Eunotosaurus africanus (Seeley 1892) Middle Permian ~15 cm snout to vent length, was considered by Watson (1914) as the ancestor to the turtle because of its wide ribs and low number of dorsal vertebrae. The present study nests turtles with Stephanospondylus and the wide ribs find their origins in the less wide ribs of Milleretta RC14. Derived from a sister to Acleistorhinus, Eunotosaurus left no known descendent taxa.

Distinct from Acleistorhinus, the skull of Eunotosaurus enlarged the naris and orbit and reduced the jugal. A long retroarticular process developed on the mandible by expansion of the articular. The quadratojugal is reduced to just the quadrate portion.

Distinct form Milleretta RC14, the number of dorsal vertebrae was greatly reduced and each rib was greatly expanded in width and individually as well. The sacral vertebrae were reduced to one. The long slender tail, seen here beneath the torso, was longer than the presacral length.

The scapulocoracoid was fused. The humerus was larger and larger than the femur. The radius and ulnas sere surprisingly slender.

The ilium was taller.

Eorhynchochelys sinensis (Li et al. 2018; Late Triassic) was considered the earliest known stem turtle with a toothless beak, but here nests as a giant aquatic eunotosaur with tiny premaxillary teeth. In size and overall build it converges with Cotylorhynchus.

Microleter mckinzieorum (Tsuji et al. 2010, Early Permian, 3 cm long skull) was considered a basal parareptile (an invalid clade). The large reptile tree nests Microleter with Acleistorhinus, Eunotosaurus and Delorhynchus. Distinct from these taxa, Microleter has a larger orbit and narrower skull.

Watson DMS 1914. Eunotosaurus africanus (Seeley) and the ancestors of the Chelonia, Proceedings of the Zooogical Society of London 11:1011–1020.

Cisneros JC, Rubidge BS, Mason R and Dube C 2008. Analysis of millerettid parareptile relationships in the light of new material of Broomia perplexa Watson, 1914, from the Permian of South Africa. Journal of Systematic Palaeontology 2008 (6): 453–462. doi:10.1017/S147720190800254X

Cox CB 1969. The problematic Permian reptile Eunotosaurus. Bulletin of the British Museum of Natural History 18: 167–196.

Keyser AW and Gow CE 1981. First complete skull of the Permian reptile
Eunotosaurus africanus Seeley. South African Journal of Science 77: 417–420.

Gow CE 1997. A reassessment of Eunotosaurus africanus Seeley (Amniota: Parareptilia). Palaeontologia Africana, 34:33–42.

Gow CE and de Klerk B 1997. First record of Eunotosaurus (Amniota: Parareptilia) from the Eastern Cape. Palaeontologia Africana, 34: 27–31.

Lyson TR, Bever GS, Bhullar B-AS, Joyce WG, Gauthier JA 2010. Transitional fossils and the origin of turtles. Biology Letters 6:830-833. online PDF

Modesto SP 2000. Eunotosaurus africanus and the Gondwanan ancestry of anapsid reptiles. Palaeontologia Africana, 36:15–20.

Rubidge BS, Modesto, S, Sidor C and Welman J. 1999. Eunotosaurus africanus from the Ecca–Beaufort contact in Northern Cape Province, South Africa — implications for Karoo Basin development. South African Journal of Science 95: 553–555. online pdf

Tsuji L, Müller J and Reisz RR 2010. Microleter mckinzieorum gen. et sp. nov. from the Lower Permian of Oklahoma: the basalmost parareptile from Laurasia. Journal of Systematic Palaeontology 8 (2): 245–255.

wiki/Eunotosaurus