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Two Cretaceous plankton-eating fish species were discovered recently thanks to the efforts of an international research team.
The two plankton-eating fish species belong to the genus Rhinconichthys. During the Cretaceous, these strange fish would feed on the plankton of the Cretaceous oceans. The intriguing plankton-eating fish are little known to scientists. The few fossils discovered until now couldn’t reveal too much information on the species belonging to the genus Rhinconichthys.
One previously discovered fossil came from England. Now, according to Kenshu Shimada with DePaul University, a new Colorado fossil has brought an extended knowledge of the plankton-eating fish species that lived 92 million years ago. The plankton-eating fish fossil from England, along with that from Colorado were studied in relation with a third fossil found in Japan.
Thanks to the higher number of fossils and their well-preserved state, two Cretaceous plankton-eating fish species were discovered.
According to Kenshu Shimada, the two new species are called R. Purgatoirensis and R. uyenoi. At the time the genus Rhinconichthys was named in 2010, only one fossil had been discovered. Shimada declared that:
“We had no idea back then that the genus was so diverse and so globally distributed”.
With one fossil in England, one is Japan and another in Colorado, it stands clear that these relatively large fish species covered a wide geographical area. What sets these Cretaceous plankton-eating fish apart from others is their feeding pattern.
Scientifically named specialized suspension-feeding, this way of gorging down food implied that the plankton-eating fish species had a peculiar anatomical structure. The study authored by Bruce A. Schumacher with the United States Forest Service, Jeff Liston with the National Museum of Scotland and Anthony Maltese with the Rocky Mountain Dinosaur Resource Center will be published in the Cretaceous Research journal.
The species in the Rhinconichthys genus belong to a larger group known as the pachycormids. This group harbors some of the largest bony fish that have ever existed on this planet. Now extinct, these large bony fish would have been feeding exclusively on plankton. Rhinconichthys genus fish species are estimated to have grown to over 6.5 feet in length.
The distinctive feature of the large bony fish is the pair of bones dubbed the hyomandibulae. These bones would have come together to form an oar-like lever. The oar-like lever would have swung the jaw of the fish wide open during the specialized suspension-feeding process. The gaping opening would take in as much plankton as possible to keep the two plankton-eating fish species well-fed for a while.
Similar feeding patterns as that of two plankton-eating fish species are known today with the Blue Whale, the whale shark or the manta ray.