Altogether, the two suborders contain eighty-one known species, separated into thirteen different families. In each family are a number of species, each classified further into 'sub-families', or genera, of which there are 40.
Millions of years ago, they lived on land; their bodies were covered in hair, they had external ears, they walked on four legs, they bared live young.
Dolphins' ancestors once lived on land and looked like wolves, although they were more closely related to cows.
The cetacean returned to the sea - there were more food there, and more space than on land. Because of this increase in space, there was no natural limit to the cetacean's size (i.e. the amount of weight its legs could hold) since the water provided buoyancy. It had no longer any need for legs.
During this time, the cetacean lost the qualities that fitted it for land existence and gained new qualities for life at sea. Its hind limbs disappeared, its body became more tapered and streamlined - a form that enabled it to move swiftly through the water. For the same reason, most of its fur disappeared, reducing the resistance of the giant body to the water. A pair of flukes that acted like a propeller replaced the cetacean’s original tail.
As part of this streamlining process, the bones in the cetacean's front limbs fused together. In time, what had been the forelegs became a solid mass of bone that became fins for steering, although they still have a lands mammal’s finger like bones, blubber and tissue, making very effective flippers that balance the cetacean's tremendous bulk.
After the cetacean's hair disappeared, it needed some way of preserving their body heat. This came in the form of blubber, a thick layer of fat between the skin and the flesh that also acts as an emergency source of energy. In some cetaceans the layer of blubber can be more than a foot thick.
o Fossil evidence from the early Eocene epoch, indicate that the early dolphins or Protocetidae were already aquatic 45-50 million years ago. However they bore little resemblance to the dolphins and whales we know today.
dolpcomunication
There are many different kinds of dolphins, around forty species of dolphins, including some species we would commonly call whales, such as Orcas and pilot whales. Bottlenose dolphins (Tursiops truncatus) are one of the most wide-ranging species. They live along tropical and temperate coasts all around the world, like Brazil; there are 25 types of dolphins in Brazil. Other species of dolphins live in cold waters, such as the Atlantic white-sided dolphin that can be seen from the Gulf of St.Lawrence to the North Sea, and the hourglass dolphin that lives in the waters of the Antarctic
There are over 33 different species of dolphins, over 5 different species of river dolphins, and over 6 different species of porpoise.
Ocean Dolphins: Atlantic White-sided Dolphin, Atlantic Borneo White Dolphin, Bottlenose Dolphin, Borneo White Dolphin, Bouto Dolphin, Broad-beaked Dolphin, Cameroon Dolphin, Chinese White Dolphin, Clymene Dolphin, Commerson's Dolphin, Common Dolphin, Dusky Dolphin, Falkland Island Dolphin, Fraser's Dolphin, Heaviside's Dolphin, Hector's Dolphin, Hour-glass Dolphin, Long-snouted Spinner Dolphin, Northern Right Whale Dolphin, Pantropical Spotted Dolphin, Peale's Dolphin, Plumbeous Dolphin, Rio de Janeiro Dolphin, Risso's Dolphin, Rough Toothed Dolphin, Southern Right Whale Dolphin, Speckled Dolphin, Spinner Dolphin, Spotted Dolphin, Striped Dolphin, White- beaked Dolphin,White-bellied Dolphin, White-sided Dolphin.
River Dolphins: Amazon River Dolphin, Baiji Dolphin, Indus River Dolphin, Ganges River Dolphin and Guiana River Dolphin.
Porpoises: Black Porpoise, Black Finless Porpoise, Cochito, Dall's Porpoise, Finless Porpoise,
Harbor Porpoise, Spectacled Porpoise, True's Porpoise.
