Scientists Discover Fish-Like Marine Reptile Buried in Its Own Fat 150 Million Years Ago

Sick ichthyosaur. Credit: Esther van Hulsen

A recent study published in PeerJ examines the preservation of unique ichthyosaur fossils using cutting-edge research methodologies. In the final large group of ichthyosaurs, a whole animal and a tail were the first to retain the outer body shape.

Two key terms to remember:

ichthyosaurs were marine reptiles that lived during the time of the dinosaurs. Their fossils have been found all over the world and they are known to have a fish-like shape similar to modern dolphins.

the Solnhofen southern region of Germany is famous for its end Jurassic fossils, which include Archeopteryx, often thought to be the first bird, and countless other species, many of which have been preserved with soft tissue in addition to bones and teeth, which is unusual in the fossil record.

The new peer-reviewed paper reports two 150-million-year-old ichthyosaur fossils from the Solnhofen area. They are kept at Bishops Seminar Eichstätt’s Jura-Museum. An ichthyosaur is a complete specimen, containing an internal skeleton and an outline of soft tissue surrounding the body. The other fossil is a complete caudal fin. The tail vertebrae and the soft tissue surrounding it have been preserved, establishing that ichthyosaurs in this group possessed moon-shaped tails like their ancestors.

A multidisciplinary team of scientists conducted the study. Lead author Lene Liebe Delsett and Jørn Hurum have been working with marine reptiles at the Natural History Museum in Oslo, Norway for several years. Martina Kölbl-Ebert, wildlife specialist from Solnhofen, helped them. They also collaborated with mineralogist Henrik Friis, who analyzed the soft tissue samples to determine what was in them.

Large Ichthyosaur in normal and UV light

Large ichthyosaur in normal and UV light. Credits: Lene L Delsett

The complete specimen is really what makes this project unique as it tells a complete story. Ichthyosaurs are not common as fossils in Solnhofen, which at the time was a relatively shallow area with many islands, whereas ichthyosaurs were inhabitants of the open ocean. It is not known why this one entered the lagoons, but that may be the reason why he died. Seeing the specimen is impactful because it is clearly a complete dead animal body, where we can see its shape due to unique preservation, Delsett says.

During or after death, the ichthyosaur landed on its back and side on the seabed and was covered in fine sediment. Little oxygen and a lot of luck preserved it until it was discovered and excavated in 2009. In the article, the scientists give a first description of the specimen and begin the process of understanding its soft tissues. To do this, they took small samples of the soft tissues of the tail and examined them using X-ray crystallography and a scanning electron microscope. Because the skeletons and the rock in which they are preserved have almost the same color, UV light was used to study the shape of the bones in order to understand what type of ichthyosaur it is. They found that the phosphate found in the tissues of ichthyosaurs likely contributed to preservation. It is not yet possible to identify all types of fossilized tissue in the ichthyosaur, but the new study confidently confirms the preservation of skin and possibly connective tissue. However, most of the material surrounding and covering the specimen is probably decomposed fat.

We know from previous research that ichthyosaurs probably had a blubber, like whales do today. Our research confirms this, for a group of ichthyosaurs where it has not been certain. Another strong similarity between whales and ichthyosaurs is blubber, in addition to their body shape. In the future, I hope these two ichthyosaurs from Solnhofen can be used to improve our understanding of swimming because they preserve the shape of the tail and the body, says Delsett.

Reference: “The Soft Tissue and Skeletal Anatomy of Two Late Jurassic Ichthyosaur Specimens from the Solnhofen Archipelago” by Lene L. Delsett?, Henrik Friis, Martina Kölbl-Ebert, and Jørn H. Hurum, April 7 2022, PeerJ.
DOI: 10.7717/peerj.13173

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