Rescuing a 199-million-year-old ammonite graveyard

The rock bed at Lyme Regis in Dorset is home to many ammonites, an extinct group of marine molluscs.

There are so many that the rocks have earned the name 'ammonite pavement'. They record a time 199 million years ago when marine ecosystems were returning to normal after the Late Triassic mass extinction.

The fossil bed is the only one of its kind in the world - nowhere else features so many big ammonites, which are up to 70 centimetres in diameter.

The bed is part of the Jurassic Coast World Heritage Site, protected as a Site of Special Scientific Interest and National Nature Reserve.

Last winter, storms broke up a large part of the ammonite pavement - measuring nine metres by six metres - exposed on Monmouth Beach. A number of blocks broke off, and some overturned.

Natural England, which looks after the site, asked the Museum to help preserve the blocks for future generations. The Museum has acquired four large slabs and several smaller ones for display and research.

Dr Jon Todd, Senior Curator of Benthic Molluscs at the Museum, is enthusiastic about the important addition to the collection:

'We have isolated specimens of the ammonites in our collection, but this is a unique opportunity to preserve large blocks that show both fossils and sediment with a wide range of fantastic burrow systems produced by worms and crustaceans, which is scientifically much more valuable,' he says.

Museum palaeontologist Prof Richard Twitchett continues, 'The exciting thing about these blocks is that they show us the animals that lived on and in the sea floor together with those that were swimming in the water above. It's an entire Jurassic ecosystem.'

Fossil rescue

With each square-metre slab weighing around 250 kilogrammes, moving the blocks from the beach was not an easy process.

A team of Museum scientists visited the site to assess the condition of the blocks and plan their safe journey from the beach to London.

'Fortunately, the selected blocks are very robust and the ammonite-bearing surfaces are mostly free from fractures,' says fossil preparator Mark Graham.

On the day of the rescue, curator Zoë Hughes worked with a team of volunteers put together by Natural England to carefully manoeuvre the blocks off the beach, protecting them with conservation-grade padding. From there, the blocks were loaded onto a lorry able to cope with heavy loads.

With the slabs now at the Museum, staff have drawn up a plan for their conservation, preparation and for future research and display opportunities.

Graham adds, 'It is great that the Museum continues to take a lead in protecting such objects, which form such an important part of our geological heritage.'

An Early Jurassic sea floor frozen in time

Prof Twitchett has been conducting field research in the Lyme Regis area for more than 10 years. He is looking forward to the new research opportunities opened up by the blocks.

He says, 'The fossils preserve the animals that were living in a shallow-shelf sea not long after a major extinction event associated with rising carbon dioxide levels and global warming. Studying them helps us to understand how such ecosystems respond to environmental change.

'The storm damage has provided us with a unique opportunity to study the entire bed, including the normally hidden underside. These blocks will not only provide unprecedented detail about the changing ecology of the Jurassic sea floor, but may also help answer the conundrum of why there are so many ammonites in this iconic bed.'

The Museum would like to thank the landowner George Allhusen for his generous donation of the slabs to the Museum's collections.