A study recently published in the scientific journal Current Biology represents the first in-depth analysis of soft tissues from a fossilized plesiosaur, specifically a 183-million-year-old specimen from the Posidonia Shale in Germany, renowned for its well-preserved fossils, as reported by GoteborgsPosten.
Led by Miguel Marx, a doctoral student at Lund University in Sweden, an international team of researchers studied a rare plesiosaur fossil known as MH7, which remarkably retained traces of soft tissue. "These are iconic animals, and the way we reconstruct them hasn't changed for nearly 200 years, so this is a big update," said Marx, according to The New York Times.
The MH7 fossil, discovered in 1940 near Holzmaden, Germany, had spent about 75 years in storage before being prepared for study in 2020. The skeleton, measuring approximately 4.5 meters in length, is almost completely preserved, providing an unprecedented opportunity for examination, as noted by Scinexx.
Upon detailed analysis, the researchers found that the plesiosaur exhibited a mosaic of smooth skin and scales, with areas of both textures discovered on the tail and the trailing edge of the right front flipper. The smooth skin on the tail likely reduced water resistance, allowing the marine reptile to glide more efficiently through the water and catch fish, as reported by Popular Science.
In contrast, the scaly regions on the flippers could have stiffened the trailing edge like a rudder, enhancing propulsion through the water.
The combination of scaly and smooth skin likely made the plesiosaur more hydrodynamic, aiding in efficient movement while capturing prey. This unique adaptation represents an evolutionary detour for plesiosaurs that runs counter to other ancient marine reptiles like ichthyosaurs and mosasaurs, as Discover Magazine points out.
To uncover these findings, the research team employed various imaging techniques, including transmitted light microscopy, scanning electron microscopy, electron backscatter diffraction, and infrared microspectroscopy, to analyze the molecular makeup of the MH7 fossil, detailed by Popular Science.
"The well-preserved German fossil really highlights the potential for soft tissue in providing valuable insights into the biology of these long-extinct animals," said Marx in a press release, according to Discover Magazine. The tissues of the MH7 fossil were so precisely preserved that researchers could study individual skin cells. In some samples, they could even visualize skin cell nuclei under the microscope.
The researchers believe that this variation in skin texture may be related to different functions. The plesiosaur needed to swim smoothly to catch fish and squid, which the smooth body skin facilitated by providing hydrodynamic conditions. At the same time, it also needed to move on rough sea bottoms, something the scaly flippers made possible, as explained by GoteborgsPosten.
However, some paleontologists are skeptical about the idea that plesiosaurs spent time on the sea floor. "I don't see this animal spending a lot of time on the bottom," said F. Robin O'Keefe, a vertebrate paleontologist at Marshall University who was not involved in the study, according to The New York Times. He believes that plesiosaurs were speedy hunters with a high metabolic rate, stating, "This was an active predator that was really cruising around."
Despite differing opinions on their behavior, the study offers insights into the appearance and locomotion of plesiosaurs, marking a turning point in their study as they proved much more difficult to analyze than other prehistoric marine reptiles. "Our findings help us create more accurate life reconstructions of plesiosaurs, something that has been extremely difficult since they were first studied over 200 years ago," Marx said, according to IFLScience.
Plesiosaurs were large marine reptiles that thrived in the oceans of the Mesozoic era, dominating the seas while dinosaurs ruled the land. Characterized by their long necks and small heads, often compared to those of sea serpents, they had wide, flat bodies, short tails, and four long flippers that allowed them to move efficiently in the water, feeding primarily on fish, as described by SciencePost.
This article was written in collaboration with generative AI company Alchemiq