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. It was first defined in the modern sense by Joyce and colleagues in 2004. 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. ==Classification==