My thesis research aims to study, in a phylogenetic context, the different features related to diet change and to highlight a precedence in the evolutionary process. The main objective is to understand how the change in the diet can be reflected in the anatomy. How can taxa shift from a diet to another? Is it always in the same way? How does the shift process take place? What are the functional, morphological, physiological and behavioural differences between herbivores, omnivores and carnivores of a same phylogenetic group? With a large diversity of shape (morphology) and diet (ecology), the piranhas’ family (Serrasalmidae - 95 species) is a suitable monophyletic group and an excellent opportunity to investigate this questioning. In a framework of comparative functional morphology, the research is organized into four main studies: (1) functional study of the feeding mechanism using measurements of bite force and biomechanical characters at the level of jaws and teeth; (2) morphological study of the cephalic region, upper and lower jaws, jaw muscle and buccal teeth using diverse methods (dissection, µCT scan, geometric morphometry, scanning and transmission electron microscopy, nanoindentation); (3) study of the sensory organs (lateral line, vision and olfaction systems) from physiological (sensory capacities) and morphological points of view (shape and arrangement of subunits of each system); and (4) synthesis and integration of the results by taking into account the phylogeny of the family. This multidisciplinary research will provide theory on the macroevolution of organisms in response to ecological changes.