Youngina is known from several specimens. Many of these were attributed to as separate genera and species (such asYoungoides andYoungopsis), but it was later realized that they were not distinct fromY. capensis.[2][3] Theholotype specimen ofYoungina, discovered byBroom himself,[2] was described briefly in1914.[4] The "Youngoides romeri" specimen was first attributed toYoungina,[5] but later given its eponymous and separate designation in a later paper.[6]Acanthotoposaurus[7] is also ajunior synonym ofYoungina.[8]
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).[9] Thebraincase anatomy was redescribed in 2010.[10]Youngina shows a mosaic of features found in more primitive diapsids and more derived taxa such asarchosauromorphs andlepidosauromorphs suggesting a non-orthogenetic evolution of these characters. Though the palatobasal articulation is open,[10] it was probably immobile, similar to the skull of thetuatara,[11] contrary to some earlier claims made about the metakinetic mobility of basicranial joints inYoungina and other early diapsid reptiles.[12]
Youngina was once thought to be closely related toAcerosodontosaurus, and more distantly totangasaurids (Kenyasaurus,Hovasaurus,Thadeosaurus, andTangasaurus), but the monophyly of 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 formeryounginiforms, rather than being closely related toYoungina.[13] Below is acladogram from the analysis of Reiszet al. (2011) showing thephylogenetic position ofYoungina among early diapsids:[14]
^abGow, C. E. (1975). "The morphology and relationships ofYoungina capensis Broom andProlacerta broomi Parrington".Palaeontologia Africana.18:89–131.hdl:10539/16290.
^Evans, S. E. (1987). "The braincase ofYoungina capensis (Reptilia: Diapsida; Permian)".Neues Jahrb. Geol. Paläontol. Monats.1987:193–203.
^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.JSTOR1298390.
^Johnston, P. (2010). "The constrictor dorsalis musculature and basipterygoid articulation inSphenodon".Journal of Morphology.271 (3):280–292.doi:10.1002/jmor.10797.PMID19806656.S2CID32965233.
^Bickelmann; Müller; Reisz (2009). "The enigmatic diapsidAcerosodontosaurus 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.
