Proganochelys quenstedti (Baur 1887) Norian, Late Triassic ~210 mya, 100 cm in length, was, for over a hundred years, the oldest and most primitive turtle known. Derived from a sister to Stephanospondylus and Sclerosaurus, Proganochelys was a sister to Odontochelys and Chelonia and a distant sister to the horned turtles Elginia and Meiolania.
LikeStephanspondylus, Proganochelys retained anteriorly directed nares, a taller skull, especially posteriorly, and a high maxilla. Proganochelys had no maxillary or dentary teeth. The squamosal and quadratojugal fused or the squamosal was reduced to the posterior rim of the skull. Like Stephanospondylus, Proganochelys retained a wide skull without a pinched rostrum. Unlike Stephanospondylus and Odontochelys, Proganochelys widened the skull roof so that the orbits were no longer visible in dorsal view. The postparietals were fused to the parietals.
Proganochelys had a carapace formed by expanded ribs covered by dermal ossicles covered by thick scales. The cervicals and caudals were both armored with sharp dermal ossicles. The posterior tail vertebrae fused to become a club.
The acromion process of the scapula was more developed and the coracoid was fused to the scapula. Some of the metacarpals were shorter than the unguals. The phalanges were reduced to two (including the ungual) for each digit.