Every hooked beak is maintained by a prey: Ecological signal in cephalopod beak shape

Beaks are among the few hard parts of coleoid cephalopods and are informative for species identification. Although mandible shape has been shown to be adaptive in many vertebrate taxa, it has been suggested that the shape of coleoid beaks does not bear any ecological signal. Yet, previous studies only explored beak shape in 2D and none have provided an in‐depth investigation of the potential relationship with ecological variables such as habitat use, or diet. The goal of the present study was to understand whether variation in cephalopod beak shape reflects ecology and/or is more driven by phylogenetic relatedness as suggested previously. We imaged 101 lower and 108 upper beaks in 3D using underwater photogrammetry and micro‐CT scanning. Our 3D morphometric analysis conducted on 75 species of cephalopod shows that there is a significant but moderate phylogenetic signal. However, comparative phylogenetically‐informed analyses demonstrate that beak shape is also driven by ecology. We detected significant differences in beak shape between species inhabiting different habitats (pelagic, benthic, or demersal) and of different trophic levels. Our results further suggest that beak shape variation can be summarized along a continuum between two main functions: fast closing versus hard biting. These results provide novel insights into the drivers of beak shape diversity in coleoid cephalopods and suggest that beak shape has evolved adaptively in relation to diet and habitat use