Pappochelys, meaning “grandfather turtle,” represents an extinct genus of reptile that offers significant insights into the evolutionary lineage of modern turtles. This creature existed during the Middle Triassic period, approximately 240 million years ago, preceding the earliest dinosaurs. Its discovery has provided strong support for understanding the long-debated placement of turtles within the diapsid reptile group.
The significance of Pappochelys lies in its unique features, which bridge gaps in the fossil record. It provides a clearer picture of how the complex turtle body plan, particularly the shell, developed over millions of years. This reptile has helped reshape our understanding of how turtles diversified.
Discovery and Physical Traits
Fossils of Pappochelys rosinae were discovered in 2006 in organic-rich claystone within the Lower Keuper rock group in Vellberg, southern Germany. This rock layer dates to the Ladinian stage of the Middle Triassic, around 240 million years ago. Paleontologists Rainer Schoch and Hans-Dieter Sues formally named and described the genus in 2015, based on more than a dozen fossil specimens.
Pappochelys was a small reptile, up to 20 centimeters (about 8 inches) long. It had a wide body and a long tail, roughly half its total length. The skull was pointed with large eye sockets, and unlike modern turtles, it had small, peg-like teeth in its jaws.
Pappochelys had expanded ribs and gastralia (rib-like bones covering the abdomen), which appear to be early shell precursors. Each rib was flattened into a broad, blade-like structure, similar to features found in Eunotosaurus. The gastralia were tightly packed and, in some areas, had begun to fuse, forming a structure resembling the plastron (belly portion) of a modern turtle’s shell.
Evolutionary Importance
Pappochelys is a transitional fossil, offering insight into the step-by-step development of the turtle shell. Its unique anatomical features provide a link between earlier reptiles and fully shelled turtles. The presence of two pairs of holes in the back of its skull, known as temporal fenestrae, classifies Pappochelys as a diapsid reptile, aligning with molecular data that suggests turtles evolved from diapsid ancestors rather than anapsids, which lack these openings.
It is considered morphologically intermediate between Eunotosaurus (Middle Permian, ~260 million years ago), which had broadened ribs, and Odontochelys (Late Triassic, ~220 million years ago), an early stem-turtle with a more developed plastron. Pappochelys exhibits features from both, such as T-shaped ribs like Eunotosaurus, but also displays partially fused gastralia, a step towards the fully formed plastron seen in Odontochelys.
The discovery of Pappochelys confirms the plastron (belly portion of the turtle shell) formed through the fusion of rib-like structures and parts of the shoulder girdle, a process predicted by embryological research. This fossil evidence illustrates the shell’s development was a gradual process over tens of millions of years, with the ventral (belly) armor evolving before the dorsal (back) carapace. The findings from Pappochelys have clarified the sequence of evolutionary steps in turtle shell formation, demonstrating how complex structures can arise incrementally.
Ancient Habitat and Lifestyle
Fossils of Pappochelys were unearthed from rock formations indicating a lake environment, suggesting a semi-aquatic lifestyle. Its thickened bones may have helped reduce buoyancy, potentially making it a more efficient swimmer.
While Pappochelys had a long tail that might have aided swimming, its anatomy does not suggest a fully aquatic existence or strong swimming adaptations. Histological studies of its limb bones reveal a thick outer wall and a small, open medullary cavity, similar to some terrestrial reptiles and unlike modern aquatic turtles. This suggests Pappochelys might have had a more modestly aquatic or even burrowing lifestyle.
Pappochelys used its tiny, peg-like teeth to feed on small insects and worms, indicating an insectivorous or carnivorous diet. It lived in a tropical environment along the shores of a lake in what is now southern Germany, an ecosystem that also included larger predators like the five-meter amphibian Mastodonsaurus and the six-meter terrestrial croc-relative Batrachotomus.