About the Dolphins - Projeto Golfinho Rotador

Origin and Evolution

Dolphins belong to the Mammalia Class, Theria Subclass, Eutheria Infraclass (placental), Cetartiodactyla Suborder, which includes the Arctiodactyla as: cattle, deer, camels, hippos and Cetaceans. The term Cetancodonta has been used to group the evolutionary lineage of cetaceans and hippos. The term “cetacean” comes from the Greek, “ketos” meaning whale or sea monster.

Cetaceans have a single origin, a process known as monophyly. Studies indicate that modern cetaceans evolved from terrestrial animals, which colonized estuarine areas about 55 million years ago. The transition to aquatic life seems to have occurred in the region that today corresponds to the Mediterranean Sea and the Asian subcontinent.

The Cetacea Order includes three Suborders. Archeoceti is made up of extinct species. The Mysticeti Suborder groups the true whales, which, instead of teeth, have baleen plates in their mouth. And the Odontoceti Suborder, which comprises cetaceans with teeth, like dolphins.

The Mysticeti Suborder comprises four families: Balaenopteridae (whales, such as the humpback whale and the minke whale), Balaenidae (whale-whale and bowhead whale), Eschrictiidae (gray whale) and Neobalaenidae (pygmy whale).

The Odontoceti Suborder is divided into 10 families: Ziphiidae (beaked whales), Physeteridae (sperm whale), Kogiidae (Dwarf sperm whales), Platanistidae (Asian river dolphins), Pontoporiidae (La Plata dolphin), Lipotidae (baiji), Iniidae (pink rive dolphin), Phocoenidae (porpoises) and Monodontidae (narwhal and beluga). We consider as dolphins the members of the Delphinidae, Iniidae and Pontoporiidae families.

Dolphins are found in all marine environments in the world, except for the poles. There are species of dolphins that live in rivers, on the coast entering estuaries, in open seas and in some cases they have a wide distribution.

In Brazil, the most easily found dolphins are the pink river-dolphins, la plata, tucuxi, estuarine dolphins, bottlenose dolphins and spinner dolphins.

Anatomy

Dolphins have evolved anatomically to live in the aquatic environment, mainly in terms of external morphology, acquiring a more hydrodynamic shape and becoming the most adapted mammals to water.

Internally, dolphins have an anatomy very similar to that of other mammals, with the same organs and functions. The internal adaptations were more physiological for diving and freshwater life.

Breath

Dolphins are mammals and breathe air into their lungs, like we do! Dolphins breathe through a blowhole, which forces them to come to the surface to accomplish gaseous exchanges. The blowhole works as a valve that opens when the dolphin rises to breathe and closes before it submerges.

Osmoregulation

Dolphins’ blood is a lot less concentrated (hypotonic) and their urine much denser (hypertonic) than seawater, due to the high efficiency of their kidneys. Dolphins do not drink seawater but they absorb the amount of fresh water through the digestion of their preys. Another source of water for dolphins, as in desert mammals, is metabolic water, obtained from the metabolism of food molecules, when hydrogen atoms combine with oxygen atoms to produce H₂O.

Vision

Like humans, dolphins have eyes that have cones, rods and retinal photoreceptor cells.

Dolphins distinguish colors, respond to light, see out of the water, and use vision to identify other group members, boats, predators, and obstacles.

An extension, like a curtain, on the upper edge of the iris, descends on the pupil forming two small pupils. The double pupil gives dolphins several advantages, such as binocular vision in each eye.

Ecolocation

Dolphins have a guidance and localization system known as echolocation. Through it, high frequency sounds, inaudible to the human ear, are produced by the vibration of the air ducts and directed out through the melon, a mass of adipose tissue located between the rostrum and the blowhole. The melon also acts to direct sound waves and changes the frequency and length of them.

When sounds reach an object, the echo returns to the dolphin that captures them through the jaw and ear being transmitted to the brain that in turn analyzes them for location, shape, texture and constitution.

Dolphins use echolocation to locate an object, detect subtle differences in objects, mislead shoals of fish or divide the shoal.

Intelligence

Due to the complexity of their social structures, their communication systems and the morphological and physiological characteristics of their brain, dolphins are considered to be very intelligent animals.

Proportionally, in relation to the weight and volume of its size, the spinner dolphin’s brain is the third largest, with about 1.5 kg, and the human brain is the sixth. The associative cortex of the dolphin, the part specialized in abstract and conceptual thinking, is larger than that of the human being. The spinner dolphin’s brain has had the same characteristics for at least 30 million years.

Playful side

The relationship between men and dolphins has given rise to myths and legends about these animals. In most cultures, dolphins are considered as sacred animals and not dangerous and not used as food.

The history of mankind is replete with references of the interaction between men and dolphins, from Greek mythology to Amazon legends, where the figure of the dolphin is always linked to sexuality, fertility and intellectuality, attractive characteristics and sympathetic to the human species.

Strategy

A metaphor created by Dudley Lynch and Paul Kordis of the Brain Technologies Institute divides men into three classes of animals: carps, sharks and dolphins.

A carp, when attacked, does not move away, retaliate or fight. It accepts its destiny. Carps are people who play the lose-win, lose so that the other can win.

A shark believes that we live in a world of scarcity and because of this, it uses the strategy intended to produce a personal win, whatever the cost. Sharks play the win-lose, they always have to win, not caring that the other lose.

The dolphin’s strategy is to cultivate overall confidence: in yourself, in others and in the entire universe. They play the win/win game. They know how to do more with less, to live in the long term and, at the same time, live aware in the present in short term. According to the metaphor, dolphins think that: “The Universe is potentially an abundant place, there is enough for everybody. For me to win, you do not have to lose.”

Environmental impacts

Due to the abundance of resources the whales offer, they have been caught for several centuries. Species such as the blue whale, fin, sei, and sperm whale have reached threatening population reductions by the middle of the last century. Fortunately, in the 1970s, a global whale protection movement began which culminated in the announcement of a world moratorium on commercial whale hunting (whaling) in the following decade. Intentional capture of dolphins is reduced, but by-catch (unintentionally and unavoidably) and incidental capture (which could have been avoided) is a threat to the conservation of these animals.

Another harmful effect of human action on cetaceans comes from the pollution of the oceans through harmful substances such as pesticides and heavy metals. In Brazil, the contamination of cetaceans by pollution, especially by heavy metals, has already been verified for several species, such as Guiana dolphin and La Plata dolphin. The high amount of litter in the sea, mainly plastic and waste fishing equipment, has been a problem for dolphins. The similarity of appearance between plastics and squid or jellyfish confuses the dolphins, which can lead them to ingest these materials. Remains of fishing gear such as lines and pieces of nets are often observed curled up and slowly cutting off the body of cetaceans.

Seismic prospecting for oil and gas has caused serious problems for cetaceans, as the air guns used in this activity cause explosions that affect the cetacean orientation system, especially the tympanic bullae and the echolocation system.

Although recently tourism activities to watch cetaceans has been also a source of impact on these animals, dolphin and whale watching plays an important educational and developmental role in the non-lethal use of cetaceans but it needs to be carried out under rules of approach to these animals.

Origin and Evolution

Anatomy

Breath

Osmoregulation

Vision

Ecolocation

Intelligence

Playful side

Strategy

Environmental impacts

Sponsor

Execution

Origin and Evolution

Anatomy

Breath

Osmoregulation

Vision

Ecolocation

Intelligence

Playful side

Strategy

Environmental impacts

Sponsor

Execution

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