Clevosaurus

Clevosaurus Temporal range: Late Triassic - Early Jurassic Carnian–Sinemurian PreꞒ Ꞓ O S D C P T J K Pg N
Skulls of Clevosaurus hudsoni (left) and C. cambrica (right)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Rhynchocephalia
Suborder:	Sphenodontia
Infraorder:	Eusphenodontia
Family:	† Clevosauridae
Genus:	† Clevosaurus Swinton, 1939
Species
See text
Synonyms
DianosaurusYoung, 1982

Clevosaurus (meaning "Gloucester lizard") is an extinct genus of rhynchocephalian reptile from the Late Triassic and the Early Jurassic periods. Species of Clevosaurus were widespread across Pangaea, and have been found on all continents except Australia and Antarctica. ^[1] Five species of Clevosaurus have been found in ancient fissure fill deposits in south-west England and Wales, alongside other sphenodontians, early mammals and dinosaurs. In regards to its Pangaean distribution, C. hadroprodon is the oldest record of a sphenodontian from Gondwana, ^[2] though its affinity to Clevosaurus has been questioned. ^[3]

Reconstructions of the skulls of C. hudsoni (A) and C. cambrica (B), reconstructed areas in orange.

History of discovery

The first species of Clevosaurus to be described was C. hudsoni, which was described by William Elgin Swinton in 1939 from a fissure fill deposit in Cromhall Quarry (Magnesian Conglomerate Formation) in the county of Gloucestershire, England, with the name of the county lending its name to the genus. ^[4]

Another notable specimen was discovered in 1953 in Cromhall Quarry alongside the holotype of Cryptovaranoides microlanius . ^[5]

Description

Skull of Clevosaurus brasiliensis

Species of Clevosaurus varied in body size, with Clevosaurus sectumsemper having an estimated total length of 12 centimetres (4.7 in), while C. hudsoni had a total length of around 25 centimetres (9.8 in). The skull length could range from as little as 1.4 centimetres (0.55 in) in C. sectumsemper and up to 4 centimetres (1.6 in) in C. hudsoni. ^[6] The reptilian encephalisation quotient (REQ) of C. brasiliensis is much lower than that of the modern tuatara, whose REQ is 0.84–1.16. ^[7] The teeth of European Clevosaurus tended to be mesio-distally elongated, blade-like, and occluded precisely with the opposite pair of teeth, leaving conspicuous diagonal wear facets and acting as a self-sharpening cutting surface. ^[8] However, the teeth of C. brasiliensis have a very different morphology with no diagonal wear facets, the teeth of the dentary are all conical excluding the posterior-most tooth which can be up to three-times bigger than any of the other teeth, they also have a unique form of implantation, where the base of the teeth sit deeply within the jaw bones, which is not known of in any other rhynchocephalian. ^[3]

Paleobiology

Life restoration of Clevosaurus hadroprodon

Species of Clevosaurus were likely insectivorous. Biomechanical modelling suggests that they had high enough tooth pressures and strong enough bite force to crush chitin, indicating that they had the ability to feed on thick-shelled beetles as well as possibly small vertebrates. ^[8]

Taxonomy

At least 9 species of Clevosaurus are considered valid:

• †Clevosaurus bairdi Sues et al. 1994 McCoy Brook Formation, Canada, Early Jurassic (Hettangian)
• †Clevosaurus brasiliensis Bonaparte and Sues 2006 ^[9] Caturrita Formation, Brazil, Late Triassic (Norian)
• †Clevosaurus cambrica Keeble et al. 2018 ^[6] Pant-y-ffynnon Quarry fissure fill, Wales, Late Triassic (Rhaetian)
• †Clevosaurus convallis Saila 2005 ^[10] St. Bride's Island fissure fill, Wales, Hettangian
• †Clevosaurus hadroprodon Hsiou et al. 2019 ^[11] Santa Maria Formation, Brazil, Late Triassic (Carnian)
• †Clevosaurus hudsoni Swinton 1939 Cromhall Quarry fissure fill, England, Rhaetian
• †Clevosaurus minor Fraser 1988 Cromhall Quarry fissure fill, England, Rhaetian
• †Clevosaurus sectumsemper Klein et al. 2015 ^[12] Woodleaze Quarry fissure fill, England, Rhaetian
• †Clevosaurus nicholasi Bhat et al. 2023 ^[13] Tiki Formation, India, late Carnian-middle Norian

