Dolphin Characteristics, History, Taxonomy

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Mostly oceanic dolphins, with few freshwater ones, from Pinterest

Dolphins are sea mammals that arguably have the closest spiritual, intellectual and social link to humans of all sea creatures. Many people have said if they could come back as an animal they would choose to be a dolphin. Like otters, dolphins are regarded as intelligent and fun loving animals. In some cases this is a true, but they can also be aggressive and unpredictable and their habits and behavior are far from understood. [Sources: Jack MacClintock, Discover, March 2000; Kenneth Norris, National Geographic, September 1992 ; Edward J. Linehan, National Geographic, April 1979; Robert Leslie Conley, National Geographic, September 1966]

Like every mammal, dolphins are warm blooded. Unlike fish, who breathe through gills, dolphins breathe air using lungs. Dolphins must make frequent trips to the surface of the water to catch a breath. The blowhole on top of a dolphin's head acts as a "nose," making it easy for the dolphin to surface for air. Other characteristics of dolphins that make them mammals rather than fish are that they give birth to live young rather than laying eggs and they feed their young with milk. Also, like all mammals, dolphins even have a tiny amount of hair, right around the blowhole, which is a little different than the scales of a fish. Whales and porpoises are also mammals. There are 75 species of dolphins, whales, and porpoises living in the ocean. They are the only mammals, other than manatees, that spend their entire lives in the water.

Dolphins are not fish though there are fish also confusingly called dolphins. These days the fish are often call mahi mahi, their Hawaiian name, perhaps to avoid confusion. How did the dolphin name get attached to these fish. No one seems to know for sure. The word "dolphin" originally meant "womb", which aptly applies to female dolphins who have wombs and give birth to live young, but not the fish. One theory posited by BlueWater magazine is that underwater mammalian dolphins and dolphin fish make similar high-pitched noises to communicate. Maybe dolphin got their because this dolphin-like trait. [Source: Sciencing]

There are 37 species of dolphins (32 sea-going species and 3 river species). There are six species of porpoise. Dolphins inhabit all of the world's oceans. Some species are found in all of the world's seas. Others such as Pacific white-sided dolphins are are limited to one hemisphere or ocean. Still others have highly restricted ranges. For example, vaquitas (Phocoena sinus) only occur in the northern part of the Gulf of California. [Source: Eric J. Ellis and Allison Poor, Animal Diversity Web (ADW)]

Dolphins have lived to be 55 in captivity and are believed to live around the age of 30 in the wild. The distinct dolphin "smile" is a manifestation of the natural curve of the animal’s jawline not a friendly disposition. It is the result of a flared jawbone, which serves as an ultra-sensitive ear.

Dolphins have few natural predators other than orcas (killer whales) and sometimes sharks. They rely on their speed and agility to escape predators. Humans prey on whales throughout the world. Killer whales have been observed attacking dolphins. Large sharks are known to feed on porpoises and dolphins.

Websites and Resources: Britain-based Whale and Dolphin Conservation Society ; Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Fishbase; Encyclopedia of Life; Smithsonian Oceans Portal ; Monterey Bay Aquarium ; MarineBio

Cetacea: Dolphins, Porpoises and Whales

20110307-NOAA dolphins common _100.jpg Whales, porpoises and dolphins are known to scientists as cetaceans. There are at least 93 cetacean species. The skin of these creatures tends to be rubbery and smooth. The term Cetacea come from the Greek word ketos, which means “large sea creature”.

The order Cetacea comprises two extant sub-orders and one extinct sub-order. The extant sub-orders are Mysticeti (baleen whales) and Odontoceti (toothed whales). Both baleen whale and toothed whales are thought to be descendants of archaeocetes (Archaeoceti, ancient whales), an extinct sub-order. [Source: Eric J. Ellis and Allison Poor, Animal Diversity Web (ADW) /=]

There are at least 93 living species of cetaceans, with 46 genera in 14 families. New species are still being discovered. Of the two extant suborders, Odontoceti is larger and more diverse, with at least 70 species, 40 genera, and 10 families. Cetaceans, along with bats, are considered some of the most derived mammals on the planet. They evolved from terrestrial animals to an entirely aquatic life form that is completely separated from the land in all aspects of biology. Cetaceans live, breed, rest, and carry out all of their life functions in the water.

Cetaceans are exclusively aquatic. Most are species are marine, inhabiting coastal areas as well as the open ocean. A few species such as freshwater dolphins inhabit freshwater rivers. Others live in the brackish waters of estuaries. Almost all whales and dolphins have a thick layer of blubber. In species that live polar regions, the blubber can be as thick as 28 centimeters (almost a foot). In addition to providing warmth, this blubber help with buoyancy, offers some protection from predators, provides energy and nutrition during times when food is scarce. Calves are born with only a thin layer of blubber, but some species compensate for this with thick lanugos (soft, fine hair covering that cover a fetus while inside the uterus and after birth).


