Using high-speed videography, Kolmann and his team found that the stingrays chew their food using asymmetrical jaw action. CT-scanning further detected simple teeth in the marine animals.
The finding that these animals chew calls into question one aspect of what supposedly makes humans and mammals unique among other species.
"Chewing is considered an evolutionary innovation in mammals that spurred dietary diversification, allowing exploitation of food sources ranging from insects to grasses," according to the authors. "Dietary flexibility and efficiency made possible by chewing is thought to have contributed to the evolutionary radiation of mammals."
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Stingrays eat a wide variety of prey as well, though. Their diet includes shellfish, fish, insects and more. They manage to eat hard and tough items without the benefit of limbs that can stuff food into their mouth.
Some animals have solved such feasting challenges by using their mouths/beaks to both seize and tear their prey.
"For example, birds and some other archosaurs (such as crocodiles and alligators) use a beak or jaws to seize and rend prey, while a muscular gizzard is used to grind prey further," Kolmann and his team point out.
Stingrays also have a multistep eating process, but it goes as follows: their pectoral fins rapidly flap up, powerful suction draws prey into the stingray's mouth as much as possible, and the stingray chews like crazy in hopes of eating the entire victim.
The hope is that stingrays will some day serve as a model system for better understanding the evolutionary convergence of prey processing and chewing in animals, both on land and in water.
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