Data from: Always chew your food: freshwater stingrays use mastication to process tough insect prey

Chewing, characterized by shearing jaw motions and high-crowned molar teeth, is considered an evolutionary innovation that spurred dietary diversification and evolutionary radiation of mammals. Complex prey-processing behaviours have been thought to be lacking in fishes and other vertebrates, despite the fact that many of these animals feed on tough prey, like insects or even grasses. We investigated prey capture and processing in the insect-feeding freshwater stingray Potamotrygon motoro using high-speed videography. We find that Potamotrygon motoro uses asymmetrical motion of the jaws, effectively chewing, to dismantle insect prey. However, CT scanning suggests that this species has simple teeth. These findings suggest that in contrast to mammalian chewing, asymmetrical jaw action is sufficient for mastication in other vertebrates. We also determined that prey capture in these rays occurs through rapid uplift of the pectoral fins, sucking prey beneath the ray's body, thereby dissociating the jaws from a prey capture role. We suggest that the decoupling of prey capture and processing facilitated the evolution of a highly kinetic feeding apparatus in batoid fishes, giving these animals an ability to consume a wide variety of prey, including molluscs, fishes, aquatic insect larvae and crustaceans. We propose Potamotrygon as a model system for understanding evolutionary convergence of prey processing and chewing in vertebrates.以剪切式颌部运动与高冠臼齿为典型特征的咀嚼行为，被视作推动哺乳类饮食多样化与演化辐射的关键演化创新。既往研究普遍认为，鱼类及其他脊椎动物缺乏复杂的猎物处理行为，尽管这类动物中的多数均以昆虫乃至草本植物等坚硬猎物为食。 本研究借助高速摄像技术，对以昆虫为食的淡水魟（Potamotrygon motoro）的猎物捕获与处理过程进行了系统探究。研究结果显示，淡水魟（Potamotrygon motoro）通过颌部的不对称运动实现高效咀嚼，以此拆解昆虫猎物。但计算机断层扫描（CT）结果表明，该物种的齿列结构相对简单。上述发现表明，与哺乳类的咀嚼机制不同，其他脊椎动物仅需依靠不对称颌部运动即可完成咀嚼过程。 本研究同时证实，这类魟鱼的猎物捕获通过胸鳍快速抬升、将猎物吸至体下方完成，这使得颌部脱离了猎物捕获的功能定位。我们认为，猎物捕获与处理的功能解耦，推动鳐总目鱼类演化出高活动性的摄食器官，赋予这类动物取食软体动物、鱼类、水生昆虫幼虫及甲壳类等多样猎物的能力。本研究提出，可将淡水魟（Potamotrygon motoro）作为探究脊椎动物猎物处理与咀嚼行为演化趋同的模式实验系统。