Odontoceti (also called odontocetes, toothed whales) are a parvorder of cetaceans that includes dolphins, porpoises, and whales possessing teeth, such as beaked whales and sperm whales. There are 73 described species. They include dolphins, porpoises, pilot whales, bottlenose whales and killer whales. Toothed whales such as killer whales and sperm whales are more similar to dolphins than baleen whales such as blue whales and humpbacks.

Evolution of dolphins
Odontoceti first emerged during Early Oligocene Period (33 million to 23.9 million years ago). They and baleen whales (Mysticeti), which have baleen instead of teeth, are thought to have diverged around 34 million years ago. Toothed whales include sperm whales, narwhals, belugas, Baird's beaked whales, pilot whales, killer whales, bottlenose whales and dolphins and porpoises. Toothed whales range in size from the 1.4 meters (4.6 feet) and 54 kilograms (119 pounds) vaquita to the 20 meters (66 feet) and 55 t (61-short-ton) sperm whale.

Odontocetes have torpedo-shaped bodies with inflexible necks, limbs modified into flippers, nonexistent external ear flaps, a large tail fin, skulls with small eye orbits and eyes on the sides of their heads . With the exception of sperm whales, they have bulbous heads. Many have long beaks. Odontocetes also have conical teeth designed for catching fish or squid. They have well-developed hearing, that is well adapted for both air and water, so much so that some can survive even if they are blind. Some species are well adapted for diving to great depths. Almost all have a layer of fat, or blubber, under the skin to keep warm in the cold water, with the exception of river dolphins.

Odontoceti teeth are comprised of cementum cells overlying dentine cells. Cementum is calcified or mineralized tissue covering teeth. Unlike human teeth, whose exposed parts outside the gum are mostly enamel, the exposed parts of toothed whale teeth are mostly cementum. The teeth differ considerably among the species. Some dolphins have more than 100 teeth in their jaws. At the other extreme are narwhals have a single long tusk and the almost toothless beaked whales with tusk-like teeth only in males. Not all species are believed to use their teeth for feeding. For instance, the sperm whale likely uses its teeth for aggression and showmanship.

Odontoceti have also evolved the ability to store large amounts of wax esters in their adipose tissue, an adaption that allows them to make deep dives. Species that have the highest amounts of wax esters in their blubber are also the species that can dive the deepest and for the longest amount of time.

Dolphin Evolution

Dolphins like whales evolved from a hoofed land mammal that took the seas 50 million years ago. Their ancestors hooves changed into fins. The evolution of cetaceans is thought to have begun in India and Pakistan from even-toed ungulates 55 million to 50 million years ago and took place over a period of at least 15 million years. During that time there was a common ancestor of whales and dolphins. Thus there is not evidence suggesting otherwise. [Source: Wikipedia]

Dolphins are part of the greater superorder "Cetartiodactyla" which split into the two major orders: "Artiodactyla" which consists of the ruminants, peccaries, pigs, hippos, llamas, and camels; and "Cetacea" which consists of porpoises, whales, and dolphins. It is estimated that order "Cetacea" diverged from the Artiodactylates in the early Eocene period 55.8 to 33.9 million years ago). After their divergence from "Artiodactyla" the Cetaceans split into two main suborders the "Toothed whales" (Odontoceti) and baleen whales ("Mysticetes") around 33.8 million years ago in the mid Eocene period. Within the suborder "Toothed whales" all modern dolphins are grouped under family "Delphinidae" which was estimated to first have appeared during the Early Miocene (23 million to 16 million years ago). [Source: Abigail Ross, Animal Diversity Web (ADW)]

The ancestors of dolphins that lived around 34 million years ago were large creatures with wolflike teeth. The first oceanic dolphins such as kentriodonts, evolved in the late Oligocene (33.9 million to 23 million years ago) and diversified greatly during the mid-Miocene (23 million –5.33 million years ago). The first fossil cetaceans near shallow seas (where porpoises inhabit) were found around the North Pacific. Species like Semirostrum were found along California (in what were then estuaries). These animals spread to the European coasts and Southern Hemisphere much later, during the Pliocene (5.4 - 2.4 million years ago).

Dolphins display convergent evolution with fish and aquatic reptiles.

