Youngina

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Youngina (named after John Young (1823–1900)) is an extinct genus of small, lizard-like stem-group reptile from the Late Permian Beaufort Group (Cistecephalus–Daptocephalus assemblage zones) of the Karoo Supergroup of South Africa. Youngina has been the subject of considerable scientific attention due to its basal position within Neodiapsida (having diverged before the last common ancestor of all living reptiles)[1][2][3] and its well-preserved skulls, with Youngina seen as providing insight into the plesiomorphic (ancestral) morphology of the last common ancestor of living reptiles.[4]

History

The holotype, a skull and associated vertebrae, was discovered by Robert Broom near Nieu-Bethesda, Cape Colony (now South Africa)[5] and he published his brief description of Youngina capensis in 1914.[6] Another well-preserved skull was described by Olsen (1936).[7]

SAM-PK-K7710, an aggregation of several small, articulated reptiles embedded in siltstone, was assigned to Youngina by Smith & Evans (1995) and regarded as a representative of this species for many years.[8] It was moved to its own species, Scyllacerta creanae, by Jenkins et al. (2026).[3]

Description

File:Youngina skull lateral.png
Reconstructed skull
File:Youngina Scale.svg
Size compared to a human hand

Youngina was a relatively small reptile, with a skull length of 5 centimetres (2.0 in) and a total body length of 30 centimetres (12 in).[4] The braincase anatomy of the holotype skull was redescribed in 2010 based on CT scans.[9] Youngina shows a mosaic of features found in more primitive diapsids and more derived taxa such as archosauromorphs and lepidosauromorphs suggesting a non-orthogenetic evolution of these characters. Though the palatobasal articulation is open,[9] it was probably immobile, similar to the skull of the tuatara,[10] contrary to some earlier claims made about the metakinetic mobility of basicranial joints in Youngina and other early diapsid reptiles.[11] In 2023, Hunt et al. described the palate and mandible of another skull referred to Youngina, BP/1/2871. These authors used this new data to determine Youngina is likely more basal than previously thought in relation to crown-group reptiles.[4]

Taxonomy and phylogeny

Youngina is known from several specimens. Many of these were attributed to as separate genera and species (such as Youngoides and Youngopsis), but it was later realized that they were not distinct from Y. capensis.[5][12] The "Youngoides romeri" specimen was first attributed to Youngina,[7] but later given its eponymous and separate designation in a later paper.[13] Acanthotoposaurus[14] is also a junior synonym of Youngina.[15]

Youngina is currently placed in the family Younginidae, which comprises the earliest diverging members of Neodiapsida that lie outside of Sauria, the clade that contains all living reptiles (and birds).[4] Youngina was historically placed within the group "Eosuchia" by authors such as Alfred Sherwood Romer alongside various other Permian-Triassic reptile groups like the millerettids, thalattosaurs, rhynchocephalians and rhynchosaurs, which are now thought to form a paraphyletic group of unrelated reptiles.[16][17] Youngina was later placed with the group Younginiformes alongside other Permian-Triassic lizard-like diapsid reptiles from East Africa and Madagascar, including Acerosodontosaurus, Kenyasaurus, Hovasaurus, Thadeosaurus, and Tangasaurus. However, the monophyly of this group has been strongly questioned, and the group as a whole has often been recovered as paraphyletic.[18] Below is a cladogram from the analysis of Reisz et al. (2011) showing the phylogenetic position of Youngina among early diapsids and a paraphyletic "Younginiformes".[19]Script error: No such module "Clade".Implied weighting analysis after Jenkins et al. 2026:[3]Script error: No such module "Clade".

