Extended Data Figure 5: Bayesian tree topology derived from total matrix (50% majority rule consensus).

An exclusive Eunotosaurus–turtle clade is recovered with 100% posterior probability. This pan-turtle lineage is nested within the radiation of anatomically diapsid reptiles; however, in contrast to the parsimony solution, turtles are excluded from crown-group Diapsida. The Bayesian results agree with the parsimony in revealing strong support that: (1) Eunotosaurus is an early stem-group turtle; and (2) the ancestral stem turtle expressed a fully diapsid skull. The two analyses also agree that there is currently poor morphological support for a refined position of turtles within the greater diapsid radiation.