The three species known from the Sinemurian aged Lufeng Formation of China (C. mcgilli, C.wangi and C. petilus) are now considered indeterminate within the genus. ^[14] Indeterminate remains are also known from the Stormberg Group (either Elliot or Clarens Formation) of South Africa, dating to the Hettangian. ^[1] Indeterminate clevosaur remains, possibly representing Clevosaurus, are also known from the Norian aged Fleming Fjord Group of Jameson Land, east Greenland. ^[15]

Below is a cladogram of the relationships within Clevosauridae based on the phylogenetic analysis of Hsiou et al. (2015): ^[16]

Clevosauridae	Polysphenodon mulleri Brachyrhinodon taylori Clevosaurus sp. (South Africa) Clevosaurus convallis Clevosaurus hudsoni Clevosaurus petilus Clevosaurus bairdi Clevosaurus mcgilli Clevosaurus wangi Clevosaurus brasiliensis Clevosaurus cambrica

"Clevosaurus" latidens was recovered outside of Clevosauridae, as the sister taxon of Opisthodontia. ^[16] It was subsequently assigned to a new genus, Fraserosphenodon , in 2018. ^[17]

Clevosaurus is considered to be a member of the group Eusphenodontia by the groups definition, due to it possessing characters not shared with more primitive sphenodontians. By definition, it is excluded from Neosphenodontia. ^[17]

Position of Clevosaurus within Rhynchocephalia, after DeMar et al. 2022. ^[18]

Younginia capensis Prolacerta broomi Lepidosauria Pan-Squamata Sophineta cracoviensis Pristidactylus Eichstaettisaurus schroederi Megachirella wachtleri Marmoretta oxoniensis Rhynchocephalia Gephyrosaurus bridensis Sphenodontia Diphydontosaurus avonis Acrosphenodontia Planocephalosaurus robinsonae Rebbanasaurus jaini Godavarisaurus lateefi Theretairus antiquus Eusphenodontia Polysphenodon mulleri Opisthiamimus gregori Clevosaurus Clevosaurus convallis Clevosaurus brasiliensis Clevosaurus hadroprodon Clevosaurus bairdi Clevosaurus hudsoni Clevosaurus cambrica Neosphenodontia Brachyrhinodon taylori Colobops noviportensis Sphenodontidae Sphenodon punctatus Cynosphenodon huizachalensis Sphenovipera jimmysjoyi Kawasphenodon expectatus Kawasphenodon peligrensis Pelecymala robustus Eilenodontinae Fraserosphenodon latidens Opisthias rarus Eilenodon robustus Sphenotitan leyesi Toxolophosaurus cloudi Priosphenodon avelasi Leptorhynchia Homoeosaurus maximiliani Kallimodon pulchellus Sigmala sigmala Vadasaurus herzogi Pleurosauridae Palaeopleurosaurus posidonae Pleurosaurus goldfussi Pleurosaurus ginsburgi Kallimodon cerinensis Sapheosauridae Sapheosaurus thiollierei Ankylosphenodon pachyostosus Oenosaurus muehlheimensis

