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.

Proganochelys skull tracing from Gaffney 1990 (line art).
Color tracing of elements differ in some regards.

Proterochersis robusta (Fraas 1913, Szczygiellski and Sulej 2016; ZPAL V.39/48) is a Late Triassic German dome-shelled turtle, known from a headliess, limbless, tailless torso/shell, very much like that of extant turtles.

Palaeochersis talampayensis (Rougier et al. 1995; Late Triassic) is a South American sister to Proganochelys.

Baur G 1887. On the phylogenetic arrangement of the Sauropsida: Journal of Morphology, v. 1, n. 1:93-104.

Fraas E. 1913. Proterochersis, eine pleurodire Schilderöte aus dem Keuper. Jahreshefte des Vereins für Vaterlänzische Naturkunde in Württemberg 69: 13–30.

Gaffney ES 1990. The comparative osteology of the Triassic turtle Proganochelys, Bull. Am. Mus. Nat. Hist. 194: 1–263.

Rougier GW, de la Fuent and Arcucci AB 1995. Late Triassic turtles form South America. Science 268:855–858.

Sterli J, de la Fuente MS and Rougier GW 2007. Anatomy and relationships of Palaeochersis talampayensis, a Late Triassic turtle from Argentina. Palaeontographica Abt. A 281:1–61.

Szczygiellski T and Sulej T 2016. Revision of the Triassic European turtles Proterochersis and Murrhardtia (Reptilia, Testudinata, Proterochersidae), with the description of new taxa from Poland and Germany. Zoological Journal of the Linnean Society 177:395-427.

wiki/Proganochelys