Adam Wu, an evolutionary neurosurgeon, posted in in 2017: The relationship between dolphins and whales is akin to that between humans and great apes. Dolphins ARE whales, in the same sense that humans ARE great apes. Dolphins do not share a single common ancestor with all other whales, but many, just as humans do with the living great apes. The dolphins are one group among the toothed whales, in which their closest relatives are (probably) the porpoises. Thus dolphins share a common ancestor with porpoises, an earlier common ancestor with the other toothed whales, and an even earlier common ancestor with the baleen whales. From that point onwards, all earlier dolphin ancestors are identical to (and thus shared with) the ancestors of the rest of the living modern whales.

Dolphins and Whales Separately Evolved Similar Features

According to a study published in July 2020 in Current Biology a 24-million-year-old fossil of a giant tusked dolphin lacks several features common to modern dolphins and baleen whales, meaning that the common ancestor of dolphins and whales lacked these features, which in turn means the same adaptations for swimming must have evolved independently in both lineages. “We were surprised to find so many archaic features in an extinct dolphin,” says Robert Boessenecker at the College of Charleston in South Carolina. [Source: Michael Le Page, New Scientist, July 9, 2020]

New Scientists reported: Ankylorhiza tiedemani was one of the top predators in the sea from around 30 to 23 million years ago. The 5-metre-long dolphin would have looked much like a bottlenose dolphin, says Boessenecker, apart from its front teeth. These stick straight out and may have been used for ramming prey. Boessenecker’s team has been studying an A. tiedemani fossil found in the 1990s. “No one had found such a complete skeleton before,” he says. It revealed an unexpected lack of modern features.

Compared to ancient ancestors all modern whales and dolphins have extra vertebrae in their tails, giving them more flexibility and swimming power, and a very narrow base to the tail, just before the tail flukes. The “upper arm” bone in their pectoral flippers is very short relative to the other bones, and they have two or three extra finger bones. This helps make the flippers larger and stiffer, improving manoeuvreability.

It has been assumed that these features all evolved before the ancestors of baleen whales split from the ancestors of echolocating dolphins around 35 million years ago, says Boessenecker, but the fossil shows these features are instead a result of convergent evolution. “All these features evolved at least twice,” he says. We don’t know what Ankylorhiza preyed on. But if it lived in pods it would have been able to eat just about anything it wanted, says Boessenecker – including the 13-metre-long predecessors of megalodon sharks that lived at this time.

Harbor porpoise

Difference Between Dolphins and Porpoises

Dolphins and porpoises differ in their faces, fins, and body shapes. Dolphins have longer noses, bigger mouths, more curved dorsal fins, and longer, leaner bodies than porpoises. Dolphins tend to have prominent, elongated “beaks” and cone-shaped teeth, while porpoises have smaller mouths and spade-shaped teeth. The dolphin’s hooked or curved dorsal fin (the one in the middle of the animal’s back) also differs from the porpoise’s triangular dorsal fin. Generally speaking, dolphin bodies are leaner, and porpoises’ are portly. [Source: NOAA]

Dolphins have a defined beak, a pronounced bulbous forehead and a more streamlined body while porpoises have spade a rounded head. They are also generally smaller than dolphins. Porpoise teeth are flat, like chisels, instead of round, like pegs. Dolphins and porpoises have many similarities, one of which is their extreme intelligence. Both have large, complex brains and a structure in their foreheads, called the melon, with which they generate sonar (sound waves) to navigate their underwater world. In addition, porpoises are relatively r-selected compared with dolphins: that is, they rear more young more quickly than dolphins.

Dolphins are by far more prevalent than porpoises. Most scientists agree that there are 32 dolphin species (plus five closely related species of river dolphin) and only six porpoise species. Dolphins are also more talkative than porpoises. Dolphins make whistling sounds through their blowholes to communicate with one another underwater. Scientists are pretty sure that porpoises do not do this, and some think this may be due to structural differences in the porpoise’s blowhole.

Dolphin Characteristics

Dolphins generally have streamlined, fusiform, torpedo- or spindle- shaped bodies, with a singular dorsal (back) fin, two pectoral fins (one each on either side of its body), and a tail with horizontal flukes. This body type helps the animals move quickly and easily through the water. Sexual dimorphism (differences between males and females) exists: Among some species females are larger than males. Among others males are larger. Male bottlenose dolphins are larger than female bottlenose dolphins. Ornamentation can be different. [Source: Abigail Ross, Animal Diversity Web (ADW) /=]

Coloration is often gray, bluish-gray or grey almost black on their dorsal side, and light grey or whitish shading on their ventral (belly) side. Some are pink or spotted or have mottled or streaked patterned. Most exhibit some countershading, tending to be lighter on the bottom than on the back, which is distinct near the head, with the two colors fading into each other near the tails. Countershading helps the dolphins blend in with water when view from above and blend in with the sky or ocean surface when viewed from below.

