Classic fossil site re-explored in undergraduate project

Aust Cliff near Bristol has been known as a rich fossil site since the 1820s. Since then, thousands of people have visited this spectacular location on the banks of the Severn, and collected fossils of ancient sharks and sea dragons.

In a new paper, published today by a team of undergraduates from the University of Bristol, the first detailed account of the ancient ecosystem is presented.

Aust Cliff, which is right next to the First Severn Crossing, first came to the attention of geologists in 1824, when a classic paper was published by William Buckland and William Conybeare.

They rowed out in a boat into the centre of the Severn, and sketched the striking red and grey cliffs, which was later recognised to mark one of the key geological boundaries, showing the contact between the Triassic and Jurassic periods.

Buckland and Conybeare reported the bone bed at Aust Cliff, already known as a source of teeth and bones of fishes and marine reptiles, all preserved shiny black, and concentrated in particular layers that mark a change from terrestrial to marine conditions.

Student Sam Cross, lead author of the paper, said: “It was amazing to be able to work on this classic site. We had visited it on a first-year field trip, and knew it was one of the top ten geological sites in Britain. Then we discovered that so much was unknown about the fossils.”

Over the years, many reports have been made about the larger fossils from the Aust bone bed, including vertebrae, ribs and jaw bones of ichthyosaurs, the dolphin-like marine reptiles of the time.

In addition, larger fish teeth had been noted. But nobody had documented the full range of the specimens, especially the smaller fossils.

Helped by technician Adam Parker from the University’s School of Earth Sciences , the students processed bone bed samples through acid and sieving to extract the tiny teeth and bones.

He said: “These are classic preparation methods. You take great blocks of the bonebed and reduce it by a process of mild acid treatment, washing and concentrating to make the job of picking out the fossils quicker.”

The students identified six species of sharks and four species of bony fishes, as well as other unidentified scales, bones, and coprolites.

Nikola Ivanovski, another of the student team, added: “Coprolites are fossil poops. You can work out who made the poop by their size, and then explore the fossilized contents. Some were full of fish scales and teeth, which showed links in the food chain.”

The food chain shows plankton, shrimps, and shellfish at the bottom, with an array of fishes feeding on these. Then, larger fish fed on the smaller ones, and at the top were the ichthyosaurs and plesiosaurs, long-necked marine reptiles.

Professor Mike Benton , who supervised the project, said: “The bone bed was formed when sea levels rose suddenly about 205 million years ago. In fact, you can trace some of these bone beds widely over southern and central England, and even across to the continent where the same marine transgression is seen in France and Germany.”

The project is one of a series of successful studies conducted by undergraduate students at the University of Bristol.

Claudia Hildebrandt, Curator - School of Earth Sciences, said: “We love to give students this opportunity to try out the reality of research.

“They are awed at first to think they can do something new, but then they have to learn the discipline of hours of hard work and writing and illustrating skills. This is the fourteenth publication in the series.”