Fossil reveals silent swimmer of the Jurassic deep

Dr Dean Lomax and Dr Johan Lindgren, with fellow researcher Sven Sachs, examining one part of the flipper at Lund University, Sweden. Courtesy of Katrin Sachs.

A new study has uncovered evidence that a giant marine reptile from the early Jurassic period used stealth to hunt its prey in dark waters – similar to how owls fly silently at night.

The research focused on a metre-long flipper fossil of an ichthyosaur, which was uniquely preserved with soft tissue. Scientists were able to examine the intricate structure of the flipper in detail using the advanced imaging techniques of Diamond’s I12 beamline.

The findings, which were published in Nature, suggest that the giant ichthyosaur Temnodontosaurus was equipped with specialised fins that could suppress the sound of its own movements when foraging in dimly lit environments.  

A range of advanced imaging, chemical analysis and computational modelling techniques allowed Dr Johan Lindgren of Lund University and ichthyosaur expert Dr Dean Lomax of the University of Manchester and University of Bristol to make the discovery.

Dr Lindgren, who has pioneered research on ancient marine reptile soft tissues, said: “The wing-like shape of the flipper, together with the lack of bones in the distal end and distinctly serrated trailing edge collectively indicate that this massive animal had evolved means to minimise sound production during swimming. Accordingly, this ichthyosaur must have moved almost silently through the water, in a manner similar to how living owls, whose wing feathers also form a zigzag pattern, fly quietly when hunting at night. We have never seen such elaborate evolutionary adaptations in a marine animal before.”

183-million-year-old soft-tissue fossil (SSN8DOR11; Paläontologisches Museum Nierstein, Nierstein, Germany): an isolated wing-like front flipper of the giant megapredatory ichthyosaur Temnodontosaurus. Courtesy of Randolph G. De La Garza, Martin Jarenmark and Johan Lindgren.

Although many small ichthyosaurs have been found with soft-tissue preservation, scientists have never found anything on this scale. The fossil consists of both the part and counterpart (opposing sides) of almost an entire front flipper. As the top part of the fin is missing, the team surmise that it was originally an isolated flipper that might have been ripped off by a larger ichthyosaur.

To unravel the mystery behind the features preserved in this fossil, it was subjected to a range of sensitive imaging, elemental and molecular analyses. The multidisciplinary research team included palaeontologists, engineers, biologists and physicists. This involved high-end techniques such as synchrotron radiation-based X-ray microtomography at the Swiss Light Source SLS at PSI and Diamond Light Source, time-of-flight secondary ion mass spectrometry and infrared microspectroscopy, along with the reconstruction of a virtual model using computational fluid dynamics.

Dr Lomax added: “The fossil provides new information on the flipper soft tissues of this enormous leviathan, has structures never seen in any animal, and reveals a unique hunting strategy (thus providing evidence of its behaviour), all combined with the fact that its noise-reducing features may even help us to reduce human-made noise pollution. Although I might be a little bias, in my opinion, this represents one of the greatest fossil discoveries ever made.”

To find out more about the I12 beamline, or to discuss potential applications, please contact Principal Beamline Scientist Dr Genoveva Burca, Genoveva.Burca@diamond.ac.uk