Are Dolphins Mammals?

By John Misachi on February 23 2018 in Environment

Female dolphins give birth to live young ones rather than lay eggs like fish do.
Female dolphins give birth to live young ones rather than lay eggs like fish do.

Dolphins are aquatic animal within the order Cetacea. Although widely distributed, most dolphins prefer warm water of the tropic zones. They feed mainly on small fish but some may feed on large mammals like a seals. In countries such as Japan, dolphins are hunted in an activity known as dolphin drive hunting. Other threats to dolphins include habitat loss, marine pollution, and bycatch. The name “dolphin” is borrowed from Greek word “delphis” which is related to another Greek word “delphus” meaning “womb.” Therefore, the name can be interpreted as “fish with the womb.” A male dolphin is referred to as “bull” while the female “cow,” and a group of dolphins as “school.”

Dolphins Are Mammals

Even though dolphins live in water almost all the time, they are neither fish nor cold blooded but are mammals. Dolphins should not be confused with dolphinfish, popularly known as mahi-mahi which is a common type of surface-dwelling fish. Dolphins are warm-blooded just like other mammal and unlike fish that breathe through the gills, they using the lungs. Dolphins cannot breathe in water lest they drown; rather they frequent the water surface to breath. On the other hand, fish will suffocate above the water surface since their gills are not designed for breathing on the surface. Unlike fish, they possess vertebrae. Dolphins are considered to have evolved from land-dwelling mammals of the artiodactyls order with the closest living relative today being the hippopotamus.

Characteristics of Dolphins

Apart from being a warm-blooded mammal that breathes through the lungs, other several characteristics make it a mammal rather than fish.

Female dolphins give birth to live young ones rather than lay eggs like fish do. The reproductive organs of the dolphins are located on their underside. The copulation takes place belly to belly. The gestation period varies from 11 to 12 months. Females mate only after every two years while the male can mate with several females in a year. They also possess mammary glands which are only present in mammals and feed their calves on milk from the mammary glands.

Also, like most mammals, dolphins have tiny layers of hair around the blowhole. A blowhole is a feature on dolphins that facilitate their breathing. Unlike humans, dolphins do not breathe through the mouth but through the blowhole. Blowhole ensures that the water does not get into the lungs if it accidentally inhales the water while swallowing the prey under water.

Anatomy of Dolphins

A dolphin’s size ranges from 5.6 feet to 31 feet and weighs about 110 pounds. The body is torpedo shaped with a non-flexible neck. The limbs have been modified into flippers. The skull has small eye orbit with the eyes placed on the sides of the head. The teeth are conical shaped and are useful in catching swift prey. Dolphins possess a thick layer of blubber which helps in buoyancy and protects them from predators and energy loss. The primary use of the blubber is to insulate the dolphin from the harsh climate.

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