Posts Tagged ‘evolution’

The huge gang of dolphins

// March 12th, 2009 // View Comments // About Dolphins

By Melissa Bañuelos

Part I

We are used to dolphin faces in waterparks and aquariums, we watched the movie “Flipper”, we know how to draw a dolphin, we know how to identify it from sharks and other marine animals, but most of the time we are just talking about one type of dolphin called “the bottle nose dolphin”.

Contributing to the awesome variety of our Planet, there are different dolphin species: 37 types of oceanic dolphins, 4 river dolphins and 6 types of porpoises. In this article we will talk about the most common species and their main characteristics that will be useful to identify them. Next time you see a dolphin you will know which one of all the cousins is greeting you, probably it won’t be Flipper.




atlantic-spotted-dolphin
Atlantic Spotted Dolphin: The upper body of the Atlantic spotted dolphin is a dark gray color and they develop spots as they get older. They have a chunky beak with a white spot at the end.








hump-backed-dolphin
Hump Backed Dolphin: They are generally gray with a lighter color along their underside. When they are young they don’t have a hump, but as they grow older the hump will appear infront of the dorsal fin. Sometimes the hump can be a third of the full body length.






atlantic-withe-sided-dolphin
Atlantic White-sided Dolphin: Black on the back, with dark grey lines and a long white oval blaze below the dorsal fin, above the blaze there is an ochre band and their belly is white. They have a black ring around the eyes.






bottlenose-dolphinBottlenose dolphin: As we have mentioned, this is one of the most common species. They are truly flexible in their behavior and docile with humans. Their short beak has the shape of a bottle that appears to be floating on the water.






Part II: The Huge Ganng of Dolphins

Echolocation

// February 10th, 2009 // View Comments // About Dolphins

Echolocation, also called biosonar, is the biological sonar used by several animals such as dolphins, shrews, most bats and whales. It is important to marine mammals because it allows them to navigate and feed in the dark at night and in deep or murky water where it isn’t easy to see.

echolocation
Toothed whales emit a focused beam of high-frequency clicks. Sounds are generated by passing air from the bony nares through the phonic lips. These sounds are reflected by the dense concave bone of the cranium and an air sac at its base. The focused beam is modulated by a large fatty organ known as the ‘melon’. This acts like an acoustic lens because it is composed of lipids of differing densities. Most toothed whales use clicks in series, or click train, for echolocation. Toothed whale whistles do not appear to be used in echolocation. Different rates of click production in a click train result on familiar barks, squeals and growls of the bottlenose dolphin.

The major areas of sound reception are the fat-filled cavities of the lower jaw bones. Sounds are received and conducted through the lower jaw to the middle ear, inner ear, and then to hearing centers in the brain via the auditory nerve. Lateral sound may be received through fatty lobes surrounding the ears with a similar acoustic density to the bone. The brain receives the sound waves in the form of nerve impulses, which relay the messages of sound and enable the dolphin to interpret the sound’s meaning.

Bottlenose dolphins are able to learn and later recognize the echo signatures returned by preferred prey species.