Niolamia argentina (Ameghino 1899; Sterli and de al Fuente 2011; Eocene, 40 mya) was similar to Elginia in having large suproatemporal and even larger tabular horns, but lacked teeth, as in living turtles. This is the basalmost turtle.

Meiolania platyceps (Owen 1886, Gaffney 1983, AM F:57984, Oligocene to Holocene, only 2000 years ago, skull width 60 cm) is famous as the horned turtle with a club tail. It could not withdraw its head and neck into its shell. Derived from Bunostegos and a sister to Elginia represents a distinct basal turtle clade separate from Proganochelys, Chelonia and living turtles. Like pareiasaurs, Meiolania rotated the tabular to the dorsal skull roof. Like pareiasaurs, Meiolania had only six cervical vertebrae with unfused ribs.

What looks like a lateral fenestra is the result of the supratemporal growing down to meet the quadratojugal while leaving the stapes and ear drum unarmored. Not all Meiolania species have this trait. Note the different labels and extents applied to the bones. The lacrimal retains a connection to the naris, unlike living turtles.

The humerus is oriented laterally, as in basal tetrapods, unlike other hard shell turtles, which rotate the elbow anteriorly.

Ameghino F 1899. Sinopsis geológica paleontológica. Suplemento (adiciones y correcciones). Censo Nacional, La Plata:1–13.

Gaffney ES 1983. The cranial morphology of the extinct horned turtle, Meiolania platyceps, from the Pleistocene of Lord Howe Island, Australia. Bulletin of the AMNH 175, article 4: 361-480.

Gaffney ES 1985. The cervical and caudal vertebrae of the cryptodiran turtle, Meiolania platyceps, form the Pleistocene of Lord Howe Island, Australia. American Museum Novitates 2805:1-29.

Gaffney ES 1996. The postcranial morphology of Meiolania platyceps and a review of the Meiolaniidae. Bulletin of the AMNH no. 229.

Owen R 1882. Description of some remains of the gigantic land-lizard (Megalania prisca
Owen), from Australia. Part III.Philosophical Transactions of the Royal Society London, series B, 172:547-556.

Owen R 1888. On parts of the skeleton of Meiolania platyceps (Owen). Philosophical Transactions of the Royal Society London, series B, 179: 181-191.

Sterli J and de la Fuente M 2011. Re-Description and Evolutionary Remarks on the Patagonian Horned Turtle Niolamia argentina Ameghino, 1899 (Testudinata, Meiolaniidae). Journal of Vertebrate Paleontology. 31 (6): 1210–1229.