A newly discovered fossil has provided fresh insight into the physical characteristics of plesiosaurs, the serpentine-necked, four-flippered marine reptiles that dominated the oceans during the Jurassic period. The remarkable find reveals that at least some plesiosaurs sported scales on their flippers, similar to those seen on modern-day sea turtles, offering new clues about how these ancient predators may have swum or navigated the seafloor.
Plesiosaurs were among the most successful marine predators of their time, with fossils of these creatures found across the globe. However, soft tissue remains are exceedingly rare, with only eight specimens recorded to date. This new analysis, led by Lund University paleontologist Miguel Marx and his team, utilizes advanced microscopy and spectroscopy to uncover unprecedented details about the appearance and adaptation of these marine reptiles.
The fossil, which belonged to a plesiosaur estimated to be around 4.5 meters in length, was originally excavated in 1940 from Holzmaden, Germany. Following its discovery, the specimen was buried for protection during World War II before being stored for decades in a museum.
The team confirmed that the fossil dates back approximately 183 million years, to a time when plesiosaurs were especially abundant in Earth’s oceans. These creatures are known to have given birth to live young and breathed air, traits that suggest they may have been warm-blooded. Interestingly, while the skin on the fossil’s tail remained smooth, resembling that of today’s warm-blooded marine animals, a sample from the right foreflipper revealed small, irregular triangular scales.
By comparing these fossilized scales to those of modern animals, the researchers found that they closely resemble the carapace scutes of sea turtles and the scales of mosasauroid marine lizards. The thickness of the plesiosaur’s skin was also found to be similar to that of living sea turtles, suggesting an evolutionary adaptation to their aquatic environment.
Marx and his team propose that these scale-like structures may have served a dual purpose. The scales could have enhanced swimming performance by reducing drag, or they may have provided traction while the plesiosaur moved along the seafloor during benthic grazing. The latter theory is supported by evidence of plesiosaurs “bottom-walking” and feeding on sediment-dwelling snails and crustaceans, with preserved stomach contents further corroborating this behavior.
Additionally, the researchers discovered pigment cells near the surface of the tail skin but not on the tougher flipper skin, which may have been adapted for protection. These pigment cells contain corneous beta-proteins, which are responsible for the hardness and immobility of modern reptile scales.
The findings suggest that, unlike other marine reptiles of the time—such as the more fish-like ichthyosaurs, which lost their scales to reduce drag—plesiosaurs retained their reptilian scales after transitioning from land to sea. The researchers conclude that these flipper scales likely provided a selective advantage, contributing to the plesiosaur’s long-term success as one of the most dominant marine predators of the Mesozoic era.
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