Scientists discover fossils of two new giant-mouthed fish species

Scientists have discovered two new plankton-eating fossil fish species which could swing the jaws open extra wide, like a parachute, and swam the oceans 92 million years ago, when dinosaurs roamed the planet.

These fossil fish of the genus called Rhinconichthys are exceptionally rare, known previously by only one species from England, researchers said. But a new skull from North America, discovered in Colorado along with the re-examination of another skull from Japan have tripled the number of species in the genus with a greatly expanded geographical range, they said. "These species have been named R purgatoirensis and Ruyenoi, respectively," said Kenshu Shimada from DePaul University in US.

Rhinconichthys belongs to an extinct bony fish group called pachycormids, which contains the largest bony fish ever to have lived. The new study specifically focuses on highly elusive forms of this fish group that ate plankton. Rhinconichthys was estimated to be more than 6.5 feet, and had a highly unusual specialisation for bony fish.

One pair of bones called hyomandibulae formed a massive oar-shaped lever to protrude and swing the jaws open extra wide, like a parachute, in order to receive more plankton-rich water into its mouth, similar to the way many sharks open their mouth, researchers said.

A planktivorous diet, also called suspension-feeding, is known among some specialised aquatic vertebrates, including the Blue Whale, Manta Ray and Whale Shark. "Based on our new study, we now have three different species of Rhinconichthys from three separate regions of the globe, each represented by a single skull," said Shimada.

The findings were published in the journal Cretaceous Research.