A Middle Triassic stem-turtle and the evolution of the turtle body plan

The Pappochelys sample preserves broadened ribs and robust paired gastralia without a fused plastron or complete carapace; proposed gastral fusion and its position among sampled stem turtles are homology and topology hypotheses, not a linear ancestral stage.

The documented turtle-line samples include Odontochelys from Late Triassic marine deposits in southwestern China and Pappochelys from the Middle Triassic Vellberg deposits of Germany; these named localities do not establish a global Testudines distribution.

The cited turtle-line sample records complementary shell mosaics: Odontochelys has a developed plastron, expanded ribs and neural plates without a complete carapace, whereas Pappochelys has broadened ribs and robust paired gastralia without a fused plastron or complete carapace.

Li et al. interpret the marine deposits yielding Odontochelys as marginal sea or river-delta settings, while the cited Pappochelys shell study addresses anatomy and shell evolution; these observations do not establish diet, body size or a single ecological guild for Testudines.