Characterising a 200 million years old sea dragon

Monday, February 5, 2018 - 15:15
Image: Sir David Attenborough and Bristol University researcher, Fiann Smithwick, at the electron microscope discussing skin pigmentation of the ichthyosaur [Bristol University].
A rotary pumped sputter coater from Quorum has proven instrumental to University of Bristol researchers using SEM to characterise a sea dragon skeleton, aged more than 200 million years. 
The skeleton was discovered by fossil collector, Chris Moore, and is now the subject of a David Attenborough BBC documentary called Attenborough and the Sea Dragon
Reconstruction of the ichthyosaur head [BBC]
The recent discovery in the limestone cliffs west of the village of Lyme Regis turned into a very special find.
The story began with the careful removal of the skeleton embedded in the rocks.
Back in Moore’s laboratory, it was very carefully cleaned with all rock removed to reveal the bones of the sea dragon, or ichthyosaur. 
The final shape and size of the creature had to be predicted from various scientific analyses.
Initial studies were made using computerised tomography at the University of Southampton and the National Veterinary College.
The data was analysed at the University of Bristol from which it was possible to construct a complete ichthyosaur.
Further work on the bones revealed more details of the life and death of this skeleton. 
One very interesting aspect of the characterisation process was made after further removal of rock debris around individual bones of the skeleton.
Samples of skin were carefully scraped away and were analysed at the University of Bristol in the Schools of Earth and Biological Sciences.
As researcher, Fiann Smithwick, says: “Once we had the skin separated, we wanted to image it using SEM to find out about the sub-micron features and try to identify components such as pigments as these would indicate how light or dark the skin of the ichthyosaur was 200 million years ago. "
"However, before we could image the specimen, we had to make it conductive. Fossil samples are normally insulators and are hard to image in an SEM without coating due to a build-up of charge on the surface, which distorts the images," he explains.
To prevent charge build-up, the researchers used a Quorum Q150R ES rotary pumped sputter coater to apply a thin, uniform gold coating to dozens of samples.
Fiann Smithwick uses the Quorum Q150R ES gold coater to prepare the fossilised skin of the ichthyosaur for imaging in the SEM [University of Bristol]
"We were then able to identify 0.5 micrometre structures called melanosomes," says Smithwick. "These are organelles found in animal cells and are the site for synthesis, storage and transport of melanin, the most common light-absorbing pigment found in the animal kingdom."
By looking at samples taken from the top and bottom of the ichthyosaur, we could see that it had lots of pigment on the top, but very little on the underside, suggesting that it had a dark back and light belly," he adds. 
Dorsal back skin with lots of melanosomes [BBC]
The colour pattern - known as countershading - is seen today in animals such as sharks and dolphins but this is the first time it has been reported for an ichthyosaur.
Countershading is thought to act as camouflage in living animals but may also provide protection against UV light and to help regulate body temperature.
As the final reconstruction of a 3D image of the ichthyosaur was completed, it became clear this particular specimen was a previously unknown species having larger front paddles than others.
Overall, the “new” ichthyosaur would have measured nearly 4½ metres.
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