The discovery comes after 25 years of preparation to analyse a fossil found in Wyoming and has forced a rethink among researchers on the scientific consensus

An ancient sea monster that once patrolled the seas has been discovered, with analysis of a fossil found 25 years ago revealing it was more than 23 foot in length.

The giant reptile existed 70 million years ago alongside dinosaurs, and scientists say it had a long snake-like neck and crocodile jaws.

It has been named as a Serpentisuchops - which translates as "snakey crocodile face".

Research lead Professor Scott Persons, from the College of Charleston in South Carolina, said: "For comparison, your own neck has a mere seven vertebrae, the Serpentisuchops has 32."

The sea creature is a member of an extinct group of marine reptiles called the plesiosaurs, of which 100 different species have been discovered including a creature that would have weighed 45 tonnes and been 50 feet in length which was discovered on a Norwegian archipelago in 2009.

Persons says this latest discovery is a game changer.

"When I was a student I was taught that all late-evolving plesiosaurs fall into one of two anatomical categories. Those with really long necks and tiny heads, and those with short necks and really long jaws. Well, our new animal totally confounds those categories," he said.

The fossil was discovered a quarter of a century ago in Wyoming, but work on its analysis has only just started as it took many years to carefully and clean and prepare it to be examined.

The researchers say the Serpentisuchops feasted on a diet of small, quick-swimming prey, like squid and small fish.

"The tall, conical teeth are smooth and not serrated with a cutting edge, so this animal wouldn't have been able to bite through thick bone," Persons said.

During the time the creature lived, the American continent was immersed in a shallow sea called the Western Interior Seaway which is where it is thought the animal lived.

Persons told Newsweek : "Serpentisuchops might have gone extinct, due in part to the reduction in the Western Interior Seaway, which occurred 70 million years ago."

However, the discovery is likely just the tip of the iceberg.

"Plesiosaurs were globally distributed... and around for such a long period of time. I suspect that we know only a tiny, tiny fraction of all the plesiosaur species that ever were."