Museum Plaster Model was Actually the Fossil of a New Ichthyosaur Species

These extinct, dolphin-shaped marine reptiles swam the oceans for millions of years during the Triassic, Jurassic, and Cretaceous. Back in 2008, Dean Lomax from the University of Manchester came upon a plaster copy of an ichthyosaur fossil in the collections of the Doncaster Museum and Art Gallery in the U.K. Except it wasn’t a cast at all: Not only was it real, it was different enough from any known specimen to warrant its own species.

The fossil was found along Dorset's Jurassic Coast in the early 1980s, and it’s unclear how it became mistaken for a copy. But after his realization, Lomax, together with SUNY Brockport’s Judy Massare, examined the fossil over the course of five years. They identified several unusual features of the limb bones (the humerus, forefin, and femur) and the shoulder (or pectoral girdle) that were completely different from any other ichthyosaur known. “That became very exciting,” Dean says in a news release. “After examining perhaps over a thousand specimens we found four others with the same features as the Doncaster fossil.” At least three of them are juveniles. 

The Doncaster fossil—which likely belonged to a subadult animal or older—dates back to between 189 and 182 million years in an early Jurassic period called the lower Pliensbachian. It’s the most complete ichthyosaur of this age. They named it Ichthyosaurus anningae after Mary Anning, who began collecting ichthyosaurs in the early 1800’s. “Mary and her brother, Joseph, discovered the first ichthyosaur specimen to be scientifically recognized, collected at Lyme Regis around 1811,” Dean adds.

Furthermore, the specimen was especially well preserved. "We could see tiny hook-shaped features that were actually the hooks from the tentacles of squid," he tells BBC. "So we know what its last meal was." The duo also suspects that there were differences in the humerus between males and females of this species. In some groups of reptiles (both living and extinct), males and females have different limb bones—something’s that never been applied to ichthyosaurs before.