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Officials last week revealed that the U.S. contribution to ITER could cost $3.9 billion by 2034—roughly four times the...
An experimental hepatitis B drug that looked safe in animal trials tragically killed five of 15 patients in 1993. Now,...
Using the two high-quality genomes that exist for Neandertals and Denisovans, researchers find clues to gene activity...
A new report from the Intergovernmental Panel on Climate Change (IPCC) concludes that humanity has done little to slow...
Astronomers have discovered an Earth-sized planet in the habitable zone of a red dwarf—a star cooler than the sun—500...
Three years ago, Jennifer Francis of Rutgers University proposed that a warming Arctic was altering the behavior of the...
- 17 April 2014 12:48 pm , Vol. 344 , #6181
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Nothing to Bite On
4 January 2002 (All day)
Lampreys and other living relatives of primitive vertebrates don't have jaws. But that doesn't mean they're mild-mannered vegetarians; some attack their prey of fish with the fury of a wolverine. Equally nasty were the eel-shaped conodonts, an extinct jawless fish. These and other observations have led some researchers to propose that jaws evolved in response to increasingly aggressive hunting habits by jawless ancestors. But a new study takes a bite out of this widespread idea.
Mark Purnell of the University of Leicester, United Kingdom, tested the notion by looking at the heterostracans, a group of extinct jawless fishes that were a dominant slice of vertebrate life for 140 million years until they went extinct at the end of the Devonian. They were relatives of the conodonts, and they shared a more recent common ancestor with the first jawed fish. Some researchers argue that the heterostracans were predators.
In the 7 January issue of the Proceedings of the Royal Society, however, Purnell argues that they were better suited for filter feeding. Using an electron microscope, Purnell took a close look at the oral plates that line the mouth. The plates were not worn on their tips, as one would expect if they had bit into prey. And they were covered with denticles not much more than 100 micrometers long and delicately shaped like triangles and maple leafs. "If this animal tried to grab hold of prey, the denticles would get broken," he says. Moreover, because the denticles pointed toward the front of the mouth, they would have prevented anything other than microscopic food from entering.
Philippe Janvier of the National Natural History Museum in Paris says the study presents "the first good evidence of filter feeding in these early jawless fossil vertebrates."