Dolphin is a common name of aquatic mammals within the infraorder Cetacea. The term dolphin usually refers to the extant families Delphinidae the oceanic dolphins , Platanistidae the Indian river dolphins , Iniidae the New World river dolphins , and Pontoporiidae the brackish dolphins , and the extinct Lipotidae baiji or Chinese river dolphin. There are 40 extant species named as dolphins. Dolphins range in size from the 1. Several species exhibit sexual dimorphism , in that the males are larger than females. They have streamlined bodies and two limbs that are modified into flippers. They have well-developed hearing which is adapted for both air and water and is so well developed that some can survive even if they are blind. Some species are well adapted for diving to great depths. They have a layer of fat, or blubber , under the skin to keep warm in the cold water.
Behavior and reproduction
Dolphins are highly intelligent marine mammals and are part of the family of toothed whales that includes orcas and pilot whales. They are found worldwide, mostly in shallow seas of the continental shelves, and are carnivores, mostly eating fish and squid. Dolphin coloration varies, but they are generally gray in color with darker backs than the rest of their bodies. As climate change causes the seas and oceans to warm, dolphins are being seen more frequently in colder waters outside their historic ranges. Scientists are concerned that dolphins will have difficulty adapting as quickly as necessary to find new feeding grounds to sustain their populations. Some dolphins that live in areas where rivers and oceans meet, known as brackish waters, are also losing habitat as ocean levels rise due to global warming.
E ven though they live in the ocean all of the time, dolphins are mammals, not fish. Also, dolphins are different than "dolphinfish," which are also known as mahi-mahi. Like every mammal, dolphins are warm blooded. Unlike fish, who breathe through gills, dolphins breathe air using lungs. Dolphins must make frequent trips to the surface of the water to catch a breath.
All rights reserved. Most dolphins are marine and live in the ocean or brackish waters along coastlines. There are a few species, however, like the South Asian river dolphin and the Amazon river dolphin, or boto , that live in freshwater streams and rivers.