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Prehistoric 'Big-Mouthed' Fish Fossil From Cretaceous Period Discovered

First Posted: Feb 09, 2016 01:21 PM EST

Scientists have discovered two usual "big-mouthed" fish fossils from the Cretaceous Period, about 92 million years ago. The team of international researchers found that the ancient fish belonged to a plankton-eating species of fish known as "Rhinconichthys," which swamed the Cretaceous ocean during the same period when the dinosaurs roamed the land masses, according to a study.

The team noted that "Rhinconichthys" is quite rare and only one species has been identified in England. However, a new skull discovered in Colorado along with another from Japan have tripled species' genus in an extensive geographical range. These species have been named "R. purgatoirensis" and "R. uyenoi," according to the researchers.

"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," Kenshu Shimada, coauthor of the study, said in a news release.

"Rhinconichthys" belonged to an extinct bony fish group known as pachycormids, which are the largest bony fish that has lived. Pachycormids grew almost over 6.5 feet and their diet consisted of plankton. Pachycormids contained a pair of bones known as hyomandibulae, which created a large oar-shaped lever enabled the fish's jaw to open extremely wide similar to a parachute. This method allowed the fish to obtain additional plankton-rich water into its mouth.

Pachycormids had a planktivorous diet, also referred to as suspension-feeding, which is common among some modern marine creatures such as whale sharks, blue whales and manta ray.

"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," Shimada said. "This tells just how little we still know about the biodiversity of organisms through the Earth's history. It's really mindboggling."

The findings of this study were published in Cretaceous Research.

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