Fossil hunter spent five years digging for skull of pliosaur sea monster

An artist's impression of a pliosaur catching a pterosaur

He returned alone to the same cliff almost every day for five years, sifting through the rocks on the shore. But when his work was done, Kevan Sheehan had pieced together one of the most remarkable fossils ever discovered: the 2.4m-long (7ft 8in) skull of a ferocious prehistoric sea monster.

The skull, found on the Jurassic Coast in Dorset, belongs to a pliosaur, a marine reptile that lived about 140 million years ago and was so powerful it could have bitten a car in half, according to scientists.

Between 2002 and 2007, Mr Sheehan, an amateur fossil collector, gathered about 25 large pieces of the fossil. Three other significant pieces have been contributed by other local collectors, leaving just one fragment missing from the front of the jaw.

The erosion on the foremost section of the skull suggests that the missing piece may have dropped away from the cliff 40 to 50 years ago. It could then have been washed away to obscurity.

But tantalising scientific references in the literature on pliosaur specimens found at the same location suggest it may have been picked up by a fossil collector.

“The missing tip of the jaw is turning into something of local legend,” said Richard Edmonds, the earth science manager for the Jurassic Coast. The whole dinosaur would have been about 20m (65ft) in length and weighed up to 12 tonnes (13 tons).

Richard Forrest, a pliosaur expert, said: “Seeing this thing in the flesh, so to speak, is just jaw-dropping. It is simply enormous and monstrous. It could have taken a human in one gulp; in fact, a T. rex would have been breakfast for a beast like this.”

Pliosaurs had short necks and huge, crocodile-like heads that contained powerful jaws and a set of huge, razor-sharp teeth. They used four paddle-like limbs to propel their bulky bodies through the water, and would have preyed on dolphin-like ichthyosaurs and even other pliosaurs.

Despite the gigantic proportions of the specimen and Mr Sheehan’s dedication to gathering the pieces, it was not immediately obvious to him what he had discovered.

He picked up the first fragments of the fossil in 2002 and returned almost daily for the next five years collecting pieces as they fell from the cliff in landslides and rock falls.

A year into his project, Mr Sheehan contacted a group of palaeontologists from Dorset County Council.

“I first met Kevan in 2003 and he just had a big pile of bones. He didn’t realise that it belonged to a single fossil, but I was like, ‘Oh my God, I know what it is!’,” said Mr Edmonds. “When I saw him a year and a half later he’d carried on amassing the skull. I’m staggered he’s managed to do it.”

Mr Edmonds put Mr Sheehan in touch with a well-known local collector, Steve Etches, who helped to find the precise location on the cliff from where the fossil was falling. Most of the fossil was collected from the beach, but identifying its location in the rock allowed the two fossil hunters to dig out the final part of the skull. Mr Sheehan said: “In 40 years of collecting I have often been green with envy at some of the finds other people have made. But now when someone shows me a find, I can say, ‘That’s not a fossil, this pliosaur, that’s a fossil!’”

Digging out the fossil sped up the laborious collection process but it also entitled the anonymous landowner to claim a share of the fossil’s price tag.

Mr Sheehan, who runs a small café near the site, was forced to sell the fossil because his mother is ill and requires 24-hour care.

After negotiations with Dorset County Council, a price of £20,000 was agreed, to be split equally between Mr Sheehan and the landowner.

After it has been scientifically analysed and prepared, the specimen will be put on display at the Dorset County Museum in Dorchester. The museum is hoping that someone will come forward with the final jaw fragment. However, Mr Etches said he thought the chances of this happening were “pretty remote”.

Dr Martill, palaeobiologist at the University of Portsmouth, described the £20,000 price tag as “an exceptionally good deal” for the museum, but said that a lot of work remained to be done on the fossil before it could go on display.

“It will take at least a year to remove this from the surrounding rock, which will add at least £20,000 to what they have paid,” he said.

However, he said the fossil was extremely rare and in almost pristine condition. The skull is close to complete and is in about 25 large fragments and many smaller pieces. Mr Forrest said that the skull was an especially rare find: “Pliosaur skulls are very big, but not that robust, and you tend to find them crushed flat. What is fantastic about this new skull is that it is pretty much in 3-D and not very distorted.”

The rest of the creature could still be entombed in the cliffs and if so, it will be decades before it is exposed.

Palaeontologists estimate that the entire body of the creature is between 10m and 15m in length. Several different species of pliosaur that have been found in the past, with a range of head-to-body length ratios.

It is unlikely that a major excavation will take place as the body may well be buried elsewhere.

When large marine creatures die they often float for long periods before sinking to the ocean bed. During this period they are scavenged on and frequently the head, which is heavy, falls off first, while the body is buoyed up by the air in the lungs and carries on floating.