Dolphins are air breathing mammals who, along with whales and porpoises, belong in the order Cetacea.
Like whales, dolphins are descendants of land-dwelling mammals who gradually adapted to life in the sea until they evolved to a point where they could no longer live on land. Although whales and dolphins do not resemble most other mammals, DNA and fossil evidence show that they are most closely related to pigs, hippopotamuses, camels and deer.
Although dolphins are widespread in the seas, most species prefer the warmer waters of the tropic zones. Some, like the right whale dolphin prefer colder climates. During their transition from land to water, their front legs evolved into paddle-like flippers and their rear legs disappeared. Their bodies also acquired a thick insulating layer of blubber, and their nostrils moved from the snout to the top of the head to become a blowhole.
Dolphins have a beak-like snout and a streamlined body superbly adapted for life and speed in the water — one species has been clocked at 37 mph. They eat mostly fish, crustaceans and squid. Some 33 species have been identified.
Dolphins are very friendly, playful, and highly intelligent creatures. They form strong social relationships with close mother-child bonds. A newborn, or calf, will nurse from 11 months to 2 years, and after nursing will stay with its mother for several more years. They live in groups called pods containing five to several hundred individuals.
Dolphins keep in touch by clicks, barks, chattering sounds, screams, and moans, each of which seems to have a special meaning. Like bats, dolphins use echolocation to navigate, locate one another and hunt. Since they must breathe air, dolphins are born tail first instead of head first like land mammals. This helps prevent the newborn from drowning during birth and allows the mother to get the calf quickly to the surface for its first breath of air.
Larrie Stone is a retired Dana College science professor.