From about 40 mya, while Antarctica geographically isolated from the rest of the world, the marine shelf fauna faced a dramatic decrease in water temperatures. Many lineages went extinct, while others adapted and flourished. The Antarctic clade of the amphipod family Iphimediidae was among the successful ones. Ecological niches left vacant by the extinction of competitors might have led to the adaptive radiation of this clade. Antarctic iphimediids present a high interspecific variation in mandible morphology. These specific morphologies were previously examined in a few species which were interpreted as micropredatory browsers, each specializing on a preferred food prey. However, the relationship between mandible morphology and trophic niche remains poorly understood. Here, micro-computed tomography scans of the head region were performed in a range of iphimediid species. Geometric morphometric methods were used to obtain 3D shape data of the mandibular body. Secondly, stable isotope ratios (N, C) were measured as variables describing the trophic ecology of the species. By analyzing morphological variation in a phylogenetic context and assessing possible evolutionary correlations between mandible morphology and trophic ecology, we aimed to (i) evaluate adaptation hypotheses and (ii) inform on the eco-evolutionary causes of phenotypic change.