Using the Australian marine-freshwater terapontid fishes as a model system, we examined the role of dietary phenotypic optima in an adaptive macro-evolutionary landscape. Comparative modelling relying on both a priori and data-driven identification of selective regimes suggested multi-peak models as best describing much of the dietary phenotypic landscape of terapontids. Both approaches identified common phenotypic optima for different lineages of marine and freshwater herbivores, and minimal differentiation between carnivores and omnivores, irrespective of their phylogenetic relationships, as the model best describing morphological evolution. Significant correlations also existed between these phenotypic axes and proportions of non-animal dietary items in species’ diets. While simulation results provided evidence for a multi-peak adaptive landscape in the evolution of trophic morphology in terapontids, they could not rule out chance convergence in these adaptive peaks. However, they do provide scope for identifying areas for more detailed, functionally specific study of phenotypic convergence in herbivorous terapontid trophic habits.