Dolphins Essay, Research Paper

Dolphins and porpoises are mammals. They breathe air and give birth to living

young then they suckle. They belong to the order or group of mammals called

cetaceans, which include whales. Dolphins have beaklike mouths. Porpoises have

bunt mouths and are smaller than dolphins. But both dolphins and porpoises are

toothed whales, and their close relatives include the killer, sperm and pilot

whale. Cetaceans are mammals that returned to the sea. Hind legs disappeared and

were replaced by a strongly muscled tail end and flat tail or fluke. The front

legs have evolved into flippers. One primitive specie- the Bouto or the river

dolphin of the Amazon and other southern American rivers- has finger bones that

show clearly in their flippers. Most mammalian hair has also disappeared from

the streamlined body of the cetacean. The nostrils for breathing air have

gradually moved to the forehead and, in the dolphins and porpoises have become

one blow whole, which leads right to the lungs instead of the mouth and throat.

The river living dolphins such as the Bouto must come up for air every 30

seconds, but the ocean dolphins can stay in the water for a few minutes. When

they surface, a great spout of moist, used air is comes out from the blow

wholes. More air is taken in, and they dive again. A dolphin or porpoise baby is

born in the water. The mother and another female dolphins, which acts as a

?nurse?, then rush into the surface for the baby?s first breath of air.

They introduce the baby to the deeper water and longer stays under the water the

first few weeks. At first they return to the surface for the baby to suckle

it?s mothers milk. Usually only one baby is born at a time. It spends a full

year feeding on milk and strays from its mother.