Cross-species applicability of a bone-ageing method in delphinids

Abstract Radiographic evaluation of flipper ossification is a reliable technique for age estimation in bottlenose dolphins (Tursiops truncatus), although its applicability to other odontocetes remains untested. Interspecific differences in flipper morphology and bone development may limit transferability or require adjustments for robust application. This study applies the bottlenose dolphin framework to common dolphins (Delphinus delphis) to characterise developmental patterns, describe morphological differences and evaluate the interspecies application of this method. Radiographs from 137 common dolphins aged 0–31 years were examined, with bone maturation scored at 16 anatomical sites on the pectoral flipper. Several differences were identified, including bilateral asymmetry between left and right flippers and the need to adjust long and delta bone scoring systems due to interspecific variation in bone maturation. Despite these differences, reproducibility between observers was high, and ossification scores correlated strongly with age, underscoring the reliability of the method. This study provides the groundwork for a species-specific bone ageing model for common dolphins by addressing interspecific variation in skeletal maturation. One caveat concerns the subtle expression of degenerative changes in this species compared with bottlenose dolphins, which may limit age estimation precision in older individuals but is unlikely to affect accuracy across most of the lifespan. Thus, our findings provide the first evidence that, despite morphological differences, the method can be successfully applied to common dolphins.