The main difference between the two animals’ fins is subtle for the untrained eyes: they had a different amount of bones. For the animals, it could’ve led to specific ways of maneuvering with their fins, causing them to take different niches or lifestyles. This suggests that the two ichthyosaurs, which shared the Early Jurassic oceans 200-190 million years ago, were much like how a house cat is different from a puma.
What complicates this further is that some Ichthyosaurus specimens had pathological conditions where some of their bones co-ossified, or fused together, making them resemble Protoichthyosaurus. In their study, Lomax and Massare “had to rigorously look at all of their forefins,” including specimens with mixed-up body parts. “When it wasn't a 'fake', we found the co-ossifications,” Lomax stated, referring to the subtle line that marks where the bones fused together.
Adding to this study was Rashmi Minstry, former undergraduate student from University of Reading. While working on her dissertation in 2016, she discovered a juvenile fossil with a fin feature that matched Protoichthyosaurus specimens Lomax was studying in the university’s collections. This specimen is the only known juvenile from this genus to date.
In the collections of The University of Nottingham, Lomax also discovered a single specimen of Protoichthyosaurus unlike the other 20 specimens he studied. Its skull has a notably rounder base which tapers more drastically to its slender snout. As a part of the same study, Lomax and Massare named this fossil Protoichthyosaurus applebyi to honor of Dr. Robert Appleby, who gave the first species the name Protoichthyosaurus prostaxalis in 1979.
Protoichthyosaurus and Ichtyosaurus are part of a lineage of marine reptiles collectively called ichthyosaurs. They swam the seas of the Early Triassic to Late Cretaceous, roughly 248 to 90 million years ago. Although they lived all over the globe, many discoveries of ichthyosaurs happened in and around England where Lomax is based.
Through this study, Lomax and Massare have once again shown that combing through old specimens is just as important as digging up new ones. By applying the latest knowledge and technological innovations, even last century’s bones can tell us new stories.
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
University of Nottingham - Dean R. Lomax