty, Tristen; Norton, Luke A.; Duhamel, Aliénor; Benoit, Julien (2025-09-08). "Description of the skull, braincase, and dentition of Moschognathus whaitsi (Dinocephalia, Tapinocephalia), and its palaeobiological and behavioral implications" (in en). The Anatomical Record. doi:10.1002/ar.70038. ISSN 1932-8486. PMID 40922509. https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.70038. 
  13. ↑ Bolton, Andrew D.; Mangera, Taahirah; Benoit, Julien (2025-08-12). "150 years of synapsid paleoneurology: the origins of the mammalian brain, behavior, sense organs and physiology" (in en). Journal of Paleontology: 1–29. doi:10.1017/jpa.2025.10121. ISSN 0022-3360. https://www.cambridge.org/core/product/identifier/S0022336025101212/type/journal_article. 
  14. ↑ Brocklehurst, Robert J.; Mercado, Magdalen; Angielczyk, Kenneth D.; Pierce, Stephanie E. (2025-06-24). Quental, Tiago Bosisio. ed. "Adaptive landscapes unveil the complex evolutionary path from sprawling to upright forelimb function and posture in mammals" (in en). PLOS Biology 23 (6). doi:10.1371/journal.pbio.3003188. ISSN 1545-7885. PMID 40554496. 
  15. ↑ Golubev, V. K. (December 2015). "Dinocephalian stage in the history of the Permian tetrapod fauna of Eastern Europe" (in en). Paleontological Journal 49 (12): 1346–1352. doi:10.1134/S0031030115120059. ISSN 0031-0301. Bibcode: 2015PalJ...49.1346G. https://link.springer.com/10.1134/S0031030115120059. 
  16. ↑ Duhamel, Alienor; Wynd, Brenen; Wright, April Marie; Moopen, Atashni; Benoit, Julien; Rubidge, Bruce (2026-03-11). "Rethinking therapsid phylogeny through Bayesian and cladistic approaches" (in en). Scientific Reports 16 (1). doi:10.1038/s41598-026-38195-2. ISSN 2045-2322. PMID 41813723. Bibcode: 2026NatSR..1613171D. 
  17. ↑ Fraser-King, Simon W.; Benoit, Julien; Day, Michael O.; Rubidge, Bruce S. (2019). "Cranial morphology and phylogenetic relationship of the enigmatic dinocephalian Styracocephalus platyrhynchus from the Karoo Supergroup, South Africa". Palaeontologia Africana 54: 14–29. http://wiredspace.wits.ac.za/handle/10539/28128. 
  18. ↑ Olroyd, Savannah L.; Sidor, Christian A. (2022-06-30). "Nomenclature, comparative anatomy, and evolution of the reflected lamina of the angular in non-mammalian synapsids" (in en). Journal of Vertebrate Paleontology 42 (1). doi:10.1080/02724634.2022.2101923. ISSN 0272-4634. Bibcode: 2022JVPal..42E1923O. https://www.tandfonline.com/doi/full/10.1080/02724634.2022.2101923. 
  19. ↑ Grine, F. E. (1997-04-16). "Dinocephalians are not anomodonts" (in en). Journal of Vertebrate Paleontology 17 (1): 177–183. doi:10.1080/02724634.1997.10010962. ISSN 0272-4634. http://www.tandfonline.com/doi/abs/10.1080/02724634.1997.10010962. 
  20. ↑ Duhamel, Alienor; Wynd, Brenen; Wright, April Marie; Moopen, Atashni; Benoit, Julien; Rubidge, Bruce (2026-03-11). "Rethinking therapsid phylogeny through Bayesian and cladistic approaches" (in en). Scientific Reports 16 (1). doi:10.1038/s41598-026-38195-2. ISSN 2045-2322. PMID 41813723. PMC 13103076. https://www.nature.com/articles/s41598-026-38195-2. 

Further reading

  • Carroll, R.L. (1988). Vertebrate Paleontology and Evolution. W.H. Freeman. 

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