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.
Psammochelys, Stegochelys, and Triassochelys are junior synonyms of Proganochelys. Chelytherium von Meyer, 1863 has been considered a synonym of Proganochelys by some authors, but Joyce (2017) considers it a nomen dubium given the fragmentary nature of the syntype material. Joyce (2017) also considered North American genus Chinlechelys to be a junior synonym of Proganochelys, though the author maintains the type species of the former genus, C. tenertesta, as a distinct species within the genus Proganochelys.
Proganochelys was once considered as the oldest known turtle until the description of Odontochelys, a slightly earlier genus that lived in the Carnian stage of the Triassic. 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.
Proganochelys is considered to have lived in the giant continent Laurasia during the Triassic period. The fossil records show that Proganochelys might have lived anywhere in between Thailand and Germany. During the Triassic period, Laurasia was primarily dry and warm, especially in arid areas. Proganochelys shared their environment with a variety of dinosaurs. Proganochelys lived in small water bodies such as ponds, but it was mainly earthbound.
- Palmer, D., ed. (1999). The Marshall Illustrated Encyclopedia of Dinosaurs and Prehistoric Animals. London: Marshall Editions. pp. 66–67. ISBN 1-84028-152-9.
- Enchanted Learning Paleontology and Geology Glossary
- belated questions about beaks
- Animal Diversity Web: Order Testudines
- A Middle Triassic stem-turtle and the evolution of the turtle body plan
- Transitional fossils and the origin of turtles
- An ancestral turtle from the Late Triassic of southwestern China
- Shell bone histology indicates terrestrial palaeoecology of basal turtles