References

1. Sues, H. D.; Reisz, R. (1995). "First record of the early mesozoic sphenodontian clevosaurus (lepidosauria: rhynchocephalia) from the southern hemisphere". Journal of Paleontology. 69 (1): 123–126. Bibcode:1995JPal...69..123S. doi:10.1017/s0022336000026974. S2CID   131414921.
2. "A new sphenodontian from Brazil is the oldest record of the group in Gondwana". phys.org. Retrieved 2019-08-15.
3. Chambi-Trowell, Sofia A. V.; Martinelli, Agustín G.; Whiteside, David I.; Vivar, Paulo R. Romo de; Soares, Marina Bento; Schultz, Cesar L.; Gill, Pamela G.; Benton, Michael J.; Rayfield, Emily J. (2021-06-03). "The diversity of Triassic South American sphenodontians: a new basal form, clevosaurs, and a revision of rhynchocephalian phylogeny". Journal of Systematic Palaeontology. 19 (11): 787–820. Bibcode:2021JSPal..19..787C. doi: 10.1080/14772019.2021.1976292 . hdl: 1983/af14affc-a26e-426b-83ca-e1833e355882 . ISSN   1477-2019. S2CID   240487298.
4. W. E. Swinton. (1939). A new Triassic rhynchocephalian from Gloucestershire. Annals and Magazine of Natural History: Zoology, Botany, and Geology4:591-594
5. Whiteside, D. I.; Chambi-Trowell, S. A. V.; Benton, Michael James (2022). "A Triassic crown squamate". Science Advances . 8 (48): eabq8274. Bibcode:2022SciA....8.8274W. doi:10.1126/sciadv.abq8274. hdl: 1983/a3c7a019-cfe6-4eb3-9ac0-d50c61c5319e . ISSN   2375-2548. PMC   10936055 . PMID   36459546.
6. Keeble, Emily; Whiteside, David I.; Benton, Michael J. (April 2018). "The terrestrial fauna of the Late Triassic Pant-y-ffynnon Quarry fissures, South Wales, UK and a new species of Clevosaurus (Lepidosauria: Rhynchocephalia)" . Proceedings of the Geologists' Association . 129 (2): 99–119. Bibcode:2018PrGA..129...99K. doi:10.1016/j.pgeola.2017.11.001. hdl: 1983/5afdc677-3ea0-4519-813d-6052ef8370ec .
7. Roese‐Miron, Lívia; Jones, Marc Emyr Huw; Ferreira, José Darival; Hsiou, Annie Schmaltz (23 March 2023). "Virtual endocasts of Clevosaurus brasiliensis and the tuatara: Rhynchocephalian neuroanatomy and the oldest endocranial record for Lepidosauria" . The Anatomical Record . 307 (4): 1366–1389. doi:10.1002/ar.25212. ISSN   1932-8486 . Retrieved 16 June 2025– via Wiley Online Library.
8. Chambi-Trowell, Sofia A. V.; Whiteside, David I.; Benton, Michael J.; Rayfield, Emily J. (16 June 2020). Lautenschlager, Stephan (ed.). "Biomechanical properties of the jaws of two species of Clevosaurus and a reanalysis of rhynchocephalian dentary morphospace" . Palaeontology . 63 (6): 919–939. Bibcode:2020Palgy..63..919C. doi:10.1111/pala.12493. ISSN   0031-0239. S2CID   220902843.
9. Bonaparte, J. F.; Sues, H. D. (2006). "A new species of clevosaurus (lepidosauria: rhynchocephalia) from the upper Triassic of Rio Grande do Sul, Brazil". Palaeontology. 49 (1): 917–923. Bibcode:2006Palgy..49..917B. doi: 10.1111/j.1475-4983.2006.00568.x . S2CID   26483165.
10. Säilä, Laura K. (2005). "A new species of the sphenodontian reptile Clevosaurus from the Lower Jurassic of South Wales". Palaeontology. 48 (4): 817–831. Bibcode:2005Palgy..48..817S. doi: 10.1111/j.1475-4983.2005.00486.x .
11. Hsiou, Annie S.; Nydam, Randall L.; Simões, Tiago R.; Pretto, Flávio A.; Onary, Silvio; Martinelli, Agustín G.; Liparini, Alexandre; Martínez, Paulo R. Romo de Vivar; Soares, Marina B.; Schultz, Cesar L.; Caldwell, Michael W. (2019-08-14). "A New Clevosaurid from the Triassic (Carnian) of Brazil and the Rise of Sphenodontians in Gondwana". Scientific Reports . 9 (1): 11821. Bibcode:2019NatSR...911821H. doi:10.1038/s41598-019-48297-9. ISSN   2045-2322. PMC   6694142 . PMID   31413294.
