Dolphins are conscious breathers not involuntary breathers; because of this, dolphins do not ever fully fall asleep, not the way that humans do. If the animals did fully fall asleep, they would drown. The dolphins shut down half the brain at a time and keep one eye open to look for predators while also staying alert enough to take a breath when needed.

Cetaceans are divided into three suborders: Archaeoceti (extinct whales), Odontoceti (toothed whales), and Mysticeti (baleen whales).

Archaeological evidence supports the theory that whales and dolphins evolved from terrestrial animals living over 50 million years ago.

The species have changed much over the centuries and have remained reasonably unchanged over the last 11 million years.

The species break down is as follows:
Mysticetes: four families of baleen whales.
(BALAENIDAE) - The bowhead, Northern Right Whale, and Southern Right Whale.
(Neobalaenidae) - The Pygmy Right Whale.
(Eschrichtiidae) - The Gray Whale.
(Balaenopteridae) - The Fin Whale, Bryde's Whale, Sei Whale, Blue Whale, Humpback Whale, and Minke Whale.

ODONTOCETES: Nine families of toothed whales.

(Physteridae) _ The Sperm Whale, Dwarf Sperm Whale, and Pygmy
Sperm whale.
(Monodontidae) - The Narwhal, and Beluga Whale.
(Ziphiidae) _ Eighteen species which include the Bottlenose Whale, Cuvier's Beaked Whale, Baird's Beaked Whale,
Strap-toothed Whale, and Sowerby's Beaked Whale.
(Delphinidae) - Thirty four species which include the Killer whale,
Pilot Whale, White-sided Dolphin, Common Dolphin, Bottlenose Dolphin, Spotted Dolphin, and Spinner Dolphin.
(Phocenidae) - Six species which include the Harbor Porpoise, and Dall's Porpoise.
(Platanistidae) - Five species of river dolphins.

The major differences between Mysticetes and Odontocetes are that Mysticetes have plates rooted in the roof of their mouth called baleen.
They have a series of hair like bristles that they use to help them feed. They work like filters. After the whales engulf large amounts of water, they forcibly eject the water through the baleen, filtering out creatures such as zooplankton, krill, and small schooling fish.

The odontocetes use their teeth to catch fish and squid.

The bottlenose dolphins, Tursiops truncatus, is the most common of all dolphins species. They grow to an average length of 9ft. and a weight of 600 lbs. They live between 35 to 45 years of age.

The species is divided into two categories: inshore and offshore. The offshore bottlenose are generally more robust than the inshore and live in very large pods that number fifty to several hundred. Offshore dolphins prefer the deep ocean waters of the continental shelf and beyond. The inshore dolphins choose shallow costal waters, bays, estuaries, and rivers.

The dolphins body is streamlined to reduce drag in the water. It has a strong muscular tail fluke for propulsion. External ears are lacking and genitalia are all tucked neatly away within the body only visible by slits. The dorsal fin provides stability at high speeds and pectoral fins control the direction. The dolphins smooth skin nearly eliminates all friction underwater. The dolphins skin has a cluster of water-filled tubes which form a spongy layer that is 80% water. This layer can rise and fall to subtle differences in external pressure. At high speeds the dolphin's skin will appear to ripple. The dolphin is constantly shedding which could act as a type of lubricant between the dolphin and the water.

The dolphin breathes air through it's blowhole at the top of it's head. This allows for uninterrupted swimming while it is at the surface. The dolphin does not breath through it's mouth and there is no connection with the mouth to the blowhole. This would help to explain how the dolphin is able to eat under water. The dolphin has no vocal cords and all the sounds that the dolphin makes are made from the blowhole.

Bottlenose dolphins have 104 cone shaped teeth which they use to catch and hold fish. The dolphins do not chew their food, they swallow it down whole. The dolphins do not drink water. They get all the water that they need through the fish they eat. The dolphin has a three chambered stomach. A fore stomach, which stores the food, a primary stomach, which breaks down the food, and a pyloric stomach, which dissolves the food into nutrients the body can absorb.

Dolphins and whales do not have exceptionally large lugs. They just make good use of the lugs that they have. Dolphins breathe two to three times per minute on average but can hold their breath for periods upwards of ten minutes. Cetaceans blood holds much more oxygen then humans. When a dolphin dives, the heart rate decreases and the system slows down. The mygloban in the muscles and stored oxygen in the veins, keep the vital organs sustained.

During a dive, most of the oxygen is stored in the blood and muscle rather than the lungs or tissue. When the dolphin dives below 200ft., the tiny air sacs inside the dolphins lungs collapse, preventing further gas exchange, including the absorption of nitrogen. This may help to explain why dolphins to not suffer from the bends.

Dolphins give birth to live young. The gestation period is approximately 12 months. The mother will give birth to a single calf. Twins have been born but are very rare and one usually dies but usually dies.

The calf usually comes out tail first and labor can last 20 minutes to two hours.

Dolphin’s hearing is amazing and they are capable of hearing sounds up to seven times higher in frequency than humans. They can hear up to 150kHz verses our 20kHz. A tiny pin hole is all that is visible of their ear. They have a special area to process sounds lower than 20kHz called the acoustic window.

Dolphins have very good sight and can see as well under water as they can on the surface. Dolphins also see with an amazing bio sonar called echolocation. The dolphins have an oil filled gland, found at the top of their head, called the mellon. It works as a lens to focus and beam sound through the water in front of them. The sound is reflected, or echoed back to the dolphin. It enters the lower jaw and is then read by the brain. It gives the dolphin a three dimensional picture of the target or object that it encountered.

Dolphins experience a variety of emotions from obvious happiness to grief. They have very advanced social structures and many of the dolphins stay in the same pods for life. They work as a team and use joint efforts for much that they do.

The largest dolphin of the dolphin family, the orca, is known to remain in its birth family for its entire life. Even the males remain with their mothers to help hunt and raise the young. The orca, or killer whale is considered to be the most intelligent of all the dolphins showing very advanced behavior and deductive reasoning.

There are over 90 different species of dolphins and whales and we have much to learn about them before we can truly know them.

Science is only now really beginning to understand just how advanced these animals are and how much we have to learn from them. There are many benefits from being able to understand a creature that is so many millions of years old with a brain as evolved as the cetacean.

for a extensive species breakdown please check out the link below.
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