Younginidae

Younginidae Temporal range: Late Permian - Early Triassic
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Diapsida
Clade:	Neodiapsida
Family:	†Younginidae Broom, 1914

Younginidae is an extinct family of diapsid reptiles from the Late Permian and Early Triassic. In a phylogenetic context, it is near the base of the clade Neodiapsida. Younginidae includes the species Youngina capensis from the Late Permian of South Africa and Thadeosaurus colcanapi from the Late Permian and Early Triassic of Madagascar. Heleosuchus griesbachi from the Late Permian of South Africa may also be a member of the family.

Younginidae was traditionally assigned to Eosuchia, an order containing an assemblage of basal diapsids now thought to represent an evolutionary grade rather than a true clade. In 1945 paleontologist Alfred Romer reclassified Younginidae within a new group, Younginiformes, grouping it with the families Tangasauridae and Prolacertidae. Romer considered Younginidae to include many genera that are no longer classified as younginids: Paliguana, Palaegama, and Saurosternon are now considered basal lepidosauromorphs, Galesphyrus and Heleosuchus are diapsids of uncertain affinities (incertae sedis), Heleophilus is now a milleretid, and Heleosaurus is now thought to be a varanopid synapsid.^[1][2] Like Eosuchia, Younginiformes is no longer considered valid; for example, the phylogenetic analysis of Reisz et al. place younginids close to Sauria, the clade including the still-living archosauromorph and lepidosauromorph reptiles, while the younginiform family Tangasauridae takes a more basal position in Neodiapsida. Below is a cladogram from that analysis:^[3]

	Captorhinidae Diapsida Araeoscelidia Neodiapsida Orovenator Lanthanolania Tangasauridae Tangasaurus Acerosodontosaurus Hovasaurus Younginidae Thadeosaurus Youngina Claudiosaurus Sauria Archosauromorpha Lepidosauromorpha

References

1. Laurin, M.; Reisz, R.R. (1995). "A reevaluation of early amniote phylogeny" (PDF). Zoological Journal of the Linnean Society. 113 (2): 165–223. doi:10.1111/j.1096-3642.1995.tb00932.x.
2. Reisz, R.R.; Modesto, S.P. (2007). "Heleosaurus scholtzi from the Permian of South Africa: a varanopid synapsid, not a diapsid reptile". Journal of Vertebrate Paleontology. 27 (3): 734–739. doi:10.1671/0272-4634(2007)27[734:HSFTPO]2.0.CO;2.
3. Robert R. Reisz, Sean P. Modesto and Diane M. Scott (2011). "A new Early Permian reptile and its significance in early diapsid evolution". Proceedings of the Royal Society B. 278 (1725): 3731–3737. doi:10.1098/rspb.2011.0439. PMC 3203498. PMID 21525061.