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The word "animal" comes from the Latin word animale, neuter of animalis, and is derived from anima, meaning vital breath or soul. In everyday colloquial usage, the word usually refers to non-human animals. The biological definition of the word refers to all members of the Kingdom Animalia. Therefore, when the word "animal" is used in a biological context, humans are included.
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About Dolphins

Posted by WishbonE at 2:52 AM

Friday, July 25, 2008

About Dolphins

Dolphins belong to a group of mammals called cetaceans. Cetaceans include all whales and dolphins. Some cetaceans, like the blue whale, are baleen whales and have horny plates hanging from their upper jaw that are used to strain food from the ocean. Others, like dolphins, are "toothed whales." There are almost forty species of dolphin in seventeen genera. They vary in size from 1.2 metres (4 ft) and 40 kilograms (88 lb) (Maui's Dolphin), up to 9.5 m (30 ft) and ten tonnes (the Orca or Killer Whale). They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating fish and squid. The family Delphinidae is the largest in the Cetacea, and relatively recent: dolphins evolved about ten million years ago, during the Miocene. Dolphins are considered to be amongst the most intelligent of animals and their often friendly appearance and seemingly playful attitude have made them popular in human culture. Dolphins are the "humans of the sea" ~ i.e., thinking mammals of the whale (Cetace) family, filling the ranks between whales and porpoises, just like humans fill the gap between gorillas and spider monkeys. Dolphins, like you and me, are mammals. They have teeth, are warm-blooded, have a four-chambered heart, and nurse their young from mammary glands. Dolphins also have hair — but not very much! The dolphin's name can therefore be interpreted as meaning "a 'fish' with a womb". he name was transmitted via the Latin delphinus, Middle Latin dolfinus and the Old French daulphin, which reintroduced the ph into the word.

  • Family Delphinidae (oceanic dolphins)
  • Platanistoidea (oceanic and river dolphins)
  • Odontoceti (toothed whales; these include the above families and some others)
  • Bottlenose Dolphin, the most common and familiar species of dolphin.

The most familiar dolphin face is that of the Bottlenose Dolphin (Tursiops truncatus) of "FLIPPER" fame, with its distinctive curved "smile". Bottlenose dolphin are friendly, and readily co-operate in performing stunts. On TV, in the movies, and at marine parks, the dolphin you are most likely to see performing is a Bottlenose Dolphin. Bottlenose dolphin replace their outer layer of skin every two hours, so you won't see a Bottlenose dolphin without scars! Like whales, dolphins have a whale of time slapping their tails on the water trying to make the loudest possible noise. And, like teenagers around the world, one dolphin can drive the marine world crazy by slapping its flukes against the water as many as 20 times in a row! The speed of sound is about 4 times greater underwater, a fact you can pass on to your parents the next time they complain about the noise you make! Dolphin also communicate by making a clicking noise with their blowhole ~ as many as 800 ultrasonic clicks per second! This communication system makes it easy for them to precisely locate enemies - and food!

Dolphins are often regarded as one of Earth's most intelligent animals, though it is hard to say just how intelligent dolphins are, as comparisons of species' relative intelligence are complicated by differences in sensory apparatus, response modes, and nature of cognition. Furthermore, the difficulty and expense of doing experimental work with large aquatics means that some tests which could yield meaningful results still have not been carried out, or have been carried out with inadequate sample size and methodology. Dolphin behaviour has been studied extensively by humans however, both in captivity and in the wild. Dolphins are social, living in pods (also called "schools") of up to a dozen individuals. In places with a high abundance of food, pods can join temporarily, forming an aggregation called a superpod; such groupings may exceed a thousand dolphins. The individuals communicate using a variety of clicks, whistles and other vocalizations. They also use ultrasonic sounds for echolocation. Membership in pods is not rigid; interchange is common. However, the cetaceans can establish strong bonds between each other. This leads to them staying with injured or ill individuals, even actively helping them to breathe by bringing them to the surface if needed. Dolphins occasionally leap above the water surface, sometimes performing acrobatic figures. Scientists are not always quite certain about the purpose of this behaviour and the reason for it may vary; it could be to locate schools of fish by looking at above-water signs like feeding birds, they could be communicating to other dolphins to join a hunt, attempting to dislodge parasites, or simply doing it for fun. Play is a fairly important part of dolphins' lives, and they can be observed playing with seaweed or play-fighting with other dolphins. At times they also harass other local creatures, like seabirds and turtles. Dolphins also seem to enjoy riding waves and frequently 'surf' coastal swells and the bow waves of boats. Occasionally, they're also willing to playfully interact with human swimmers.

Dolphins have a streamlined fusiform body, adapted for fast swimming. The tail fin, called the fluke, is used for propulsion, while the pectoral fins together with the entire tail section provide directional control. The dorsal fin, in those species that have one, provides stability while swimming. Most dolphins have acute eyesight, both in and out of the water, and their sense of hearing is superior to that of humans. Though they have a small ear opening on each side of their head, it is believed that hearing underwater is also if not exclusively done with the lower jaw which conducts the sound vibrations to the middle ear via a fat-filled cavity in the lower jaw bone. Hearing is also used for echolocation, which seems to be an ability all dolphins have. It is believed that their teeth are arranged in a way that works as an array or antenna to receive the incoming sound and make it easier for them to pinpoint the exact location of an object. Because dolphins need to come up to the surface to breathe and have to be alert for possible predators, they do not sleep in the same way land mammals do. Generally, dolphins sleep with only one brain hemisphere in slow-wave sleep at a time, thus maintaining some amount of consciousness required to breathe and keeping one eye open to keep a watch out for possible threats. The earlier stages of sleep can be observed in both hemispheres of the brain, however.

Dolphins are an increasingly popular choice of animal-assisted therapy for psychological problems and developmental disabilities. For example, a 2005 study with 30 participants found it was an effective treatment for mild to moderate depression. However, this study was criticized on several grounds; for example, it is not known whether dolphins are more effective than common pets. Reviews of this and other published dolphin-assisted therapy (DAT) studies have found important methodological flaws and have concluded that there is no compelling scientific evidence that DAT is a legitimate therapy or that it affords any more than fleeting improvements in mood. Dolphins have few natural enemies, some species or specific populations having none at all making them apex predators. For most smaller species of dolphins, only a few larger species of shark such as the bull shark, dusky shark, tiger shark and great white shark are a potential risk, especially for calves. Some of the larger dolphin species such as Orcas may also prey on some of the smaller dolphin species, but this seems rare. Dolphins may also suffer from a wide variety of diseases and parasites. Some dolphin species face an uncertain future, especially some of the river dolphin species such as the Amazon River Dolphin, and the Ganges and Yangtze River Dolphin, all of which are critically or seriously endangered. A 2006 survey found no individuals of the Yangtze River Dolphin, leading to the conclusion that the species is now functionally extinct. Contamination of environment - the oceans, seas, and rivers - is an issue of concern, especially pesticides, heavy metals, plastics, and other industrial and agricultural pollutants which do not disintegrate rapidly in the environment are reducing dolphin populations, and resulting in dolphins building up unusually high levels of contaminants. Injuries or deaths due to collisions with boats, especially their propellers, are also common. Various fishing methods, most notably purse seine fishing for tuna and the use of drift and gill nets, results in a large amounts of dolphins being killed inadvertently.

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