Stingrays found to chew their food before swallowing

A stingray’s mouth. Photo Daniela Duncan

September 14^th, 2016 (Bob Yirka). A team of researchers from the University of Toronto and the University of Washington has discovered that at least one species of stingray chews its food before swallowing it. In their paper published in the journal Proceedings of the Royal Society B, the team describes their study of the creatures using high-speed video technology and what they learned about the platter-shaped predators.

Up till now, scientists have assumed that mammals are the only creatures that chew their food before they swallow it—but this, the researchers note, depends in part on how you define chewing. Birds, they note, have a gizzard for grinding up food, though technically it is not chewing in the usual sense, though similar. In this new effort, the research team has found that the ocellate river stingray, which lives in the Amazon River, chews its food in very human-like ways.

Intrigued when they learned that the stingrays often eat prey that would seem to require chewing such as insects and mollusks, the team obtained several samples of them for study in their lab. They placed them in a tank with a see-through glass bottom, as the stingray mouth is on its underside. The researchers then filmed them as they captured three kinds of food—soft, medium and hard—chewed it, and then swallowed it. More specifically, they found that the stingrays first grabbed their prey after pulling it in using suction they created by undulating their bodies, and then moved the left and right parts of their jaws back and forth to create multiple angles for biting and tearing. They found that the stingrays also moved their lower and upper jaws independently. Taken together, the chewing action very much resembles human and other mammal mastication. To make sure that the jaw actions were what they seemed, the researchers also performed CT scans on the stingrays and found that the chewing action worked in concert with small teeth.

The finding by the team suggests that chewing by humans and other animals is not nearly as unique as has been thought—they plan to study other stingray species to see if they too chew their food.

Citation : Always chew your food: freshwater stingrays use mastication to process tough insect prey. Matthew A. Kolmann et al. Proceedings of the Royal Society B, Published 14 September 2016. rspb.royalsocietypublishing.org/lookup/doi/10.1098/rspb.2016.1392

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