their mobility which provides three degrees of freedom. Flippers on humpback whales (Megaptera novaeangliae) have non-smooth leading edges, yet demonstrate superior fluid dynamics to the characteristically smooth leading edges of artificial wings, turbines and other kinds of blades. The whale's surprising dexterity is due primarily to its non-conventional flippers, which have large, irregular looking bumps called tubercles across their leading edges. The tubercles break up the passage of water, maintaining even channels of the fast-moving water, limiting turbulence and providing greater maneuverability. The foreflippers used by the pinnipeds act as oscillatory hydrofoils. Both fore and hind flippers are used for turning. A 2007 study of Steller's sea lion found that a majority of thrust was produced during the drive phase of the fore flipper stroke cycle. Although previous findings on eared seals suggested that thrust was generated by the initial outward movement of the fore flippers or the terminal drag-based paddling phase, the 2007 study found that little or no thrust was generated during those phases. Swimming performance in sea lions is modulated by changes in the duration and intensity of movements without changing their sequence. Using criteria based on velocity and the minimum radius of turns, pinnipeds' maneuverability is superior to cetaceans but inferior to many fish. Evolution of flippers Marine mammals have evolved several times, developing similar flippers. The forelimbs of cetaceans, pinnipeds, and sirenians presents a classic example of convergent evolution. There is widespread convergence at the gene level. Distinct substitutions in common genes created various aquatic adaptations, most of which constitute parallel evolution because the substitutions in question are not unique to those animals. When comparing cetaceans to pinnipeds to sirenians, 133 parallel amino acid substitutions occur. Comparing and contrasting cetaceans-pinnipeds, cetaceans-sirenians, and pinnipeds-sirenians, 2,351, 7,684, and 2,579 substitutions occur, respectively. Digit processes Whales and their relatives have a soft tissue flipper that encases most of the forelimb, and elongated digits with an increased number of phalanges. Hyperphalangy is an increase in the number of phalanges beyond the plesiomorphic mammal condition of three phalanges-per-digit. This trait is characteristic of secondarily aquatic vertebrates with flippers. Hyperphalangy was present among extinct ichthyosaurs, plesiosaurs, and mosasaurs. Cetaceans are the sole mammals to have evolved hyperphalangy. Though the flippers of modern cetaceans are not correctly described as webbed feet, the intermediate webbed limbs of ancient semiaquatic cetaceans may be described as such. The presence of interdigital webbing within the fossils