0328 GMT February 18, 2020
The ‘sea dragon’ belongs to a group that swam the world's oceans 200 million years ago, while dinosaurs walked the land, according to bbc.com.
The specimen is the largest Ichthyosaurus to be described, at more than three meters long.
It was discovered on the coast of England more than 20 years ago, but has remained unstudied until now.
Paleontologist Sven Sachs saw the fossil on display at a museum in Hannover. He contacted UK paleontologist, Dean Lomax, who is an expert on Ichthyosaurs.
The University of Manchester paleontologist said, ''It amazes me that specimens such as this [the biggest] can still be 'rediscovered' in museum collections.
''You don't necessarily have to go out in the field to make a new discovery.''
The reptile belongs to the species, Ichthyosaurus somersetensis, which is named after the county in south west England where many ancient marine reptile specimens have been unearthed.
It was dug up at Doniford Bay, Somerset, in the 1990s and eventually found its way into the collections of the Lower Saxony State Museum in Hannover.
The reptile was an adult female that was pregnant at the time of death.
Dean Lomax added, ''This specimen provides new insights into the size range of the species, but also records only the third example of an Ichthyosaurus known with an embryo. That's special.''
During the age of the dinosaurs, the ocean was home to many types of ichthyosaur or ‘sea dragon’.
They appeared in the Triassic, reached their peak in the Jurassic, then disappeared in the Cretaceous — several million years before the last dinosaurs died out.
Ichthyosaurs were among the first skeletons to be discovered by early fossil-hunters, at a time when theories of evolution and concepts of geology were in their infancy.
The famous fossil hunter Mary Anning discovered the first complete fossil of an ichthyosaur in the cliffs near Lyme Regis, Dorset, in 1810.
Her discovery shook up the scientific world and provided evidence for new ideas about the history of the Earth.
The study was published in the journal, Acta Palaeontologica Polonica.