Huge ancestors of squid up to 1.8 metres wide once littered the sea floor in what is now East Sussex before being wiped out by a meteor, according to new research.
Giant ammonites once thrived on both sides of the Atlantic – in southern England and Mexico – before suffering the same fate as the dinosaurs.
An international team of scientists has been investigating why so many of the cephalopods have been found in one corner of Sussex.
Among them is Professor Andy Gale, from the University of Portsmouth, who said: “This giant species is commonly found in the chalk on the foreshore at Peacehaven in East Sussex, where erosion by the sea has exposed moulds of the shells.
“The largest specimens are females, which probably spawned once and subsequently died.
“The chambered shells were buoyant, and floated in the chalk sea for a long time before finally sinking to the bottom, where they have been preserved for millions of years.”
The team studied 154 giant ammonites from the Cretaceous period found in rocks in Germany, Mexico and the UK.
Professor Gale said: “These enormous, long-extinct, shelled cephalopods, related to squid and octopus, achieved a maximum shell diameter of 1.8 metres and are best known from a specimen in a German museum.”
Giant ammonites – relatives of the modern-day squid and octopus – were wiped out by the same end-Cretaceous meteorite impact 66 million years ago that ended the reign of the dinosaurs.
Professor Gale said although fossil finds of the species are extremely rare and little is known about them, the concentration of them in Sussex means scientists can start piecing together the story of their evolution.
Before they were properly understood, the spiral-shaped fossils of ammonites led people to believe they were actually coiled-up snakes that had been turned to stone, earning them the nickname “snakestones”.
The subclass Ammonoidea, a group that is often referred to as ammonites, first appeared about 450 million years ago.