Temporal range: Late Triassic, 210 Ma
|Skeleton of Proganochelys quenstedti, American Museum of Natural History|
Proganochelys quenstedti is the oldest stem-turtle species with a complete shell discovered to date, known only from fossils found in Germany and Thailand in strata from the late Triassic, dating to approximately 210 million years ago. It has several synonyms, including Chelytherium ("Turtle Beast"), Psammochelys ("Sand Turtle"), Stegochelys ("Roof Turtle") and Triassochelys ("Triassic Turtle").
In life it was about 1 meter long. Its overall appearance resembled modern turtles in many respects: it lacked teeth, likely had a beak, and had the characteristic heavily armored shell formed from bony plates and ribs which fused together into a solid cage around the internal organs. The plates comprising the carapace and plastron were already in the modern form, although there were additional plates along the margins of the shell, that would have served to protect the legs. Also unlike any modern species of turtle, its long tail had spikes and terminated in a club, its head could not be retracted under the shell, and its neck was protected by small spines. While it had no teeth in its jaws, it did have small denticles on the palate.