Dolphins
are part of the
toothed whales
. Generally, they are among the smaller
whales
. Most live in salt water
oceans
, but some live in
rivers
? there are
oceanic dolphins
and
river dolphins
. Dolphins are from 1.5 metres (4.9 ft) to 4 metres (13 ft) long, but the largest dolphin, the
killer whale
(or orca), can be up to 8 metres (26 ft) long.
All dolphins live in groups called "pods". They are social animals at all stages of their life. They have some remarkable behaviours. A speeding group of dolphins is a sight to see. They "porpoise" in and out of the water at high speed. The function of this is not known for sure. It may be the fastest movement they are capable of.
[1]
What they eat, almost exclusively, is fish. When they chase fish, the fish go into a "bait ball" to self-protect. In turn, the dolphins attack in a group and eat as many fish as they can.
The name 'dolphin' comes from the Ancient
Greek
δελφ?? (
delphis
) meaning "with a womb", because it was first thought to be a
fish
with a
womb
. It is now known to be a mammal, and quite an intelligent mammal. Dolphins breathe
air
. A dolphin's
nose
is on top of its
head
so the dolphin can easily breathe on the
surface
of the
water
. The skin of a dolphin has no scales. It is soft and smooth. However, it is very firm, due to how much muscle they have. Dolphins use
echolocation
to find their food.
The skin of a bottlenose dolphin is gray, smooth, and rubbery. They are always social. They can help each other fight off predators. Dolphins have fought off
sharks
in this way. They can kill large
sharks
by ramming them over and over again with their snouts and heads. They look after the young, when the mothers need to leave their calves to hunt for food. The young need to breathe more often than the adults, and the food may be in deeper waters.
Oceanic dolphins are
marine
animals living in the sea. They live in all of the
oceans
.
Three of the four species of
river dolphins
live in
fresh water
rivers
. The La Plata dolphin lives in
saltwater
estuaries
and the ocean. Water pollution and the loss of habitat are a threat to some dolphins, especially those living in rivers and estuaries.
Dolphins (and other
cetaceans
) sleep in the water.
[2]
There is danger from animals that eat dolphins.
[3]
Dolphins sleep differently than a person. Dolphins have two sides of their
brain
, which they use to sleep. One side sleeps, while the other side stays awake. Dolphins do things while asleep:
- Dolphins will keep one eye open to watch for animals that eat them while they sleep.
- Dolphins also swim in circles when they are sleeping to look around for danger.
- Dolphins get their nose out of the water to breathe.
Dolphin groups or
species
have their own way of sleeping.
Pinnipeds
, like seals, can sleep like dolphins.
[2]
The
brain
of a dolphin is like a human brain in size and development. Dolphins have reasonable eyesight. They can
watch
a thing in the
water
, and they can see colors, too. They can also see in dark places.
A dolphin's hearing is better than their sight. There are small holes behind the eyes, and they are the ears of a dolphin. Dolphins can hear a
sound
underwater. They can know the
direction
of the sound very well.
Dolphins have long played a role in human culture. Dolphins are common in
Greek mythology
and there are many coins from ancient Greece which feature a man or boy or deity riding on the back of a dolphin.
[4]
The
Ancient Greeks
welcomed dolphins; spotting dolphins riding in a ship’s wake was considered a good omen.
[5]
In
Hindu mythology
, the Ganges River Dolphin is associated with Ganga, the deity of the
Ganges
river.
Dolphin meat is eaten in a few countries, including
Japan
[6]
and
Peru
(where it is referred to as
chancho marino
, or "sea pork"). Japan may be the best-known and most controversial example, but eating dolphin is not that common.
Dolphin therapy is sometimes used for people with mental or physical handicaps. It involves contact with trained dolphins. It is not agreed whether this is any better than the usual treatments.
[7]
Scientists continue to study dolphin therapy.
Some examples:
- Genus
Delphinus
- Genus
Tursiops
- Genus
Orcinus
- Genus
Feresa
- Genus
Pseudorca
- Genus
Globicephala
- Genus
Peponocephala
Wikimedia Commons has media related to
Dolphins
.
- ↑
[1]
BBC footage of dophins at top speed.
- ↑
2.0
2.1
Lyamin
et al
2004. Relationship between sleep and eye movement in cetaceans and pinnipeds.
Archives Italliennes de Biologie
142
: 557?568.
- ↑
Gill, Victoria 2012. Slowest Greenland shark hunts sleeping prey.
BBC Nature
[2]
Archived
2012-06-22 at
Archive-It
- ↑
"Taras"
. Archived from
the original
on February 8, 2007
. Retrieved
October 3,
2010
.
- ↑
Eyers, Jonathan 2011.
Don't shoot the Albatross!: nautical myths and superstitions
. A&C Black, London, UK.
ISBN
978-1-4081-3131-2
- ↑
McCurry, Justin (2009).
"Dolphin slaughter turns sea red as Japan hunting season returns"
.
The Guardian
. London
. Retrieved
May 24,
2010
.
- ↑
Lori Marino, Scott O. Lilienfeld (2007).
"Dolphin-Assisted Therapy: more flawed data and more flawed conclusions"
(PDF)
.
Anthrozoos
.
20
(3): 239?49.
doi
:
10.2752/089279307X224782
.
S2CID
6119940
. Archived from
the original
(PDF)
on February 28, 2008
. Retrieved
February 20,
2008
.
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