Giant plankton-eating fossil fish discovered in Kansas solves an old mystery
02/18/2010

Giant plankton-eating fishes swam the prehistoric seas for over 100 million years before they became extinct about the same time as the dinosaurs, new fossil evidence has shown. Discoveries by Fort Hays State University alumni and associates of the Sternberg Museum of Natural History played key roles in the discovery.

An international team describes new fossils from Kansas, Europe and Asia that reveal a previously unknown dynasty of giant plankton-eating bony fishes that lived in the oceans of the Earth during the Age of Dinosaurs, between 66 million and 172 million years ago. Paleontologists from Fort Hays State University, the United Kingdom’s Oxford University, Chicago’s DePaul University, the University of Kansas, the University of Glasgow and the Rocky Mountain Dinosaur Research Center in Colorado report their findings in this week’s Science, the peer-reviewed journal of the American Association for the Advancement of Science.

“Giant plankton-feeders in our modern oceans -- baleen whales, basking sharks and manta rays -- include some of the largest living animals," said Mike Everhart, adjunct curator of paleontology at FHSU's Sternberg Museum of Natural History and an author of the report.

"The fact that such creatures appeared to be missing from the fossil record for hundreds of millions of years has been an ongoing mystery among marine paleontologists," he said. "We had to conclude that there were no big filter feeders in the oceans during the Age of Dinosaurs, but our recent discoveries now reveal that a diverse group of giant fishes occupied this ecological role in these prehistoric oceans for more than 100 million years."

Several of the most important discoveries have come from Smoky Hill Chalk of western Kansas. FHSU alumni and Sternberg Museum personnel have figured in two of the most important, including the most complete specimen, which was collected in 2009 by Everhart and which is now in the collections of the Sternberg Museum. Other remains have come from around the world, including Dorset and Kent in the United Kingdom, and Japan. Some members of this filter-feeding fish group are estimated to have been up to 30 feet long, similar in size to modern plankton-eating giants such as the basking shark.

"One of the reasons these big fishes were overlooked or misidentified lies in their anatomy," said Dr. Matt Friedman, a lecturer in palaeobiology at Oxford. "Over their evolutionary history, these fishes reduced the amount of bone in their skeletons, probably to save weight, with the consequence that most of their hard parts were easily scattered after death. As it turns out, the only parts you routinely find in the fossil record are their well-developed fore fins."

With few clues to go on, early paleontologists concluded that these isolated fins were from something like a modern-day swordfish. This changed recently when the bones of the skull were discovered preserved along with the fins in a specimen from the University of Kansas.

"Instead of finding a head with a long sword-like snout and jaws lined with predatory fangs," said Friedman, "they found something completely different: long, toothless jaws supporting a gaping mouth, and long, rod-like bones that contributed to the huge gill arches needed to filter out enormous quantities of tiny plankton." The team named this KU fish Bonnerichthys gladius, honoring the Kansas Bonner family who collected the fossil in 1971. It was discovered by Chuck Bonner, who graduated FHSU with bachelor's (1972) and master's (1974) degrees in art.

Remains of similar giant plankton-eating fishes were known from much older rocks in England and Europe, but they were thought to be a short-lived and unsuccessful evolutionary experiment. "I started examining museum collections and found more examples that had been overlooked or misidentified," said Friedman. Revisiting previously collected fossils netted the team evidence that these fishes thrived for millions of years and colonized many parts of the globe.

Another, even more complete specimen was discovered in 2008 by Dr. Kenshu Shimada, an associate professor in the Environmental Science Program and the Department of Biological Sciences at DePaul University, Chicago, while on a field trip with Everhart. Shimada earned bachelor's (1993) and master's (1994) degrees in geology from FHSU and is also a research associate at the Sternberg Museum. Everhart returned to collect the specimen in 2009, and although it is still being prepared, it appears to be most of a complete fish, from the front of the skull to the end of the tail.

"We now have the best specimen in the world at the Sternberg," said Everhart.

"The odds of the discovery were extremely low given that less than 20 specimens of this species, mostly fragments, have been found in the last 150 years of extensive fossil-collecting history in that region," said Shimada. The specimen added new data to the publication and will be described in detail in a follow-up study.

It is interesting to note, said Everhart, founder of the Web site "Oceans of Kansas," that the ancestors of large modern filter-feeders such as baleen whales and whale sharks only appeared after the extinction of Bonnerichthys and its relatives, suggesting that today’s filter-feeders evolved to fill the ecological vacancy left by the extinction of these plankton-eating contemporaries of the dinosaurs.

For more information, contact Everhart at (316) 788-1354 or by e-mail at meverhar@fhsu.edu.


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