Flipper (anatomy)
A flipper is a broad, flattened limb adapted for aquatic locomotion. It refers to the fully webbed, swimming appendages of aquatic vertebrates that are not fish.
For the fish appendage, see Fish fin.
In animals with two flippers, such as whales, the flipper refers solely to the forelimbs. In animals with four flippers, such as pinnipeds and sea turtles, one may distinguish fore- and hind-flippers, or pectoral flippers and pelvic flippers.[2][3]
Animals with flippers include penguins (whose flippers are also called wings), cetaceans (e.g., dolphins and whales), pinnipeds (e.g., walruses, earless and eared seals), sirenians (e.g., manatees and dugongs), and marine reptiles such as the sea turtles and the now-extinct plesiosaurs, mosasaurs, ichthyosaurs, and metriorhynchids.
Usage of the terms "fin" and "flipper" is sometimes inconsistent, even in the scientific literature. However, the hydrodynamic control surfaces of fish are always referred to as "fins" and never "flippers". Tetrapod limbs which have evolved into fin-like structures are usually (but not always) called "flippers" rather than fins. The dorsal structure on cetaceans is called the "dorsal fin" and the large cetacean tails are referred to primarily as flukes but occasionally as "caudal fins"; neither of these structures are flippers.
Some flippers are very efficient hydrofoils, analogous to wings (airfoils), used to propel and maneuver through the water with great speed and maneuverability (see Foil). Swimming appendages with the digits still apparent, as in the webbed forefeet of amphibious turtles and platypus, are considered paddles rather than flippers.[3]
Foraging behavior[edit]
Because of the specialization of flippers and their hydrodynamic constraints, it was thought that they were not used to significantly interact with the environment, unlike the legs of terrestrial tetrapods. However, the use of limbs for foraging is documented in marine tetrapods.[13] Use of the flippers for foraging behavior is observed in marine mammals such as walruses, seals, and manatee, and even in reptiles such as sea turtles. Among turtles, observed behaviors include a green turtle holding a jellyfish, a loggerhead rolling a scallop on the sea floor, and a hawksbill turtle pushing against a reef for leverage to rip an anemone loose.[14] Based on presumed limb use in ancestral turtles, these behaviors may have occurred as long ago as 70 million years.[13]