Fossils of “Big Mouth” Fish from Cretaceous Period Uncovered

An international team of scientists have uncovered two new species of plankton-eating, big-mouthed, bony fish from the Cretaceous Period, about 92 million years ago when dinosaurs roamed the Earth.

The two new species, part of the genus Rhinconichthys, have been named Rhinconichthys purgatoirensis and Rhinconichthys uyenoi. The genus belongs to the extinct bony fish group called pachycormids, which before this study, had only one known fossil example – one found in England that was part of the first-ever Rhinconichthys discovery in 2010.


An artist depiction of the genus Rhinconichthys, which lived some 92 million years ago during the Cretaceous Period. Image credit: Robert Nicholls

The findings are based on a new fossil find in Colorado, which would eventually turn out to be R. purgatoirensis, and a newly identified fossil in Japan, which was R. uyenoi.

“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 author of the study Kenshu Shimada at DePaul University.

According to researchers, Rhinconichthys were more than 6.5 feet in length and fed exclusively on plankton. They evolved a unique ability to protrude and swing their jaws open extra wide to capture more plankton-rich material, much like modern day sharks can do.

Marine biologists call the process of eating plankton suspension-feeding. This behaviour is known among some species today, including the Blue Whale, Manta Ray and Whale Shark, but remains a new emerging area of research in the dinosaur era.

“Based on our new study, we now have three different species of Rhinconichthys from three separate regions of the globe,” 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 set to be published in the journal Cretaceous Research.

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