A team of researchers found two new fish species – from the Cretaceous Period – related to Rhinconichthys, which were once thought to have only lived in England.
The fossils likely belong to the Rhinconichthys genus that inhabited the oceans about ninety-two million years ago. Rhinconichthys are bony fish with large mouths; before the new discovery, experts only knew of Rhinconichthys taylori, an extinct species of bony fish that lived in what is modern-day England. Researchers found the skulls of the two new species in Colorado – R. purgatoirensis – and in Japan – R. uyenoi.
Kenshu Shimada, author of the study and a paleobiologist at DePaul University, said that when he and his colleagues named Rhinconichthys in 2010, they only knew of one species from England. At the time, the researchers had no clue that the genus was globally distributed and so diverse, Shimada noted.
There are now three different species of Rhinconichthys from three separate corners of the world, according to Shimada. For each of the species only one skull was found.
R. purgatoirensis and R. uyenoi, as well as the species form England, belong to the broader group of prehistoric fish called pachycormids – an extinct family of ray-finned fish. An analysis of the fossils will help scientists better understand the feeding mechanisms of these prehistoric fishes that are known to have fed only on plankton.
The fish were probably more than six feet (1.82 m) long, Professor Shimada said. It would be quite difficult for a fish the size of R. purgatoirensis and R. uyenoi to feed only on plankton, which means that the fish must have required some type of unusual adaptation, he explained. Judging by the hyomandibulae (pair of bones) found in the skull, the fishes likely had the ability to open their mouths very wide to maximize the amount of plankton they ate with a single ‘bite’.
Bruce Schumacher from the United States Forest Service was the one who discovered the new species. Apart from Schumacher and Shimada, the research team also included Anthony Maltese, curator at the Rocky Mountain Dinosaur Resource Center (RMDRC), and Jeff Liston, an associate professor at Yunnan Key Laboratory for Palaeobiology and former research associate at National Museums of Scotland.
The findings will be published the international scientific journal Cretaceous Research.
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