The skeleton is often the only remaining structure of the Guiana dolphin, Sotalia guianensis, after decomposition of carcasses. This study investigates the bone development of Guiana dolphins beached on the coastline of the state of Espírito Santo, Brazil. External measurements of 43 thoracic limbs were obtained. Internal structures (radius, ulna, and humerus) were also measured. Dual-energy X-ray absorptiometry (DXA) was used to evaluate bone mass. The variables concerning the thoracic limb were tested using the Akaike information criterion to scale the best growth model when correlated with age and by the allometric model when they were correlated with total body length. The efficacy of DXA was also tested. The Brody growth model (best fit) showed that the thoracic limb stopped growing around the age of 2, while total body length ceased to grow at the age of 5.5. The thoracic limb presented early growth (negative allometry) compared with total body length. The methodology used to measure bone mass was efficient when considering ash weight. No difference in bone density was observed between the right and the left forelimb (P > 0.05), male and female (P > 0.05), or between dolphins found in the 3 sites we monitored. The deposition of bone mass was high in the early stages of life, and stabilization occurred at around the age of 13.