In July 2023, researchers from the Pelagos Cetacean Research Institute spotted a rare striped dolphin in the Gulf of Corinth with deformed flippers resembling thumbs. The dolphin, part of a unique mixed-species society in the region, was observed swimming and interacting with its pod despite its unusual flipper morphology. Experts believe the deformity is likely a genetic defect acquired in the womb, possibly resulting from constant interbreeding among the isolated population of around 1,300 striped dolphins in the Gulf. The abnormal flipper shape, resembling thumbs, is considered a rare expression of irregular genes, with the defect affecting both flippers. While cetaceans, including dolphins, possess finger-like bones within their flippers, the photographed dolphin's unique deformity suggests a deviation from the typical developmental process, leading to the absence of certain fingers and associated tissue. Despite this anomaly, the dolphin appears to be thriving in its environment.
Read more about it here:
https://www.livescience.com/animals/dolphins/extremely-rare-dolphin-with-thumbs-photographed-in-greek-gulf