Ontogenetic and interspecific variation in skull morphology of two closely related species of toad, Bufo bufo and B. spinosus (Anura: Bufonidae)

Using micro-CT and 3D landmark-based geometric morphometrics, I investigated postmetamorphic shape variation in the skull of Bufo bufo and Bufo spinosus, two widespread European toad species with small phenotypic differences. Two ontogenetic series were compared, for a total of 58 individuals. They exhibited similar allometric growth patterns, characterised by cranial widening with relative shortening and dorsoventral compression. However, some interspecific shape divergence was observed, particularly among adults: a relatively shorter skull and a more dorsally extended snout distinguished B. spinosus from B. bufo. This disparity, which gives further support to species separation, can probably be ascribed to changes in the allometric trajectories, and seen in light of the evolutionary history of the two lineages.