A new species of ichthyosaur has been identified, after fossils were re-examined by palaeontologists more than 35 years after they were dismissed as belonging to a more common species.

Ichthyosaurs are large marine reptiles that first appeared around 250 million years ago, before dying out 160 million years later.

In 1979, palaeontologist Robert Appleby announced a new type of ichthyosaur called Protoichthyosaurus after inspecting several specimens from the UK. However, other researchers rejected the discovery, saying the bones were identical to Ichthyosaurus, which are commonly found across the region. Thus, the fossil was consigned to museum storerooms.

Now a new study, led by Dean Lomax from the University of Manchester and Professor Judy Massare from State University of New York, has re-examined and compared Protoichtyosaurus and Ichthyosaurus, finding major differences in the number of bones in the front fin of both species. Variations in the skulls were also found.

But it was another discovery regarding the fins that surprised the team.

"This unusual forefin structure was originally identified by Robert Appleby in 1979, but some of the historic specimens he examined had been 'faked', and this fakery had been missed until now," Lomax explains.

"In some instances, an isolated fin of an Ichthyosaurus had been added to a Protoichthyosaurus skeleton to make it appear more complete, which led to the genuine differences being missed. This has been a major problem because it stopped science from progressing. We also found some pathological fins, including Ichthyosaurus fins with pathologies that mimic the Protoichthyosaurus forefin structure".

Lomax and Massare were aided by Rashmi Mistry, a former undergraduate student from the University of Reading who had been studying an unusual Ichthyosaurus from the Cole Museum of Zoology for her dissertation.

"Whilst doing my dissertation in 2016, I studied several Ichthyosauruses in the collections, including a very small skeleton. It had an unusual forefin that matched Protoichthyosaurus, which I understood to be a widely unrecognised genus. However, when I contacted Dean, he was very excited. He told me that this little skeleton is the only known small juvenile Protoichthyosaurus," added Rashmi.

During the study, more than 20 specimens of Protoichthyosaurus were identified, all originating from the Jurassic Period and ranging from 200 to 190 million years old. They were discovered in many places around the UK, including Somerset, Dorset, Leicestershire, Warwickshire, Nottinghamshire and Glamorgan.

In addition, Lomax came across a Protoichthyosaurus specimen at the University of Nottingham with variations in the skull and humerus. This has now been identified as another new subspecies that the team has named Protoichthyosaurus applebyi in honour of the late palaeontologist Robert Appleby.