The evolution of feeding strategies in phocid seals (Pinnipedia, Phocidae)
Adaptations for feeding underwater were crucial to the success of pinnipeds (seals, sea lions, and walruses) in their transition from terrestrial to aquatic habitats. Extant phocids (true seals) use multiple feeding strategies—biting, filter, and suction feeding—to capture and consume prey, and each strategy is associated with cranial, mandibular, and dental adaptations. However, little is known about feeding strategies in stem pinnipeds. The objectives of this study were to investigate feeding strategies used by some extinct pinnipeds based on cranial and mandibular morphologies and use this framework to examine the evolution of phocid feeding strategies. Three-dimensional cranial and mandibular landmark data were collected from 249 extant and fossil pinnipeds. Principal component analysis and canonical variate analysis were performed to describe the major axes of variation and compare overlap of fossil and extant taxa in morphospace. Stem pinnipeds had morphologies associated with biting and filter feeding. Several fossil taxa were most similar to extant biters, suggesting that biting was a common and important feeding strategy for early phocids. One fossil taxon, Homiphoca capensis, was potentially a filter feeder, because it consistently overlapped with extant filter feeders in cranial morphospace. No fossil taxa had morphological adaptations for suction feeding, indicating that suction feeding is a more derived strategy in phocids. Extant phocids and their ancestors have cranial and mandibular adaptations for multiple feeding strategies, which allowed these animals to move into diverse aquatic niches and likely contributed to their successful transition from terrestrial to aquatic ecosystems.