There are approximately 300 extant species and 97 genera of testudines, split into two suborders: the Cryptodirans and the Pleurodirans.
The Pleurodirans, also called the side-necked turtles, have long necks, and fold them sideways to align them with the shell.
[1][failed verification][dubious – discuss] Reptiles are classified according to the pattern of fenestration in the temporal region of the skull.
In these early fossils (mostly of the genus Proganochelys), the teeth have already been lost, and a keratin beak is suggested by the mandibles.
Important differences between Proganochelys and modern turtles are the presence of the palatal teeth (lost in modern species), the inability to retract the head within the shell, and the lack of a trochlear pulley in the jaw closing anatomy.