Learn About Dolphin Anatomy

Internal
External
1 Internal Anatomy
Internal
Int An

Bottlenose dolphins have up to 104 cone-shaped teeth which they use to grab hold of their prey.  They eat a wide variety of fish, normally of a size they can swallow whole.  A strong sphincter muscle in the throat enables dolphins to swallow their food without ingesting too much seawater.  Rather than drink saltwater, they acquire most of their fluids from the fish they eat.  Dolphins are very efficient at metabolizing the fats and proteins in their food in order to extract fresh water and stay sufficiently hydrated.  

1 External Anatomy
External
10 Graph Ext

The dolphin’s external anatomy is well adapted to the aquatic environment.  The body is streamlined with obvious adaptations to reduce drag in the water.  The hind legs have given way to a fibrous tail fluke for propulsion.  External ears are lacking and genitalia have receded into the body cavity.  A fibrous dorsal fin provides stability at high speed and pectoral fins control the direction of travel.  The animal’s smooth skin nearly eliminates underwater friction.

The dolphin’s blowhole allows for uninterrupted swimming while breathing at the surface.  There is no connection between the dolphin’s mouth and airway (an obvious advantage for feeding underwater).  They also lack vocal cords and are incapable of producing sounds from the throat or mouth.  All of the sounds appear to originate from the region of the nasal plug and air sacs just beneath the blowhole.  Some sounds are produced by expelling air through the blowhole, but most seem to b generated internally without loss of air.

Kidney
Internal
12 Graph Kidney

To rid the body of any excess salt, dolphins rely on their relatively large kidneys.  These are divided into numerous lobules (reniculi), which considerably increase the surface area needed for elimination.  Dolphin urine normally has a high salt content.   

Stomach
Internal
8 Graph Stomach

The dolphin has a three-chambered stomach – a forestomach which stores the food, a fundic stomach where food is broken down, and a pyloric stomach where digestive enzymes from the liver and pancreas are introduced to dissolve food into nutrients the body can absorb.  Further absorption takes place in the small intestines.  Any remaining material that cannot be absorbed as nutrient passes through the large intestine and out through the rectum.

Respiration and Circulation
Internal
Resp And Circ

Dolphins have developed a remarkable combination of respiratory and circulatory modifications for diving.  Although dolphins may take a breath of air on the average of two to three per minute, they can hold their breath for periods in excess of 10 minutes.

In order for dolphins to be able to hold a breath so long, one would assume they have an enormous lung capacity.  However, while dolphin lungs are bigger, and hold a larger volume of air than ours, it is in the management of that air which gives them such a great advantage.  That advantage begins with a single breath.

Whereas land mammals exchange only 10-15% of the air in the lungs with each breath; dolphins exchange as much as 90%.  They also transport more oxygen across the lung membranes and into the bloodstream.  While we can remove only 5-6% of the available oxygen in our lungs, they can remove as much as 12%.

Red blood cells, together with a respiratory pigment called hemoglobin, transport oxygen throughout the body.  Dolphins have larger red blood cells and higher concentrations of hemoglobin than we do, which in turn increases the amount of oxygen their blood can carry.

Another pigment, found in the muscles, is called myoglobin and it helps unload oxygen from the bloodstream.  Myoglobin is also more abundant and more concentrated in the muscles of dolphins than in terrestrial mammals.

Skin
External
Skin

A microscopic cross section of a dolphin’s skin reveals a cluster of water-filled tubes forming a spongy layer that is 80% water and can rise and fall in response to subtle differences in external pressure.  At high speed, the skin surface will sometimes appear to “ripple”.  Cell formation occurs actively and constantly on the skin surface.  The continuous shedding may act as a kind of lubricant between the dolphin and the water.

Dorsal fin
External
Dee Dee Mosa Ritina Suku

Main purpose of the dorsal fin is that of a stabiliser, like the lee-board on a boat. The dorsal fin is made of connective tissue. It also contains some blood vessels and plays a role in thermoregulation.

Fluke
External
Tela Serena 8

The tail of the dolphin consists of 2 blades called the flukes. The tail flukes contain no bones, but are made of collagen-rich connective tissue. The tail flukes are horizontal. They are the main source of propulsion. When swimming the tail flukes are moved up and down, unlike a fish's tail, which moves from side to side. The tail flukes are connected to some groups of powerful muscles in the back and the belly of the dolphin. Bottlenose dolphins can reach speeds of up to 25 miles an hour.

Pectoral fins
External
Tela Serena 3

The flippers act as stabilizers and as rudders: they are used for steering and stopping while swimming. The flippers are also used to establish brief bodily contact in social interactions between dolphins. The pectoral fins have bones that resemble that of a hand with 5 digits. 

Eyes
External
Tela3

The eyes are located on the side of the head, close to the corners of the mouth. A tear duct is present in the forward corner of the eye. Dolphin tears are very viscous are secreted in large quantities. Their main function is probably protection and lubrication of the cornea. The tears contain slightly less salt than blood, which in turn contains less salt than the surrounding sea water. 

Ears
External
Mosa1

The small pinholes behind the eye are the dolphin's ear openings. 

Melon
External
Tela3

The bulbous forehead of the dolphin is called the melon. This melon sits in front of the skull and is connected to a system of air sacs. It plays a role in echolocation 

Blowhole
External
Tela3

The dolphin’s blowhole allows for uninterrupted swimming while breathing at the surface.  There is no connection between the dolphin’s mouth and airway (an obvious advantage for feeding underwater)