12. Klein, Catherine G.; Whiteside, David I.; de Lucas, Victor Selles; Viegas, Pedro A.; Benton, Michael J. (2015). "A distinctive Late Triassic microvertebrate fissure fauna and a new species of Clevosaurus (Lepidosauria: Rhynchocephalia) from Woodleaze Quarry, Gloucestershire, UK". Proceedings of the Geologists' Association. 126 (3): 402–416. Bibcode:2015PrGA..126..402K. doi:10.1016/j.pgeola.2015.05.003.
13. Bhat, Mohd Shafi; Datta, Debajit; Ray, Sanghamitra; Datta, P. M. (2023-01-02). "A new clevosaurid (Lepidosauria: Rhynchocephalia) from the Upper Triassic of IndiaCitation for this article: Bhat, M. S., Datta, D., Ray, S., & Datta, P. M. (2023) A new clevosaurid (Lepidosauria: Rhynchocephalia) from the Upper Triassic of India. Journal of Vertebrate Paleontology" . Journal of Vertebrate Paleontology. 43 (1). Bibcode:2023JVPal..43E2833B. doi:10.1080/02724634.2023.2232833. ISSN   0272-4634. S2CID   260525273.
14. Jones MEH. 2006 The Early Jurassic clevosaurs from China (Diapsida: Lepidosauria). New Mex. Museum Nat. Hist. Sci. Bull. 37, 548–562.
15. Jésus, Valerian J. P.; Mateus, Octávio; Milàn, Jesper; Clemmensen, Lars B. (2025-04-15). "Late Triassic small and medium-sized vertebrates from the Fleming Fjord Group of the Jameson Land Basin, central East Greenland". Palaeontologia Electronica. 28 (1): 1–21. doi:10.26879/1423. ISSN   1094-8074.
16. Annie Schmaltz Hsiou; Marco Aurélio Gallo De França; Jorge Ferigolo (2015). "New Data on the Clevosaurus (Sphenodontia: Clevosauridae) from the Upper Triassic of Southern Brazil". PLOS ONE. 10 (9): e0137523. Bibcode:2015PLoSO..1037523H. doi: 10.1371/journal.pone.0137523 . PMC   4565693 . PMID   26355294.
17. Jorge A. Herrera-Flores; Thomas L. Stubbs; Armin Elsler; Michael J. Benton (2018). "Taxonomic reassessment of Clevosaurus latidens Fraser, 1993 (Lepidosauria, Rhynchocephalia) and rhynchocephalian phylogeny based on parsimony and Bayesian inference". Journal of Paleontology. 92 (4): 734–742. Bibcode:2018JPal...92..734H. doi: 10.1017/jpa.2017.136 . hdl: 1983/59126b60-16d8-46d2-b657-954693a39d4e .
18. DeMar, David G.; Jones, Marc E. H.; Carrano, Matthew T. (2022-12-31). "A nearly complete skeleton of a new eusphenodontian from the Upper Jurassic Morrison Formation, Wyoming, USA, provides insight into the evolution and diversity of Rhynchocephalia (Reptilia: Lepidosauria)". Journal of Systematic Palaeontology. 20 (1): 1–64. doi:10.1080/14772019.2022.2093139. hdl: 2440/136608 . ISSN   1477-2019. S2CID   252325953.

Additional reading

• Paleofile
• Gill PG, Säilä LK, Corfe IJ, Challands TJ, Williams M, Clemens WA (2006). The fauna and palaeoenvironment of St. Brides Island: Evidence from the lower Jurassic fissure fills of South Wales. In Barrett PM, Evans SE (eds.). Ninth international symposium on Mesozoic terrestrial ecosystems and biota. pp 48−51. London: Natural History Museum.
• Jones MEH (2006) The Early Jurassic clevosaurs from China (Diapsida: Lepidosauria). Natl Mus Nat Hist Sci Bull, 37:548–562.
• Jones MEH (2009). Dentary tooth shape in Sphenodon and its fossil relatives (Diapsida: Lepidosauria: Rhynchocephalia). In Koppe T, Meyer G, Alt KW, (eds). Interdisciplinary Dental Morphology, Frontiers of Oral Biology (vol 13). Greifswald, Germany; Karger. 9–15.

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