Why is shark fins and dolphin fins analogous?
Dolphins evolved from an artiodactyl, a land mammal with even number of toes. The closest relative of all the whales and dolphins is the hippo. Hippos do not have fins. No artiodactyl has fins. Neither does the ancestors of whales, such as Pakicetus. That means whales evolved their fins independently of sharks. Structures that evolved independently in different lineages are not homologous but analogous. Further, they are anatomicallly different. The dorsal fins of sharks are rigid, and supported by cartilage internally. The dorsal fins of dolphins have no internal support. They are held erect by collagen fibers in the outside skin only. Captive killer whales (a sort of dolphin) often have dorsal fins that flop because of gravity and the shallow pool they spend their time in, The shallow water does not provide enough buoyancy for the dorsal fins, causing them to bend under their own weight. The pectoral fins of sharks and dolphins, however, are homologous. However, the dolphin’s pectora
