Youngina

{{Automatic taxobox

| fossil_range = Late Permian, {{fossil range|259.9|254.17}}

| image = Youngina capensis.png

| image_caption = Speculative life restoration

| display_parents = 3

| taxon = Youngina

| authority = {{harvnb|Broom|1914}}

| type_species = {{extinct}}Youngina capensis

| type_species_authority = {{harvnb|Broom|1914}}

}}

Youngina (named after John Young (1823–1900)) is an extinct genus of diapsid reptile from the Late Permian Beaufort Group (Tropidostoma-Dicynodon zones) of the Karoo Red Beds of South Africa.{{cite journal |last1=Smith |first1=R. |last2=Evans |first2=S. |year=1996 |title=New Material of Youngina: Evidence of Juvenile Aggregation in Permian Diapsid Reptiles |journal=Palaeontology |volume=39 |issue=2 |pages=289–303 |url=https://www.palass.org/sites/default/files/media/publications/palaeontology/volume_39/vol39_part2_pp289-303.pdf |archive-url=https://web.archive.org/web/20190730162144/https://www.palass.org/sites/default/files/media/publications/palaeontology/volume_39/vol39_part2_pp289-303.pdf |archive-date=2019-07-30 |url-status=live }} This, and a few related forms, make up the family Younginidae, within the order Eosuchia (proposed by Broom in 1914). Eosuchia, having become a wastebasket taxon for many probably distantly-related primitive diapsid reptiles ranging from the Late Carboniferous to the Eocene, Romer proposed that it be replaced by Younginiformes (that included Younginidae and the Tangasauridae, ranging from the Permian to the Triassic).

Taxonomy

File:Youngina skull lateral.png

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.{{cite journal |last=Gow |first=C. E. |year=1975 |title=The morphology and relationships of Youngina capensis Broom and Prolacerta broomi Parrington |journal=Palaeontologia Africana |volume=18 |pages=89–131 |hdl=10539/16290}}{{cite journal |last=Evans |first=S. E. |year=1987 |title=The braincase of Youngina capensis (Reptilia: Diapsida; Permian) |journal=Neues Jahrb. Geol. Paläontol. |series=Monats. |volume=1987 |pages=193–203 }} The holotype specimen of Youngina, discovered by Broom himself, was described briefly in 1914.{{cite journal |last=Broom |first=R. |author-link=Robert Broom |year=1914 |title=A new thecodont reptile |journal=Proceedings of the Zoological Society of London |series=B |volume=84 |issue=4 |pages=1072–1077 |doi=10.1111/j.1469-7998.1914.tb07729.x |url=https://archive.org/details/cbarchive_100650_1914anewthecodontreptileprocee1833/page/n1}} The "Youngoides romeri" specimen was first attributed to Youngina,{{cite journal |last=Olson |first=E. C. |year=1936 |title=Notes on the skull of Youngina capensis Broom |journal=Journal of Geology |volume=44 |issue=4 |pages=523–533 |jstor=30068180 |doi=10.1086/624447|bibcode=1936JG.....44..523O |s2cid=140142731 }} but later given its eponymous and separate designation in a later paper.{{cite journal |last1=Olson |first1=E. C. |last2=Broom |first2=R. |year=1937 |title=New genera and species of tetrapods form the Karroo beds of South Africa |journal=Journal of Paleontology |volume=11 |issue=7 |pages=613–619 |jstor=1298390 }} Acanthotoposaurus{{cite journal |last1=Evans |first1=S. E. |last2=Van der Heever |first2=J. A. |year=1987 |title=A new reptile (Reptilia: Diapsida) from the Upper Permian Daptocephalus zone of South Africa |journal=South African Journal of Science |volume=83 |issue=11 |pages=724–730 |url=http://discovery.ucl.ac.uk/id/eprint/1497751 }} is also a junior synonym of Youngina.{{cite journal |last1=Reisz |first1=R. R. |last2=Modesto |first2=S. P. |last3=Scott |first3=D. |year=2000 |title=Acanthotoposaurus bremneri and the origin of the Triassic archosauromorphreptile fauna of South Africa |journal=South African Journal of Science |volume=96 |issue=8 |pages=443–445 |url=https://journals.co.za/content/sajsci/96/8/AJA00382353_8965 }}

