A Welsh Ichthyosaur

A Welsh Ichthyosaur, preparation from the reverse side.

Ichthyosaur somersetensis

At the end of July, I was given a partial Ichthyosaur to prepare, which had been found on the Welsh coast. It was clear that the specimen had been subject to the harsh erosive conditions of the coast during recent exposure, coupled with similar conditions before or during preservation approximately 205 million years ago.

The above image shows the associated bones. The yellow lines on the matrix are as a result of sea water penetrating the rock, softening it and gradually destroying the fossil.

Here, where the tip of the rostrum is separated, a fault line has been eroded through leaving a 2 cm gap in the jaws.

Above: The back part of the Ichthyosaur skull with the prominent ‘V’ shape of the jaws tapering towards the front of the skull. Top left in this photo is the humerus and paddle from the front flipper.

Above: Mostly dis-articulated front paddle and end of humerus.

This specimen, like several I have seen, displayed scattered and dis-articulated bones on the top side (exposed side on the sea floor), yet under the dis-articulated bones, the jaws and opposite side of the skull appear articulated. This side (underside) would have been protected by the soft silt etc on the sea floor whilst the top, exposed side would have been at more risk of disturbance by the sea, current & predation from scavengers and predators.

Above: The Ichthyosaur skull as found. Much of the matrix around the fossil was removed due to its delicate nature.

 

Start of Preparation

The Somerset and Welsh marine reptile preservation, that I have seen, tends to have a lot of material compacted in with the sedimentation in the form of shells and sea urchins. This can sometimes be the result of the sea creatures feeding on the dead animal or just an abundance of them already on the sea floor. It however makes the preparation a great deal trickier as they form calcitic barriers between the delicate fossil and the rock, which has to be carefully dug through with fine pneumatic tools right down to the last 10th of a millimeter above the fossil.

 

Above: A small area of the skull is covered with fibreglass resin to strengthen the area before the under side can be prepared. At this stage it is just to check whether the skull is as articulated, as hoped, before committing to a time consuming preparation job.

Above: The skull appears to be intact with articulated teeth – a good sign that the preparation should be undertaken. Also evident is a thin white layer and pyritic & calcareous layer above and covering the bone.

I continue to remove the rock from the bone to get an overall impression of the articulation before I start working on the more detailed areas.

The darker fine layers on the surface of the skull have a high pyrite content which makes it difficult to remove. So fine air chisels are used rather than the air abrasive.

 

The fossil starts to take shape, even the delicate sclerotic eye ring that supported the Ichthyosaurs large eye is in place.

I add the tip of paddle and prepare the tip of rostrum from the underside, then attach the rostrum and loose associated paddle bones. I also replace the missing areas with resin details to give the impression of a complete skull. I continue to clean the details of the skull and add a resin surround to greatly strengthen and protect the fossil.

The fossil is finally finished.

All the processes used are reversible if needed to be taken apart in the future, but otherwise the fossil is set in a solid frame which should last for many years.

 

Total preparation time from start to finish 70 hours.