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").

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").