Plesiosaurs like this one were evolutionarily suited to aquatic hunting. Credit: Deposit PhotosShareScaly or smooth? That has long been one of paleontologys enduring questions about the plesiosaur. While experts know details about its diet, size, and general habitat, the aquatic reptiles skin characteristics have remained a mystery. But for the first time ever, researchers at Swedens Lund University have analyzed a rare plesiosaur specimens fossilized soft tissue samples, and now believe they can finally answer the decades old question: In actuality, the 183-million-year-old dinosaur relatives skin had a bit of both.The classic life reconstruction of plesiosaurs (Plesiosauria), incorporating a long neck, compact body, and four propulsive flippers, has not changed for nearly 200 years. However, the actual external appearance of these famous Mesozoic reptiles is largely unknown, explained the team in their paper published on February 6th in the journal, Current Biology.MH7 and various microscopic imaging scans taken of its fossilized soft tissues. Credit: Marx, et al. Paleontologists have previously examined fossilized soft tissues from other prehistoric marine reptiles, including ancient sea turtles and ichthyosaurs. With only around eight known fossil tissue samples to date, plesiosaurs have proven much more difficult to study. As New Scientist explained on Thursday, this is especially true given that most examples belong to museums that prohibit the use of potentially destructive imaging tools. But paleontologists finally got their chance with a fossil set known as MH7although it took years to get to that point.MH7s 85-year-journey from excavation to laboratory analysis began in 1940, when German paleontologists first discovered its fossils inside a quarry. Due to the ongoing dangers of World War II, MH7 was subsequently reburied in a garden to protect it from accidental damage. Researchers exhumed the fossils yet again after the end of the war, but this time transported them into safekeeping at Urwelt-Museum Hauff in the nearby town of Holzmaden.In 2020, the Lund University paleontologists finally arranged to assemble and prepare the 183-million-year-old, 11.5-foot-long MH7 for its first-ever detailed tissue examination. Researchers first treated and sterilized thin sections of fossil using a mixture of ultrapure water and ethanol. They then placed the demineralized samples onto slides, and examined the selections using techniques including transmitted light microscopy, scanning electron microscopy, electron backscatter diffraction, and infrared microspectroscopy. Get the Popular Science newsletter Breakthroughs, discoveries, and DIY tips sent every weekday. By signing up you agree to our Terms of Service and Privacy Policy.The team originally theorized the skin might possess the dolphinlike, scaleless qualities of an ichthyosaur, but were surprised at what they found: areas of both scaly and smooth skin. More specifically, it appears that its flippers featured scaly sections, while the rest of its body and tail was scaleless. Researchers theorize the textured flippers allowed the animal to better move along the seafloor while hunting for prey, and the smoother portions reduced drag while swimming. Taken altogether, its likely that plesiosaur skin looked like a mixture of what can be found on todays green sea and leatherback turtles.Its a combination that paid off for the plesiosaur. Although the tail skin suggests a smooth body, the scales along the trailing edges of the flippers undoubtedly fulfilled some functional role, the team wrote, adding that the overall anatomy conferred a selective advantage for plesiosaurs during their protracted evolution as one of the most successful ancient flippered reptiles.