An astonishing fossil of an extinct 'sea dragon' discovered by a wetland conservationist one day at work has been hailed as the largest and most complete fossil of its kind ever found in Britain.

The fossil, identified as an ichthyosaur, an ancient marine reptile that swam in Earth's prehistoric oceans when dinosaurs walked on land, was found poking out of the mud, and scientists say the ancient specimen is practically complete from tip to tail.

"Our specimen, the Rutland Ichthyosaur or the Rutland Sea Dragon, is the biggest complete ichthyosaur ever found in Britain in over 200 years of collecting these things scientifically," says paleontologist Dean Lomax who led the excavation.

The fossilized ichthyosaur. (Anglian Water)

Joe Davis, a conservationist with the Leicestershire and Rutland Wildlife Trust, first spied an exposed jawbone of the fossil in February 2021 during routine landscaping works at the Rutland Water Nature Reserve, a small wetland conservation area in the English Midlands.

The fossilized remains were excavated over three weeks in a delicate operation involving plenty of plaster and wooden splints used to protect the gigantic yet fragile specimen as it was removed from its muddy tomb.

Faced with mounting bird poop and awful weather, the team of paleontologists, conservationists, and volunteers ultimately prevailed, safely uncovering and extracting the 10-meter-long fossil and its entire backbone consisting of more than 150 individual vertebrae.

"I know lots of people have spent their lives looking for something like this and I've been very lucky to come across it," Davis told New Scientist about the find, which was initially dismissed by his colleague, Paul Trevor, as "just a pipe".

Ichthyosaurs, which range in size from 1 meter (3.3 feet) to more than 25 meters (85 feet) and resemble modern-day dolphins, first appeared roughly 250 million years ago and died out about 160 million years later.

The Rutland Sea Dragon lay covered in clay-rich rocks that the researchers say were deposited during the early Jurassic period, around 180 million years ago. It is most likely a species called Temnodontosaurus trigonodon, although the preliminary findings have not yet been peer-reviewed.

"It is a truly unprecedented discovery and one of the greatest finds in British paleontological history," says Lomax, a visiting scientist at the University of Manchester.

Two smaller, partial ichthyosaur skeletons were found decades ago in the same wetland area, so finding another was not totally unexpected for local scientists, but the size of the new fossil – which dwarfs its discoverers – was still a "total surprise".

"We thought that the specimen might have had its tail destroyed or scattered by bulldozers when the lagoon had been dug out some 10 years previously," writes paleontologist Nigel Larkin in a blog post about the find.

"We soon uncovered ribs, a portion of the skull, and – amazingly – revealed an entire vertebral column down to the very tip of the tail where the vertebrae are the size of a penny."

Uncovering the skeleton was just the first step, and extracting the giant fossil was a serious task: Once encased in plaster, the skull alone weighed just under 1 tonne.

"It's not often you are responsible for safely lifting a very important but very fragile fossil weighing that much," says Larkin, a specialist paleontological conservator.

The spectacular specimen, only recently revealed to the public, is still wrapped in its plaster cast, stored in a secret location, and has not yet been studied in detail. The researchers plan to prepare academic papers describing the discovery once it has been cleaned up and conserved.

"Despite the thousands of ichthyosaurs discovered in Britain, none of them are quite as large as this specimen, and few examples of this genus [have] been found in the UK that are this complete," Larkin added in a blog post.

Luckily for fossil fiends, the team took a 3D scan of the fully exposed specimen (which you can view in jaw-dropping detail here) before any bones were removed.

The researchers also took samples of fossils surrounding the main specimen, including squid-like ammonites and belemnites, to better understand the environment where the ichthyosaur lived and died, and to date the animal to roughly 182 million years old.

"If our identification of the ichthyosaur is correct, as a species called Temnodontosaurus trigonodon, this will provide new details on the geographic range of the species, as it hasn't been confirmed from the UK before," says paleontologist Mark Evans of the University of Leicester.

Most other Temnodontosaurus fossils, known for their incredibly large eyes, have been found in Germany and North America, with another in Chile.

The team plans to apply for funding for the next phase of conservation to clean and prepare the fossil, after which they hope the creature's skeleton will be placed on permanent display close to where it was found.