The Big Fish that Ate Small

Thursday, February 18, 2010

Fish

Giant plankton-eating fishes roamed the prehistoric seas, including those over the land now known as Kansas, for more than 100 million years before they were wiped out in the same event that killed off the dinosaurs, new research shows.

 An international team that includes researchers from the University of Kansas describe how new fossils from Asia, Europe and the United States reveal a previously unknown dynasty of giant bony fishes that filled the seas of the Jurassic and Cretaceous periods, between 66 million and 172 million years ago. The team reported their findings in the Feb. 19 edition of the journal Science.

Several of the most important new fossils came from the famous chalk deposits of western Kansas, with other remains from as far afield as Japan and from Dorset and Kent in the United Kingdom. Some members of this filter-feeding fish group are estimated to have been up to 30 feet long, a similar size to modern plankton-eating giants such as the basking shark. Revisiting previously collected fossils netted evidence that these fishes thrived for millions of years and colonized many parts of the globe.

The research team included Larry Martin, curator of vertebrate paleontology at the KU Biodiversity Institute, and researchers from Oxford University, DePaul University, Fort Hays State University, the University of Glasgow, Triebold Paleontology Inc. and the Rocky Mountain Dinosaur Research Centre.

Matt Friedman, lead author of the research and a lecturer at Oxford, said that because modern giant plankton feeders — such as baleen whales, basking sharks and manta rays — include the largest living vertebrate animals, scientists had long wondered why such animals were missing from the fossil record for hundreds of millions of years.

“We used to think that the seas were free of big filter feeders during the age of dinosaurs, but our discoveries reveal that a dynasty of giant fishes filled this ecological role in the ancient oceans for more than 100 million years,” Friedman said.

The big fishes were overlooked or misidentified because over time, the amount of bone in their skeletons diminished, probably to save weight. The only parts routinely found in the fossil record are their well-developed forefins. Martin said that this changed when the KU Biodiversity Institute acquired a more complete skeleton that revealed the unusual features of the giant fish’s head.

“Instead of finding a head with a long sword-like snout and jaws lined with predatory fangs, 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,” Friedman said.

The team named the fish Bonnerichthys, after the Marion Bonner family. The Bonners are a Kansas family of fossil collectors who discovered the fossil fish as well as many other important specimens now housed at KU and the Sternberg Museum in Hays. The research was titled “100-Million-Year Dynasty of Giant Planktivorous Bony Fishes in the Mesozoic Seas.”

News Type: 
Research News