Description

File:Youngina Scale.svg

Youngina was a relatively small reptile, with a skull length of {{Convert|5|cm|in}} and a total body length of {{Convert|30|cm|in}}.{{Cite journal |last=Hunt |first=Annabel K. |last2=Ford |first2=David P. |last3=Fernandez |first3=Vincent |last4=Choiniere |first4=Jonah N. |last5=Benson |first5=Roger B. J. |date=September 2023 |title=A description of the palate and mandible of Youngina capensis (Sauropsida, Diapsida) based on synchrotron tomography, and the phylogenetic implications |journal=Papers in Palaeontology |language=en |volume=9 |issue=5 |doi=10.1002/spp2.1521 |issn=2056-2799|doi-access=free }} The braincase anatomy was redescribed in 2010.{{cite journal |last1=Gardner |first1=Nicholas M. |last2=Holliday |first2=Casey M. |last3=O'Keefe |first3=F. Robin |year=2010 |title=The Braincase of Youngina capensis (Reptilia, Diapsida): new insights from high-resolution CT scanning of the holotype |journal=Palaeontologia Electronica |volume=13 |issue=3 |pages=19A |url=https://palaeo-electronica.org/2010_3/217/217.pdf }} 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, it was probably immobile, similar to the skull of the tuatara,{{cite journal |last=Johnston |first=P. |year=2010 |title=The constrictor dorsalis musculature and basipterygoid articulation in Sphenodon |journal=Journal of Morphology |volume=271 |issue=3 |pages=280–292 |doi=10.1002/jmor.10797 |pmid=19806656 |s2cid=32965233 }} contrary to some earlier claims made about the metakinetic mobility of basicranial joints in Youngina and other early diapsid reptiles.{{cite journal |last=Evans |first=S. E. |year=1980 |title=The skull of a new eosuchian reptile from the Lower Jurassic of South Wales |journal=Zoological Journal of the Linnean Society |volume=70 |issue=3 |pages=203–264 |doi=10.1111/j.1096-3642.1980.tb00852.x |doi-access=free }}

Phylogeny

Youngina was once thought to be closely related to Acerosodontosaurus, and more distantly to tangasaurids (Kenyasaurus, Hovasaurus, Thadeosaurus, and Tangasaurus), but the monophyly of {{notatypo|younginiforms}} has not been demonstrated in published analyses of diapsid reptiles, and it is likely this group is paraphyletic. Acerosodontosaurus is probably closer to other former {{notatypo|younginiforms}}, rather than being closely related to Youngina.{{cite journal |last1=Bickelmann |last2=Müller |last3=Reisz |year=2009 |title=The enigmatic diapsid Acerosodontosaurus piveteaui (Reptilia: Neodiapsida) from the Upper Permian of Madagascar and the paraphyly of "younginiform" reptiles |journal=Canadian Journal of Earth Sciences |volume=46 |issue=9 |pages=651–661 |doi=10.1139/E09-038 |bibcode=2009CaJES..46..651S }} Below is a cladogram from the analysis of Reisz et al. (2011) showing the phylogenetic position of Youngina among early diapsids:{{cite journal |first1=Robert R. |last1=Reisz |first2=Sean P. |last2=Modesto |first3=Diane M. |last3=Scott |year=2011 |title=A new Early Permian reptile and its significance in early diapsid evolution |journal=Proceedings of the Royal Society B |volume=278 |issue=1725 |pages=3731–3737 |doi=10.1098/rspb.2011.0439 |pmid=21525061 |pmc=3203498}}