References

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  1. ^ Page Module:Citation/CS1/styles.css has no content.Pritchard, Adam C.; Sues, Hans-Dieter; Scott, Diane; Reisz, Robert R. (2021-05-20). "Osteology, relationships and functional morphology of Weigeltisaurus jaekeli (Diapsida, Weigeltisauridae) based on a complete skeleton from the Upper Permian Kupferschiefer of Germany". PeerJ. 9 e11413. doi:10.7717/peerj.11413. ISSN 2167-8359. PMC 8141288. PMID 34055483.
  2. ^ Page Module:Citation/CS1/styles.css has no content.Buffa, Valentin; Jenkins, Xavier A.; Benoit, Julien (2025-12-31). "Galesphyrus capensis from the Permian of South Africa and the origin of Neodiapsida". Journal of Systematic Palaeontology. 23 (1) 2563582. Bibcode:2025JSPal..2363582B. doi:10.1080/14772019.2025.2563582. ISSN 1477-2019.
  3. ^ a b c Page Module:Citation/CS1/styles.css has no content.Jenkins, Xavier A.; Buffa, Valentin; Marchant, Cy J.; Ford, David P.; Browning, Claire; Fernandez, Vincent; Dollman, Kathleen; Botha, Jennifer; Choiniere, Jonah N.; Benson, Roger B. J.; Peecook, Brandon R. (2026). "The origin of the tympanic fossa in reptiles revealed by a late Permian neodiapsid". Palaeontology. 69 (1) e70041. doi:10.1111/pala.70041. ISSN 1475-4983.
  4. ^ a b c d Page Module:Citation/CS1/styles.css has no content.Hunt, Annabel K.; Ford, David P.; Fernandez, Vincent; Choiniere, Jonah N.; Benson, Roger B. J. (September 2023). "A description of the palate and mandible of Youngina capensis (Sauropsida, Diapsida) based on synchrotron tomography, and the phylogenetic implications". Papers in Palaeontology. 9 (5) e1521. Bibcode:2023PPal....9E1521H. doi:10.1002/spp2.1521. ISSN 2056-2799.
  5. ^ a b Page Module:Citation/CS1/styles.css has no content.Gow, C. E. (1975). "The morphology and relationships of Youngina capensis Broom and Prolacerta broomi Parrington". Palaeontologia Africana. 18: 89–131. hdl:10539/16290.
  6. ^ Page Module:Citation/CS1/styles.css has no content.Broom, R. (1914). "A new thecodont reptile". Proceedings of the Zoological Society of London. B. 84 (4): 1072–1077. doi:10.1111/j.1469-7998.1914.tb07729.x.
  7. ^ a b Page Module:Citation/CS1/styles.css has no content.Olson, E. C. (1936). "Notes on the skull of Youngina capensis Broom". Journal of Geology. 44 (4): 523–533. Bibcode:1936JG.....44..523O. doi:10.1086/624447. JSTOR 30068180. S2CID 140142731.
  8. ^ Page Module:Citation/CS1/styles.css has no content.Smith, Roger M. H.; Evans, Susan E. (1995). "An aggregation of juvenile Youngina from the Beaufort Group, Karoo Basin, South Africa". Palaeontologia Africana. 32: 45–49.
  9. ^ a b Page Module:Citation/CS1/styles.css has no content.Gardner, Nicholas M.; Holliday, Casey M.; O'Keefe, F. Robin (2010). "The braincase of Youngina capensis (Reptilia, Diapsida): new insights from high-resolution CT scanning of the holotype" (PDF). Palaeontologia Electronica. 13 (3): 19A.
  10. ^ Page Module:Citation/CS1/styles.css has no content.Johnston, P. (2010). "The constrictor dorsalis musculature and basipterygoid articulation in Sphenodon". Journal of Morphology. 271 (3): 280–292. Bibcode:2010JMorp.271..280J. doi:10.1002/jmor.10797. PMID 19806656. S2CID 32965233.
  11. ^ Page Module:Citation/CS1/styles.css has no content.Evans, S. E. (1980). "The skull of a new eosuchian reptile from the Lower Jurassic of South Wales". Zoological Journal of the Linnean Society. 70 (3): 203–264. doi:10.1111/j.1096-3642.1980.tb00852.x.
  12. ^ Page Module:Citation/CS1/styles.css has no content.Evans, S. E. (1987). "The braincase of Youngina capensis (Reptilia: Diapsida; Permian)". Neues Jahrb. Geol. Paläontol. Monats. 1987: 193–203.
  13. ^ Page Module:Citation/CS1/styles.css has no content.Olson, E. C.; Broom, R. (1937). "New genera and species of tetrapods form the Karroo beds of South Africa". Journal of Paleontology. 11 (7): 613–619. JSTOR 1298390.
  14. ^ Page Module:Citation/CS1/styles.css has no content.Evans, S. E.; Van der Heever, J. A. (1987). "A new reptile (Reptilia: Diapsida) from the Upper Permian Daptocephalus zone of South Africa". South African Journal of Science. 83 (11): 724–730.[dead link]
  15. ^ Page Module:Citation/CS1/styles.css has no content.Reisz, R. R.; Modesto, S. P.; Scott, D. (2000). "Acanthotoposaurus bremneri and the origin of the Triassic archosauromorphreptile fauna of South Africa". South African Journal of Science. 96 (8): 443–445.
  16. ^ Page Module:Citation/CS1/styles.css has no content.Bastiaans, Dylan (December 2024). "Thalattosauria in time and space: a review of thalattosaur spatiotemporal occurrences, presumed evolutionary relationships and current ecological hypotheses". Swiss Journal of Palaeontology. 143 (1) 36. Bibcode:2024SwJP..143...36B. doi:10.1186/s13358-024-00333-6. ISSN 1664-2376. PMC 11427521. PMID 39345254.
  17. ^ Page Module:Citation/CS1/styles.css has no content.Jenkins, Xavier A.; Benson, Roger B. J.; Ford, David P.; Browning, Claire; Fernandez, Vincent; Griffiths, Elizabeth; Choiniere, Jonah; Peecook, Brandon R. (January 2025). "Cranial osteology and neuroanatomy of the late Permian reptile Milleropsis pricei and implications for early reptile evolution". Royal Society Open Science. 12 (1) 241298. Bibcode:2025RSOS...1241298J. doi:10.1098/rsos.241298. ISSN 2054-5703. PMC 11707879. PMID 39780968.
  18. ^ Page Module:Citation/CS1/styles.css has no content.Bickelmann; Müller; Reisz (2009). "The enigmatic diapsid Acerosodontosaurus piveteaui (Reptilia: Neodiapsida) from the Upper Permian of Madagascar and the paraphyly of "younginiform" reptiles". Canadian Journal of Earth Sciences. 46 (9): 651–661. Bibcode:2009CaJES..46..651S. doi:10.1139/E09-038.
  19. ^ Page Module:Citation/CS1/styles.css has no content.Reisz, Robert R.; Modesto, Sean P.; Scott, Diane M. (2011). "A new Early Permian reptile and its significance in early diapsid evolution". Proceedings of the Royal Society B. 278 (1725): 3731–3737. Bibcode:2011PBioS.278.3731R. doi:10.1098/rspb.2011.0439. PMC 3203498. PMID 21525061.

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