Freshwater stingray found to munch tough food just like a goat

8 pictures

Kolmann used a combination of high-speed video and CT scans to see how two freshwater rays from the Amazon go about their business at mealtime

View gallery - 8 images

Many millions of years ago, we mammals veered from the path of Earth's other inhabitants by evolving a unique skill – the capacity to chew. This newfound ability to chow down on tough foods powered our warm-blooded metabolisms and is credited with much of our success over the past 60-70 million years. But recently, scientists are discovering some unexpected parallels in the animal kingdom, the latest example being an Amazonian freshwater stingray that likes to nibble away on aquatic insects.

Because of their gritty exoskeletons, insects are mighty tough to digest without first chewing to tear them apart. This was thought to have kept aquatic insect larvae off the menu for elasmobranchs, a family of non-chewing fish that includes sharks, skates and rays. So when Matthew Kolmann, a biologist at the University of Toronto, found out that that two species of freshwater stingrays do in fact feed on aquatic insects, naturally he had a few questions.

Kolmann used a combination of high-speed video and CT scans to see how the Potamotrygon orbignyi and Potamotrygon motoro, two freshwater rays from the Amazon, go about their business at mealtime. He found that as they eat, they actually protrude their jaws away from the skull and move them side to side, tearing their food into pieces in much the same way that some mammals would do.

¨It's pretty extraordinary when you think about it – here's this bizarre-looking fish from the Amazon that evolved these behaviors separately from mammals, but chews its food just like a cow or a goat," says Kolmann.

Kolmann says that freshwater stingrays evolved to chew insects as a means of survival. When they ventured into the Amazon between 20 and 40 million years ago, nutritious aquatic insect larvae were everywhere, but they weren't really a dining option for other freshwater inhabitants because of the reasons outlined above. So feeding on insects helped the Potamotrygon orbignyi and Potamotrygon motoro avoid competition for food.

While plenty of non-mammals can do damage with their teeth (hello sharks), none were thought to engage in the act of chewing. Recent research, however, has revealed that a few unlikely animals adopted the behavior to help digest tougher sources of food. This includes carp, lizards and also raised the possibility that some dinosaurs were partial to the activity. This is, however, is the first time chewing has been observed in sharks and stingrays.

The team's research was published in the journal Proceedings of the Royal Society B, and you can see the (kind of creepy) chewing in action in the video below.

View gallery - 8 images

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