The Scunthorpe Pliosaur – A Lucky Find

Rose Nicholson, Heritage Manager

The Scunthorpe Pliosaur was discovered in a North Lincolnshire quarry in October 2017 by Darren Withers during a Stamford and District Geological Society field trip. Having previously visited the quarry, the group knew there would be fossils to find, perhaps even a marine reptile bone or two if they were lucky.

The finder of the Scunthorpe Pliosaur, Darren Withers of the Stamford and District Geological Society keeping an eye on the excavation. Courtesy of Darren Withers and Richard Forrest.

A Pliosaur is Not a Dinosaur!

Pliosaurs were the top predators in the seas that formed the Kimmeridge Clays. They lived from the Middle Jurassic until the Lower Cretaceous, around 175 to 100 million years ago. Pliosaurs are rare fossils and finding just a single tooth or bone would be a highlight for a collector.

Pliosaurs were a type of short-necked plesiosaur with large heads, four flippers and incredibly powerful jaws delivering an awesome bite. With snouts packed with sensory organs, good eyesight and a system in their skull which could taste water they were very capable predators. We commonly find bite marks on ichthyosaur and plesiosaur bones that match their teeth and tell us that pliosaurs ate other large marine reptiles as well as other sea creatures.

Millions of years ago pliosaurs were the top predators in the Jurassic and Cretaceous Seas. Here we see a large Pliosaurus about to swallow an unlucky Colymbosaurus, a type of long-necked plesiosaur. Artwork Copyright © Nicholls/Paleocreations 2009.

Pliosaurs range in size from fairly small to as much as 15m long. When alive, the Scunthorpe Pliosaur would have been a fearsome sight at about 8m from snout to tail.

Marine reptile specialists are currently studying the Scunthorpe Pliosaur bones to determine which kind of pliosaur it was when alive. Until that work is complete, the best identification is Pliosaurus sp.

Discovery

On that Saturday in October 2017, CEMEX had granted the group quarry access for 4 hours. After spending some time looking at the quarry floor, Darren decided to investigate some of the stepped banks in the quarry side. He followed a trail of small Rasenia cymodoce ammonites until they petered out after about 30m. Rasenia cymodoce is a zonal ammonite which helps to identify the Pliosaur’s stratigraphic position as the cymodoce zone of the Lower Kimmeridge Clay.

Darren Withers followed a trail of small Rasenia cymodoce ammonites to find the Scunthorpe Pliosaur. Courtesy of Darren Withers and Richard Forrest.

Darren decided to go a little further, and in his own words, “I’m so glad I did because the next thing I was looking down at was a large vertebra”.

The first pliosaur vertebra found by Darren Withers in October 2017. Courtesy of Darren Withers and Richard Forrest.

That day a small number of bones were found, including two vertebrae and the tip of the pliosaur’s snout.

Return and Recovery

With the help of a digger and driver supplied by the quarry, members of the Stamford and District Geological Society returned to fully excavate the area of the find in July 2018. The hope was to recover any remaining bones. These field trips uncovered a humerus, more vertebrae and ribs. In total 28 vertebrae were found, plus ribs, a humerus, a tooth, the atlas / axis complex, a neural spine and the tip of the snout.

When working in a quarry, geologists must abide by health and safety rules: long sleeved high-vis tops and hard hats at all times. Courtesy of Darren Withers and Richard Forrest.

The dig team from left to right: John Green, Darren Withers, Mick Beeson, Paul Hildreth and Michael Oates. Courtesy of Darren Withers and Richard Forrest.

Courtesy of Darren Withers and Richard Forrest.

Marine reptiles found in quarries are usually discovered when excavation machinery removes part of the skeleton. It is probable that parts of the Scunthorpe Pliosaur were lost to quarrying before it was found by Darren Withers.

Plan showing the bones found in relation to each other. Courtesy of Richard Forrest.

The Kimmeridge Clay in which the skeleton was found had kept the bones wet. Exposure to the air could quickly lead to them drying out and disintegrating. The ribs were soaked in a weak paraloid in acetone mixture and then reinforced with plaster jackets before lifting.

The bones were excavated systematically to record as much information as possible. Courtesy of Darren Withers and Richard Forrest.

All the bones were numbered, marked on a plan, and photographed before careful lifting. Courtesy of Darren Withers and Richard Forrest.

Lifting one of the ribs in its plaster jacket. Courtesy of Darren Withers and Richard Forrest.

After lifting the bones required conservation to stabilise them and stop them crumbling away. The conservation work by Nigel Larkin has been funded by generous grants from the Geologists Association’s Curry Fund and the Yorkshire Geological Society.

Kimmeridge Clay

The Pliosaur was found in a band of Kimmeridge Clay. The Kimmeridge Clay Formation is a fossiliferous band of mudstone. It was originally the muddy bed of the sea that covered North Lincolnshire during the Later Jurassic and Early Cretaceous.

The bands of Ferriby Chalk and Carstone Formation above the Kimmeridge Clay. The people stood on a bank in the side of the quarry are near where the Scunthorpe Pliosaur was found. Courtesy of Paul Hildreth.

The Kimmeridge Clay is packed full of fossils. As well as the Pliosaur, the dig team collected fossils including various ammonites and these two bivalves. Top Deltoideum delta bivalve, and bottom Pholadomya sp.

Bivalve Deltoideum delta. Courtesy of Darren Withers and Richard Forrest.

Bivalve Pholadomya sp. Courtesy of Darren Withers and Richard Forrest.

The Scunthorpe Pliosaur’s Story

The systematic excavation of the Scunthorpe Pliosaur’s skeleton means it is possible to explore the taphonomic history of the carcass.

After death, the pliosaur’s body either sank straight to the sea floor or floated for a while bloated by decay gases before bursting and sinking. The positions of the vertebrae and ribs show that the carcase then collapsed on the sea floor rather than being scattered by water movement or scavengers. It was colonised and eaten by bottom-living animals such as sea urchins and oysters. Over millennia sediments covered the bones and turned into the Kimmeridge Clay.

We can explore the story of how the skeleton arrived on the sea floor and what happened to the skeleton as it decayed and was colonised by oysters and other epifauna, animals that live on the seabed.