Aside from mammals, few animals chew. This stingray species is an exception.
There’s a new masticator in town. Scientists have found that at least one species of stingray masticates, or chews, its food before swallowing — an ability that was previously thought to be largely unique to mammals. With high-speed video, they documented freshwater ocellate river stingrays from the Amazon River chomping and grinding their prey in a very human-like way.
The researchers, from the University of Toronto and the University of Washington, suspected these fish might need to chew, as their prey consists of particularly chewy items like insects and mollusks.
On filming the mouths of several subjects in the lab as they ate a variety of soft and hard foods, it became apparent that the stingrays were able to protrude their jaws, move them left and right, and chew on prey with their set of tiny teeth.
Most other animals, aside from mammals, swallow large hunks of food, sometimes grinding them up with the help of gizzards in their guts.
“Chewing is considered an evolutionary innovation in mammals,” the researchers write in Proceedings of the Royal Society B, and its advent probably allowed mammals to diversify their diets.
Similarly, chewing enables these freshwater stingrays to feast on insects — something other ray species don’t even attempt.
The researchers write that this unique feeding behavior likely opened up new dietary options, including those present in foreign habitats, which “may explain why…freshwater rays were successful in making the transition from marine to freshwater environments.”
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