The new discovery by scientists from the University of Portsmouth is a species of the so-called 'living fossil' coelacanths which still swim in the seas, surviving the extinction that killed off the dinosaurs.
The discovery was purely serendipitous. Professor David Martill, a palaeontologist from the University's School of the Environment, Geography and Geosciences, had been asked to identify a large bone in a private collection in London.
The collector had bought the specimen thinking the bone might have been part of a pterodactyls' skull. Professor Martill was surprised to find it was not in fact a single bone, but composed of many thin bony plates.
He said: "The thin bony plates were arranged like a barrel, but with the staves going round instead of from top to bottom. Only one animal has such a structure and that is the coelacanth - we'd found a bony lung of this remarkable and bizarre looking fish.
"The collector was mightily disappointed he didn't have a pterosaur skull, but my colleagues and I were thrilled as no coelacanth has ever been found in the phosphate deposits of Morocco, and this example was absolutely massive!"
An example of what a complete fish fossil coelacanth looks like. This one is from the Jurassic of German.
The fossil had been embedded in a block of phosphate, backed with plaster and covered in a coating of lacquer, which had caused the bones to turn brown. It was found next to a pterodactyl which proves it lived in the Cretaceous era - 66 million years ago.
The private owner offered to cut the remains of the bony lung off the slab and give it to the team for free. They then had to remove the coating and further expose the bones using specialist equipment, including dental tools and fine brushes.
The original slab, as purchased, with the coelacanth ossified lung in close proximity to a series of associated, but disarticulated wing elements of a large, but indeterminate pterosaur.
He said: "We only had a single, albeit massive lung so our conclusions required some quite complex calculations. It was astonishing to deduce that this particular fish was enormous - quite a bit longer than the length of a stand-up paddleboard and likely the largest coelacanth ever discovered."
Coelacanth fishes first appeared (evolved) 400 million years ago - 200 million years before the first dinosaurs. It had long been believed to be extinct, but in 1938 a living coelacanth was found off South Africa.
The fossil is now being returned to Morocco where it will be added to the collections in the Department of Geology at Hassan II University of Casablanca.
The research is published in Cretaceous Research.
