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‘Fake fin’ discovery reveals new ichthyosaur species

A former University of Reading student's dissertation work has helped officially classify a marine reptile from the Jurassic period as a new species.

Rashmi Mistry studied a fossilised baby Protoichthyosaurus held in the University's Cole Museum of Zoology. First discovered in the 1970s, it was initially dismissed as a similar, more common creature, but has now been re-examined and found to be a new species in its own right.

The Biological Sciences undergraduate (now graduated) studied the creature's unusual forefin before contacting the authors of the study, published this month in the Journal of Vertebrate Paleontology. They confirmed not only that Reading's fossil matched the new sepcies, but that it is the only fossilised baby Protoichthyosaurus in existence.

The detailed study was led by palaeontologists Dean Lomax (The University of Manchester) and Professor Judy Massare (State University of New York). It looked at the discovery in 1979 of a new type of ichthyosaur called Protoichthyosaurus by palaeontologist Dr Robert Appleby, who named two species: P. prostaxalis and P. prosostealis. Other scientists, however, dismissed the discovery of Protoichthyosaurus and suggested that it was identical with Ichthyosaurus, a very common UK ichthyosaur.

Discovery

Mr Lomax and Professor Massare found major differences in the number of bones in the front fin, or forefin, of both species. This fundamental difference probably reflects the way both species used them to manoeuvre whilst swimming. Differences were also found in the skulls. But it was another discovery about the fins that also got the team’s attention.

Mr Lomax said: “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.

"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.”

"It had an unusual forefin that matched Protoichthyosaurus, which I understood to be a widely unrecognised genus" - Rashmi Mistry, former University of Reading student

Mr Lomax and Professor Massare then teamed up with former undergraduate student Ms Mistry (University of Reading), who had been studying an unusual ichthyosaur in the collections of the Cole Museum of Zoology, University of Reading, for her undergraduate dissertation.

She said: “Whilst doing my dissertation in 2016, I studied several ichthyosaurs 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."

Lost specimen

More than 20 specimens of Protoichthyosaurus were identified as part of this study. This is significant as each specimen (with a forefin) has the same structure. The specimens are from the Jurassic Period, between 200 – 190 million years old, and come from Somerset, Dorset, Leicestershire, Warwickshire, Nottinghamshire, England, and Glamorgan, Wales.

Whilst searching through collections, Dean also came across a skeleton at The University of Nottingham. This specimen is different to all other known examples of Protoichthyosaurus in the skull and humerus and it has been identified as a new species, which the team have called Protoichthyosaurusapplebyi, in honour of Robert Appleby. It is currently on display as part of the ‘Dinosaurs of China’ exhibition at Lakeside Arts, University of Nottingham.

Full reference:

Lomax, D. R., Massare, J. A. and Mistry, R. (2017). 'The taxonomic utility of forefin morphology in Lower Jurassic ichthyosaurs: Protoichthyosaurus and Ichthyosaurus.' Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1361433