Lungs and Heart

• Dolphins possess lungs proportionately smaller than those of humans but which utilize oxygen far more efficiently. Increased amounts of myoglobin in their blood allows for effective oxygen retention. Dolphins have developed the ability to quickly inhale oxygen through their blowhole as they break the water's surface, and they are able to exchange up to 90 percent of the air in their lungs each time they exhale. Bottlenose dolphins are able to remain submerged for as long as 10 minutes. Their muscles function without oxygen during these periods when they are holding their breath. Most of the dolphin's blood is shunted to essential organs, such as the brain, lungs and heart when the animal dives. The heart also slows down during these periods to further conserve oxygen.
  
  

Thermoregulation

• Dolphins deposit the majority of their fat into a blubber layer, insulating the animal from its cold marine environment, particularly when diving to depths exceeding 1,500 feet. The blubber layer also streamlines the dolphin's body and acts as an energy reserve. These extremely active animals have a complex circulatory system, allowing them to control the flow of blood to their extremities. Through a process termed vasodilation, blood in arteries travelling to the extremities warms the cold blood returning to the body core from the flippers.
  
  

Streamlined Bodies

• Dolphins lack fur and possess a streamlined body. Their smooth skin creates little drag and allows for effective movement in water. The appendages of dolphins are highly modified to offer maximum propulsion and further reduce drag.
  
  

Communication and Camouflage

• Dolphins communicate in the marine environment by using sounds and echolocation. Each individual dolphin uses its own signature whistle. This highly sophisticated method of communication assists dolphins in locating prey otherwise difficult to see in murky waters. Dolphins rely on counter shading for camouflage. It conceals the animal while hunting and from predators. The dolphin's dark back blends into the water when viewed from above, while their light colored abdomen merges with the sunlit surface of the sea when viewed from below.