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Estemmenosuchus

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Estemmenosuchus
Temporal range: Guadalupian (Wordian), 267 Ma
E. uralensis skeleton
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Clade: Therapsida
Suborder: †Dinocephalia
Family: †Estemmenosuchidae
Genus: †Estemmenosuchus
Tchudinov, 1960
Species
  • †E. uralensis Tchudinov, 1960 (type)
  • †E. mirabilis Tchudinov, 1968
Synonyms
  • Anoplosuchus tenuirostris Tchudinov, 1968
  • Zopherosuchus luceus Tchudinov, 1963

Estemmenosuchus (meaning "crowned crocodile" in Greek) is an extinct genus of large, early herbivorous dinocephalian therapsid. It lived during the Middle Permian around 267 million years ago. The two species, E. uralensis and E. mirabilis, are characterised by distinctive horn-like structures, which were probably used for intra-specific display and/or combat. Both species of Estemmenosuchus are from the Perm (or Cis-Urals) region of Russia. Two other estemmenosuchids, Anoplosuchus and Zopherosuchus, are now considered females of the species E. uralensis.[1] There were many complete and incomplete skeletons found together.

Description

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Skull of E. mirabilis

Estemmenosuchus could reach a body length of more than 3 m (10 ft).[2] Its skull was long and massive, up to 65 cm (26 in) in length.[2] The temporal fenestrae are relatively large.[3] There are a distinct set of horn like-growths formed by the frontal, postfrontal and probably the postorbitals, as well as another large growth on the lower part of the jugal bone. There are 5 pairs of incisors, one pair of canines, and 20 pairs of postcanine teeth in the upper jaw, and four pairs of incisors, one pair of canines, and 20-24 pairs of postcanine teeth in the lower jaw. The canine teeth are relatively short and thick relative to other dinocephalians. The postcanine teeth are relatively small, with the crown being swollen and the apex of the postcanine teeth being narrow and serrated.[4]12 Like other dinocephalians, the incisor teeth are intermeshing.[5] Estemmenosuchus is the only known therapsid to possess palatal teeth (teeth on the roof of the mouth) on the vomer bone, with palatal teeth also present on the pterygoid and palatine bones like other therapsids.[6] Estemmenosuchus may also have had osteoderms (bony growths) embedded in its skin.[7]

Estemmenosuchus is well known for being one of the few non-mammalian therapsids (alongside the dicynodont Lystrosaurus) to have preserved skin impressions.[8] The skin appears to be scaleless, possibly preserving the remnants of melanin pigment, and covered in numerous small spherical tubercles around 0.3–0.45 millimetres (3⁄256–9⁄512 in) across, which may represent glands.[9][10]

Taxonomy

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Life restoration of E. uralensis

Estemmenosuchus is interpreted to have lived some 267 million years ago. Two species have been identified, from the Ocher Assemblage Zone Belebei Formation at the Ezhovo locality near Ochyor in the Perm region of the Russia in 1960. They were found with the biarmosuchians Eotitanosuchus olsoni and Biarmosuchus tener in channel flood deposits of the young Ural Mountains. They differ in size, shape of the skull, and shape of the horns.

Originally all specimens were included in Estemmenosuchus uralensis, but it was since realised that there were a number of different species. However, not all palaeontologists agree that these were different species. According to Ivakhnenko (1998) Anoplosuchus and Zopherosuchus are synonyms of Estemmenosuchus uralensis.[11]

SpeciesStatusAbundance[11]Remains[11]Skull lengthBody Length[11]NotesImages
Anoplosuchus tenuirostrisSynonym of Estemmenosuchus uralensisFairly uncommonIncomplete skeleton and skullIntermediate in sizeThere are no horns or thickening, except in the front nasal region.[11]
Estemmenosuchus mirabilisValid speciesFairly uncommonSkull, lower jaw and vertebraeUp to 42 cm long3 m longUnlike E. uralensis, which had only one horn on each side of its head, this species had 2 projecting bony knobs on each side of the cranium, one on the top pointing up looking like antlers and another pointing to the side similar to E. uralensis. Its snout is smaller and wider than its relative and looks vaguely like a modern moose. The palate teeth include six incisors, two canines and about twenty small incisor-like teeth at the rear. The lower palate contained six incisors, two canines and about thirty smaller back teeth.
Estemmenosuchus uralensisValid speciesCommonElements of skulls and postcraniaUp to 68 cm long4.5 m longThe species are characterised by horns which project upward and outward on the side of the head. The mouth contained large canines with small molar teeth.
Zopherosuchus luceusSynonym of Estemmenosuchus uralensisFairly uncommonPoorly preserved skeleton and incomplete skull1.5 m longSome of bones at the front of the skull are particularly thickened.[11]

Estemmenosuchus is currently classified as one of the most basal members of the largely herbivorous Tapinocephalia, one of the two main subdivisions of Dinocephalia. Below is a cladogram depicting the relationship of the Estemmenosuchus with other dinocephalians based on a phylogenetic study published in 2019.[12]

