Between the Jurassic and the present: What connects plesiosaurs and turtles
Analysis of the fossil skin of a 183-million-year-old plesiosaur revealed that it had a mixture of smooth and scaly skin.
Artist's impression of the examined plesiosaur with scales on the fins.
(Image: Joschua KnĂĽppe)
An international team of researchers led by scientists from Lund University in Sweden has carried out a detailed study of fossilized soft tissues of a plesiosaur from the Jurassic period. The results show that the marine reptiles had a combination of smooth and scaly skin, which allows conclusions to be drawn about their swimming abilities and way of life. Plesiosaurs were a group of marine reptiles that colonized the oceans during the Mesozoic Era (203 to 66 million years ago). Their fossil remains have been found worldwide, but preserved soft tissue is extremely rare. In total, only eight scientifically documented finds are known to date.
The team examined the fossilized soft tissue of a 183-million-year-old plesiosaur named MH 7, which originated from a quarry near Holzmaden in southern Germany and was excavated back in 1940. The study was published in the journal "Current Biology".
"Fossilized soft tissues such as skin and internal organs are exceptionally rare. We used a wide range of techniques to identify both smooth skin in the tail area and scales on the edge of the fins," says lead author Miguel Marx from Lund University.
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Between manual work and spectroscopy
First, the sensitive tissue remnants were carefully exposed using hand tools and packed in aluminum foil and sterile containers for transport. In the laboratory, they were then thoroughly cleaned with ultrapure water and sterilized with high-percentage ethanol. Before each further analysis, the samples were documented in detail with photographs to record the initial condition.
(Image:Â Klaus Nilkens/Urwelt-Museum Hauff)
According to Marx, a crucial step was the demineralization of the samples, which was carried out in different groups. The fossils were treated in a special EDTA solution (ethylenediaminetetraacetic acid) for several weeks in order to remove the mineral components and expose the organic structures. The samples were prepared for further analysis by careful rinsing with various buffer solutions.
The actual analysis was then carried out using a wide range of state-of-the-art technologies: The researchers combined transmission light microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, electron backscatter diffraction, infrared microspectroscopy and time-of-flight secondary ion mass spectrometry. According to the researchers, this variety of methods enabled them to analyze both the structural details of the fossil skin and its chemical composition.
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Smooth skin on the tail, scales on the fins
The remains showed a remarkably well-preserved skin structure with different layers such as the stratum corneum, stratum spinosum and stratum basale. According to the scientists, even individual keratinocytes with cell nuclei and pigment cells (melanosomes) were still detectable. To their surprise, they discovered a combination of smooth skin on the tail and small, triangular scales on the fins. "The scale-like structures could have stiffened the fins during paddling movements while swimming or protected them while grazing on the seabed," writes Sven Sachs from the Natural History Museum in Bielefeld, who was involved in the study, on Bluesky.
For comparison, the researchers examined other plesiosaur fossils from the region, which also showed soft tissue remains on the fins and evidence of fleshy tail fins. They also analyzed skin samples from modern reptiles such as turtles and monitor lizards. "The exceptionally well-preserved fossils from Germany show the great potential of soft tissue remains for our understanding of the biology of long-extinct animals," emphasizes Marx. He compares the skin of the plesiosaur studied with a mixture of the scaly green sea turtle and the smooth-skinned leatherback turtle.
(vza)
