Dolphins are marine mammals that are closely related to whales and porpoises.There are almost forty species of dolphin in seventeen genera.They vary in size from 1.2m(4ft) and 40kg(90lb)[Mauli's dolphin],up to 9.5m[30ft] and 10tonnes[9.8 LT; 11 ST][the orca or killer whales]. 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 Cetacean order, and relatively recent: dolphins evolved about ten million years ago,during the Micone.
Dolphins are among the most intelligent animals and their often friendly appearance and seemingly playful attitude have made them popular in human culture.
Dolphins,along with whales and porpoises, are descendants of terrestrial mammals,most likely of the Artiodactyl order.The ancestors of the modern day dolphins entered the water roughly fifty million years ago, in the Eocene epoch.
Most of dolphins have acute eyesight,both in and out of the water,both in and out of the water,and they can hear frequencies ten times or more above the upper limit of adult human hearing. 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 sound to the middle ear via a fat-filled cavity in the lower jaw bone..
Hearing is also used for echolocation,which all dolphins have. It is believed that dolphin teeth function as an antenna to recieve incoming sound and to pinpoint the exact location of an object .The dolphin's sense of touch is also well-developed, with free nerve endings densely packed in the skin , especially around the SNOUT , pectrol fins and genital area.How-ever, dolphins lack an olfactory nerve and lobes and thus are believed to have no sense of smell. They do have a sense of taste and show preferences for certain kinds of fish. since dolphins spend most of their time below the surface, tasting the water could function like smelling, in that substances in the water can signal the presence of objects that are not in the dolphin's mouth.
Dolphins also display culture, something long believed to be unique to humans[and possibly other primate species]. In may 2005, a discovery in Australia found Indo-Pacific Bottlenose Dolphin[TURSIOPS ADUNCUS] teaching their young to use tools.They cover their snouts with sponges to protect them while foraging. This knowledge is mostly transferred by mothers to daughters, unlike simian primates, where knowledge is generally passed on to both SEXES. Using sponges as mouth protection is a learned beahvior . Another learned behavior was discovered among river dolphins in BRAZIL, where some male dolphins use weeds and sticks as part of a sexual display.
Dolphins engage in acts of aggression towards each other.The older a male dolphin is, the more likely his body is to be covered with bite scars. Male dolphins engage in such acts of aggression apparently for the same reasons as humans: disputes between companions and competition for females. Acts of aggression can become so intense that targeted dolphins sometimes go into exile as a result of losing a fight .........................
