Scale loss is a quintessential hydrodynamic adaptation in marine reptiles, and paralleled the pelagic specializationsof Mesozoic ichthyosaurs, plesiosaurs, and metriorhynchid crocodylians, as well as the modernLeatherback Sea turtle (Dermochelyidae). By contrast, modern hard-shelled sea turtles (Cheloniidae) retainboth scutes and scaly flippers, despite evolving from among partially scale-less antecedents after the earliestEocene, ∼54 million years (Ma) ago. Here, we resolve the ambiguous ancestry of scale loss using the oldestknown sea turtle (total-group Chelonioidea) soft tissues preserved in a mid-Cretaceous (middle-to-upperCenomanian, ∼97 Ma) protostegid (basally divergent chelonioid) from Lebanon. This fossil combinesscale-less flipper skin with a scuted carapace similar to other extinct chelonioids, but confirms lineage specificrather than ubiquitous scale loss in an ancestral states analysis. Scale-less skin is therefore an ancientsea turtle trait that was repeatedly modified from scaly ancestors within disparate chelonioid clades duringtheir recurrent independent invasions of oceanic environments.