Curly Tails: Rare Occurrence Of Bent Flukes In Free-Ranging Cetaceans

Dorsal fins, pectoral fins, and flukes are among the most important morphological structures of fully aquatic animals, including cetaceans (Fish, 1996). These structures are involved in the pro-cesses of thermoregulation, locomotion, stability, and maneuverability (Scholander & Schevill, 1955; Fish, 1996; Weber et al., 2014; Fish & Lauder, 2017), among others. Flukes particularly play an essential role as a propulsive organ contributing to gross body behavior, and they are of critical relevance in body hydrodynamics (Felts, 1966). In cetaceans, the flukes are composed of a thick skin layer, a subcutaneous blubber layer, a liga-mentous layer, a series of arterio-venous plexuses, and a core of dense fibrous tissue (Felts, 1966; Sun et al., 2010). The ligamentous layer, in particular, is constituted by flexor and extensor tendons that are formed from epaxial and hypaxial muscles that reach the caudal portion (Spearman, 1972; Strickler, 1980). These ligaments are responsible for the movements of the fluke and maintain its flat horizontal shape (Strickler, 1980). The flukes are boneless, being firmer in the center and more flexible at the end with a slight curvature, allowing greater efficiency during movement (Fish, 1998)