Plesiosaurs are an iconic group of Mesozoic marine reptiles with an evolutionary history spanning over 140 million years (Ma).1 Their skeletal remains have been discovered worldwide; however, accompanying fossilized soft tissues are exceptionally rare.2 Here, we report a virtually complete plesiosaur from the Lower Jurassic (∼183 Ma)3 Posidonia Shale of Germany that preserves skin traces from around the tail and front flipper. The tail integument was apparently scale-less and retains identifiable melanosomes, keratinocytes with cell nuclei, and the stratum corneum, stratum spinosum, and stratum basale of the epidermis. Molecular analysis reveals aromatic and aliphatic hydrocarbons that likely denote degraded original organics. The flipper integument otherwise integrates small, sub-triangular structures reminiscent of modern reptilian scales. These may have influenced flipper hydrodynamics and/or provided traction on the substrate during benthic feeding. Similar to other sea-going reptiles,45678910 scalation covering at least part of the body therefore probably augmented the paleoecology of plesiosaurs.