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The Abingdon Ichthyosaur transformed

Blog post 13th November 2020


Abingdon Museum recently hosted a research visit from two researchers at Portsmouth University, Megan Jacobs and David Martill. They had been in touch to say that they were working on Late Jurassic Ichthyosaurs. Abingdon’s Ichthyosaur skeleton, which was excavated in 1988 at Oday Hill, was of interest to them, and they asked to come and see it.

The Abingdon Ichthyosaur is one of the museum’s star exhibits, so how did it come to be here?

The first indication that there was something interesting to be discovered at the gravel pit at Oday Hill came when a few fossil bones were unearthed in December 1988. Since the gravel extraction work stopped over the Christmas period, local archaeologists had the opportunity to investigate. They soon found many more bones which eventually amounted to most of the front half of an Ichthyosaur.

Drawing of the Abingdon Ichthyosaur bones as they were discovered in the ground: 
the jawbones are on the left, and a mass of scattered ribs on the right. © Abingdon Museum

The name Ichthyosaur is derived from the two Greek words for “fish” and “reptile”. They were marine reptiles with streamlined bodies, flippers, dorsal fins and tails, in shape not unlike dolphins. The first Ichthyosaurs appeared in the Triassic, 250 to 200 million years ago, but they reached their greatest diversity in the Jurassic, 200 to 145 million years ago. Scientists have identified many species of Ichthyosaur, and they were probably plentiful in the seas which covered the Abingdon area during that era. Over time many remains of Ichthyosaurs have been found here, mostly vertebrae. The find at Oday Hill was the only one in Abingdon which yielded such a large part of a single specimen.

The bones were carefully excavated by the archaeologists. The company which owned the gravel pit gave them to the museum. They were put together in their current display case with the help of experts from the Natural History Museum. There they have been admired by many visitors, and if you consider the assembly to be a single object, it is the largest thing on display apart from the MG car.

The bones of the jaws and the shoulders as they were laid out previously. © Abingdon Museum

When the request to view the Ichthyosaur came from the two researchers from Portsmouth University, it had been on display in its case unchanged for years. The first problem that we at the museum had to solve was how to get into the case! Nobody had opened it for years, and there didn’t seem to be any plans or instructions. Luckily we figured it out before the day of the visit!

When the researchers arrived, they were impressed with our specimen and looked forward to getting close to it. We opened the case in sections, and they started their examination with the spine and ribs, working their way towards the jawbones.

Megan Jacobs from Portsmouth University examines and photographs the Ichthyosaur bones. © Abingdon Museum

One revelation came when they were halfway up, looking at the shoulderblades and the forelimbs. As they examined the bones individually, it turned out that two bones had been mis-identified and misplaced. What previous researchers had taken to be the clavicles turned out to be the jugals. These bones sit on the ‘face’ of the Ichthyosaur, underneath the eyes. They have a curved side which indicates the size of the eyes of this animal. We had previously thought that we didn’t have anything of the eyes and so couldn’t tell how big they might have been. Generally speaking Ichthyosaurs have large eyes in proportion to their head, possibly the largest of any animal. Even without doing precise measurements, the researchers could tell that our animal had exceptionally large eyes. David Martill told us that although we always speak of the Jurassic Sea as shallow, it would not have been quite so shallow round here. Our Ichthyosaur probably dived quite deep into regions where very little light penetrated from above, beyond depths of 200 m. When hunting for squid, the huge eyes would have helped it to make use of whatever little light remained in those zones. There is even a theory that Ichthyosaurs had organs with which they could detect electrical impulses, similar to sharks.

The second big change came when they looked at the jawbones. These, they found, had been placed at the wrong sides, so they moved the ones on the left over to the right and vice versa. They also turned them over, so they now lie with the outside upwards. The smaller fragments of bone between them could not be precisely identified, but they are part of the skull, possibly the palate.

The bones of the head as they are laid out now. © Abingdon Museum

Turning the jaw bones over finally revealed a wealth of intriguing details, which have given us a whole new story about our Ichthyosaur. Clearly visible on the bones are bite marks, made by an even larger and more ferocious animal. It looks like something has sunk its teeth into the snout of the Abingdon Ichthyosaur, leaving behind big holes and scratches. The attack probably came from a Pliosaur. These carnivores inhabited the same Late Jurassic marine world as the Ichthyosaur. Pliosaur vertebrae and other fossilized bones have been found in and around Abingdon. Pliosaurs had long snouts with large teeth, and they hunted squid, fish, and other marine reptiles. One of them clearly had a go at our Ichthyosaur, but that was not the cause of its death. A close look at the bone structure showed signs of healing around the injuries on the jaw. This animal survived the attack and got away.

Bite marks on the upper jaw of the Ichthyosaur. © Abingdon Museum

A level-headed museum curator like myself would perhaps dismiss the story of a life-and-death struggle playing out in the sea around Abingdon as a bit fanciful, but it really happened, and here we have the evidence right in front of us.

And finally, it turns out that our Ichthyosaur might not be what we always thought it was. The species had been identified as Ophthalmosaurus icenicus, and that is what we had put onto the label and information panels. However, the two visiting researchers disagreed. They could not tell straight away what our Ichthyosaur should be called instead, but they agreed that it was not an Ophthalmosaurus. They suggested it could even be a new species. Further analysis will have to be done. The researchers went away with notes and photographs, and we await with anticipation what else they can tell us about this specimen.

Next time you are able to see the Abingdon Ichthyosaur, you will notice the new arrangement of the bones which does more justice to the shape and structure of the animal. You will also be able to see the marks on its jaw and imagine the drama which played out right here in Jurassic Abingdon.

By Elin Bornemann, Collections Officer.
Abingdon County Hall Museum

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