Testudinata is the group of all tetrapods with a true turtle shell. It includes both modern turtles (Testudines) and many of their extinct, shelled relatives (stem-turtles), though excluding Odontochelys and Eorhynchochelys, which are placed in the more inclusive Pantestudines.
It was first coined as the group containing turtles by Jacob Theodor Klein in 1760. In 1832-1836, Thomas Bell wrote a book describing the Testudinata, which summarizes all the world's turtles, living and extinct, illustrated by forty plates by Jane S. Bell, James de Carle Sowerby and Edward Lear.[1] It was first defined in the modern sense by Joyce and colleagues in 2004.[2] While the ancestral condition for the clade is thought to be terrestrial, members of the subclade Mesochelydia, which contains almost all known testudinatans from the Jurassic onwards, are thought to be ancestrally aquatic.[3]
The cladogram below follows an analysis by Jérémy Anquetin in 2012.[2]