Dinocephalia

Paleobiology

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Estemmenosuchus has been inferred to be herbivorous.[13]

Thermoregulation

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A painting of an Estemmenosuchus wallowing in a lake

It has been suggested that the animal had a fairly constant internal temperature. Its large size and compact build gave a small surface-to-volume ratio and suggests it would not gain (or lose) temperature quickly. This phenomenon is called gigantothermy and was probably an important factor in temperature regulation in most therapsids.[14]

Function of horns

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Proposed combat pose between rival Estemmenosuchus individuals

Species of Estemmenosuchus may have engaged in fighting behaviour against rival individuals of the same species using their head ornamentation, as has been suggested for other dinocephalians. The complex head ornamentation of Estemmenosuchus in particular may have served for lock and pushing combat, functioning similar to antlers in living deer species, as its skull is less adapted for heavy blows than other dinocephalians. Like modern ungulates, their head ornamentation may have also served for display alongside combat.[15]

References

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  1. ↑ Ivakhnenko, M.F. (2000). "Estemmenosuchus and primitive theriodonts from the Late Permian". Paleontological Journal. 34 (2): 184–192.
  2. 1 2 Ivakhnenko, M. F. (2001). "Tetrapods from the East European Placket—Late Paleozoic Natural Territorial Complex". Proceedings of the Paleontological Institute of the Russian Academy of Sciences (in Russian). 283: 200.
  3. ↑ Rubidge, Bruce S.; Sidor, Christian A. (November 2001). "Evolutionary Patterns Among Permo-Triassic Therapsids". Annual Review of Ecology and Systematics. 32 (1): 449–480. Bibcode:2001AnRES..32..449R. doi:10.1146/annurev.ecolsys.32.081501.114113. ISSN 0066-4162.
  4. ↑ KING, G.M. 1988. Anomodontia. In: Wellnhofer, P. (ed.), Encyclopedia of Paleoherpetology. 174 pp. Stuttgart, Gustav Fischer.
  5. ↑ Rubidge, Bruce S.; Sidor, Christian A. (November 2001). "Evolutionary Patterns Among Permo-Triassic Therapsids". Annual Review of Ecology and Systematics. 32 (1): 449–480. Bibcode:2001AnRES..32..449R. doi:10.1146/annurev.ecolsys.32.081501.114113. ISSN 0066-4162.
  6. ↑ Matsumoto, Ryoko; Evans, Susan E. (January 2017). "The palatal dentition of tetrapods and its functional significance". Journal of Anatomy. 230 (1): 47–65. doi:10.1111/joa.12534. ISSN 0021-8782. PMC 5192890. PMID 27542892.
  7. ↑ Chudinov, P.K. (1983). Ranniye terapsidy [Early therapsids]. Trudy Paleontologicheskogo Instituta Akademii Nauk SSSR, 202, (In Russian) p. 186
  8. ↑ Mooney, Ethan D.; Maho, Tea; Philp, R. Paul; Bevitt, Joseph J.; Reisz, Robert R. (January 22, 2024). "Paleozoic cave system preserves oldest-known evidence of amniote skin". Current Biology. 34 (2): 417–426.e4. Bibcode:2024CBio...34..417M. doi:10.1016/j.cub.2023.12.008. ISSN 0960-9822. PMID 38215745.
  9. ↑ Chudinov, P. K. (1968). "Structure of the integuments of theromorphs". Doklady Akademii Nauk SSSR. 179 (1): 207–210.
  10. ↑ Dhouailly, Danielle; Godefroit, Pascal; Martin, Thomas; Nonchev, Stefan; Caraguel, Flavien; Oftedal, Olav (April 2019). "Getting to the root of scales, feather and hair: As deep as odontodes?". Experimental Dermatology. 28 (4): 503–508. doi:10.1111/exd.13391. ISSN 0906-6705.
  11. 1 2 3 4 5 6 "Therapsida: Dinocephalia: Estemmenosuchidae". Palaeos. Archived from the original on July 10, 2015. Retrieved October 23, 2015.
  12. ↑ 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.
  13. ↑ Kemp, T. S. (July 1, 2006). "The origin and early radiation of the therapsid mammal-like reptiles: a palaeobiological hypothesis". Journal of Evolutionary Biology. 19 (4): 1231–1247. doi:10.1111/j.1420-9101.2005.01076.x. ISSN 1010-061X.
  14. ↑ Ruben, J.A.; Jones, T.D. (2000). "Selective Factors Associated with the Origin of Fur and Feathers". Am. Zool. 40 (4): 585–596. doi:10.1093/icb/40.4.585.
  15. ↑ Bolton, Andrew D.; Mangera, Taahirah; Benoit, Julien (August 12, 2025). "150 years of synapsid paleoneurology: the origins of the mammalian brain, behavior, sense organs and physiology". Journal of Paleontology: 1–29. doi:10.1017/jpa.2025.10121. ISSN 0022-3360.

Further reading

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