Skull shape reflects prey size niche in toothed whales

Abstract

Studies have suggested that the proportions of the rostrum and mandible (from short and broad to elongate and narrow) in toothed whales (odontocetes) may be associated with the size of the prey they consume, yet quantitative data on relationships between skull shape and diet have been lacking. Here, we quantified variation in skull shape in extant toothed whales using 3D geometric morphometric analysis. We then used Phylogenetic Generalized Least Squares (PGLS) regression to examine the relationships between skull shape and quantitative data on minimum, average and maximum prey size. When examining all odontocetes, there were only weak correlations between skull shape and prey size. However, when suction feeding taxa were excluded, prey size was correlated with the size of the predator (predator size vs. max prey size: R² = 0.45) as well as the shape of the cranium (cranial robustness vs. minimum prey size: R² = 0.19) and mandible (mandible robustness vs. minimum prey size: R² = 0.27). Considering the prey capture method (suction feeding vs. raptorial feeding) is therefore important for elucidating relationships that exist between form and function. These findings suggest that cranial morphology is intimately linked to prey size niche in toothed whales within specific functional contexts