Toothed whales independently evolve specialized suction feeding without converging on skull shape

Specialized suction feeders independently evolved in several odontocete (toothed whale) lineages, with paradigmatic examples in sperm whales and beaked whales. Although little is known about feeding behavior in most cetacean species, many studies have identified morphological correlates of feeding ecology, such as skull shape. Here, we develop a suction specialization index (SSI) to quantify the extent of suction specialization in 68 extant odontocete taxa. This metric incorporates 10 morphological characters historically associated with suction feeding, including skull and hyoid osteology, dentition, and soft tissue structures. Our analyses show that both SSI and individual morphological characters reliably distinguish suction-feeding odontocetes from other taxa. Reduced dentition, non-occluding teeth/jaws, specialized palate, and weak jaw adductors were the strongest predictors. The blunt, wide rostrum was the weakest predictor. The distribution of SSI in the morphospace demonstrates that lineages of suction-feeding odontocetes specialize without converging on skull shape. Our results suggest that quantifying specialization across a suite of morphological predictors can provide a robust framework for reconstructing feeding ecology in extinct taxa. Our findings also highlight the interplay of convergence and constraint in vertebrate feeding systems, ultimately contributing to a broader understanding of how specializing on feeding behavior (e.g., suction) manifests across many different forms.