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Evolution of the Dolphin

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Canterbury School

on 15 February 2011

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Transcript of Evolution of the Dolphin

The Evoulution of the Dolphin Mary Layton Moffitt Fossil evidence from the early Eocene epoch, indicate that the early dolphins or Protocetidae were already aquatic 45-50 million years ago. But strangly, they don't resemblance to the dolphins and whales we know today. You can probably tell because they all look very alike All dolphins, whales, and porpoises are related. Protocetidae looked like this: Over time they may have become increasingly dependent of the ocean. Then passed through an amphibious stage before becoming fully committed to the ocean. It has been suggested by scientists that an early mammal called Mesonychidae roamed across the planes of Africa. These early mammals evolved into many ecological niches and ranged in size from cat to the size of a bear. They may also have be the antecedent of the modern horse. By comparing the fossil structures of the jaw and teeth of mesonychidae with the protocetidae, palaeontologists believe that these groups living on the coast began spending more time foraging for food in the swamps and ocean. We could imagine the transition between land and sea because it is just like the seals that we have today. Fossil dolphins can be traced through time by the changes in their teeth. Their body's thickened and their heads raised. Their vertebrae of the cetacean neck becamed fused. Because the dolphins evolutionary line diverged some 50 million years ago, their physical structure had time to develop independently from terrestrial mammals. The record also shows that once the early dolphins decided to become aquatic, it took a short amount of time for the bones of the hind legs to disappear altogether. For instance, the fossil record indicates that there was a stage when the animals were amphibious. The streamline of a dolphin's body was caused by living in water. But it also produced other modifications to the animal's apperence. Instead of the major blood supply to the brain running up the outside of the neck, as in land animals, it passes through an artery within the fused vertebrae. This insures a constant supply of blood when the dolphin dives to extreme depths in the ocean. The overall evoultion of the Dolphin looks like this: Their blow holes also moved up slowly to the back of their heads. T H E E N D
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