Interesting research findings have come out of the University of Toronto regarding the food consumption habits of freshwater stingrays commonly found in the Amazon.

According to the research, some groups of freshwater stingrays show the rare trait of eating food like mammals by chewing them hard and then shearing it sideways.

The significant finding, which was published in the Proceedings of the Royal Society B, sheds light on the eating habits of stingrays living in the lakes and rivers throughout the Amazon, stretching from eastern Brazil to the Andes in Peru.

Credit for the pioneering study goes to Matthew Kolmann from the University of Toronto. In his painstaking research, Kolmann captured the rare footages of stingrays' eating style by using CT scans and high-speed video recording.

Kolmann studied two groups of stingrays, Potamotrygon motoro and Potamotrygon orbignyi. Between the two groups, the P. motoro eats fish, crabs, insects and prawns while the P. orbignyi eats only insects.

Discussing the discovery, Kolmann explains that the P. motoro stingray extends its jaws away from its skull as it feeds, breaking down its food from side to side.

"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," Kolmann says.

Chewing has been described as a phenomenon that is peculiar and unique to mammals, an ability the land-dwelling vertebrates acquired 65 million years ago. The mechanism helps mammals consume robust prey for maintaining their endothermic metabolism.

"Both mammals and these stingrays - two groups that have little to do with each other developed a similar solution," the lead researcher notes.

Stingrays use the front of their head to draw water and prey, trapping it with their fins, explains Kolmann. They then extend their jaw toward the prey, rapidly stripping and cutting it apart. Kolmann adds that the stingrays don't use their mouth to grab their prey, which may have caused parts of the mouth to lose that specific ability and develop an unusual chewing behavior.

Rationale Of Chewing

Kolmann argues that freshwater stingrays have undergone progressive evolution for eating insects and it came more as a compulsion. The reasoning is that when stingrays landed in the Amazon some 40 million years ago, aquatic insect larvae might have been plenty and the most nutritious food to be found then. Because these insects were difficult to break down, the stingrays slowly resorted to chewing them.

The new research is expected to throw more light into the bio-materials mechanism as to how non-mammals break down their food.

Photo: Bernard Dupont | Flickr