Scientists have lately discovered two plankton-munching fossil fish species of the Rhinconichthys genus from the cretaceous period, swimming the oceans around 92 million years ago when dinosaurs still roamed Earth.

Rhinconichthys are outstandingly rare large-mouthed fish, previously known by a single species from England. But that count has been expanded to two more and from other geographical locations, thanks to a new skull discovered in Colorado in the United States (named R. purgatoirensis) and a reexamined skull from Japan (R. uyenoi).

Study author and paleobiologist Kenshu Shimada of DePaul University was part of the team that named the genus back in 2010. "[B]ut we had no idea back then that the genus was so diverse and so globally distributed," he said in a press release.

This interesting genus belongs to a now-extinct group of bony fish known as pachycormids, which boasts of the largest bony fish ever to have existed on the planet.

The more than 6.5-feet-long Rhinconichthys feasted on plankton using its oar-shaped mouth.

The feeding process is a unique one: a pair of bones called hyomandibulae formed a huge lever to protrude and swing the animals' jaws open like a parachute, extra wide to receive as much plankton-laced water into the mouth. Think of the way sharks open their mouth to attack their food.

Suspension-feeding or a plankton-rich diet during the dinosaur age is an emerging area of interest. It is, however, common today among certain marine vertebrates, such as the whale shark and blue whale.

Rhinconichthys is named from a whale shark called Rhincodon.

Three different Rhinconichthys from three separate geographical regions now turn up in scientific literature, each represented by a single skull. To Shimada, it isn't any less mind-boggling.

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

The findings appeared on the journal Cretaceous Research.

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