Evolution has resulted in the development of both herbivores and carnivores -- but how? What type of food did extinct vertebrates eat? And how can we gain insight into the diets of these creatures? In living animals, we can simply observe what they feed on today. In the case of extinct species, however, researchers rely on morphological or chemical information supplied by fossils. A team has now compiled a reference framework of isotope compositions indicating the type of diet for extant reptiles that represents a useful reference dataset to reconstruct the diet of fossil reptiles.