Ancient, Massively Big-Mouthed Fish Once Roamed the Oceans of the Cretaceous

Two massively big-mouthed fish once roamed the oceans of the Cretaceous period. Scientists have found two new plankton-eating fossil fish with giant mouths that lived 92 million years ago.

"I was in a team that named Rhinconichthys in 2010, which was based on a single species from England, but we had no idea back then that the genus was so diverse and so globally distributed," said Kenshu Shimada, one of the researchers, in a news release.

Rhinconichthys belongs to an extinct bony fish group called pachycormids, which contains the largest bony fish ever to have lived. In this latest study, the researchers focused on highly elusive forms of this fish group that actually ate plankton.

Rhinconichthys was estimated to be more than 6.5 feet and fed on plankton. One pair of its 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. This is similar to the way many sharks open their mouths.

A planktivorous diet, also called suspension-feeding, is known among some specialized aquatic vertebrates today, such as the blue whale and the manta ray.

"Based on our new study, we now have three different species of Rhinconichthys from three different species of Rhinconichthys from three separate regions of the globe, each represented by a single skull," said Shimada. "This tells just how little we still know about the biodiversity of organisms through Earth's history. It's really mindboggling."

The findings are published in the journal Cretaceous Research.

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