All cetaceans (whales and dolphins) share a number of common characteristics. They have paddle-shaped front limbs; a laterally flattened tail with horizontal flukes at the end; vestigial hind limbs (which are within the body wall); no external digits or claws; and vestigial ear pinnae (the outer part of the ear). They have a basically hairless body (some young have hair on their snouts); telescoped skull bones;; a thick subcutaneous blubber layer filled with fat and oil; external blowholes (nares) on the top of their head; lack of sweat glands; internal reproductive organs; three-chambered stomach; and an airway reinforced with cartilage to the alveoli. Cetaceans have diploid chromosome numbers of 42 to 44. [Source: Eric J. Ellis and Allison Poor, Animal Diversity Web (ADW) /=]

Dolphins and porpoises have no external genitals. All their sensory organs are recessed into slits so they can move through the water with less friction and drag. The fastest dolphins can swim at around 38 kilometers per hour (23 mph). Many dolphin characteristics are adaptations to reduce drag for fast swimming in an aquatic environment. Protuberances such as external ears or genitals would create turbulence, friction and drag. They have compressed vertebrae, which shortens the neck but increase speed

Dolphin anatomy

Dolphins and whales have hair and blubber — milky, white fat underneath a animal’s skin. Like whales, dolphins have a horizontal fluke rather than vertical tail fins like fish. Dolphins propel themselves forward by moving their fluke up and down. A subdermal sheath is attached to the dolphin’s muscles and skeleton. Dolphins are able to keep their skins clear of parasites that attach to whales through special features in their skins: nanometer-size ripples and ridges with a gel-like coating. Scientists are studying dolphin skin for clues on how to keep ships clear of barnacles and tubeworms. [Source: Robert Leslie Conley, National Geographic, September 1966]

The fins of different species of dolphin are adapted to how they move. Long, narrow fins are good for fast swimmers while broad, short ones have evolved among species that need to maneuver in small spaces and make tight turned. [Source: National Geographic]

Dolphin Anatomy and Metabolism

Dolphins and porpoises are endothermic (use their metabolism to generate heat and regulate body temperature independent of the temperatures around them) and homoiothermic (warm-blooded, having a constant body temperature, usually higher than the temperature of their surroundings)

Many dolphins have proportionately large brains. Some cetaceans are thought to be the most intelligent non-primate animals. Dolphins have several stomachs, like cows, which may be remnants from its terrestrial ancestors that lives tens of millions of years ago. Dolphins collect salt in their kidneys like camels.

Dolphin have a two-chambered stomach similar ones in terrestrial carnivores. Dolphins, porpoises and toothed whales generally grab their prey with their toothy jaws and swallow it whole and digest it in their multi-chambered stomachs. Toothed whales' large teeth that can slice and rip. They have throats large enough to swallow fish and squid, their main prey, or chunks of large fish or aquatic mammals. Many have scars perhaps from courtship battles between other whales.

Dolphins are found in many different climates, including regions where sea water is near freezing. Small cetaceans can cope with cold temperatures because they have high metabolic rates. Also, their flippers and flukes have a countercurrent heat exchange system, wherein heat from arterial blood warms venous blood as it returns to the heart. Both small and large cetaceans are insulated by their thick blubber layer. /=\

spinner dolphins

Dolphin Breathing

Breathing involves expelling stale air through a a single blowhole (many baleen whales have two) followed by inhaling fresh air into the lungs. Exhalations through the blowhole produce upward steamy spouts. Spout shapes differ among species, which serves as a means of identification. The spout only forms when warm air from the lungs meets cold air, thus does not form in warmer climates.

Dolphins have remarkably efficient lungs and circulatory systems, allowing them to dive for extended periods of time. Cetaceans use about 12 percent of the oxygen that they inhale, compared to 4 percent used by terrestrial mammals. They also have at least twice as many erythrocytes and myoglobin molecules in their blood, for efficient capture and transport of oxygen. When cetaceans dive, their heart rates slow by as much as 80 beats per minute, so their bodies use less oxygen than they would otherwise. [Source: Eric J. Ellis and Allison Poor, Animal Diversity Web (ADW) /=]

Dolphins blowholes are about the size of a quarter with inner valves and out outer valves to seal out water when the dolphin is under water. When they surface dolphins inhales four to ten liters of air in one second. They can blow bubbles from their blowholes. Bottlenose dolphins come to the surface an average of once every 28 seconds to breath. In aquariums they have been observed making rings and other shapes with bubbles and playing with them. [Source: Edward J. Linehan, National Geographic, April 1979]

Thanks to rapid gas exchange at the capillary level, double the amount of red blood cells, and about two to nine times the amount of myoglobin (a protien that supplies oxygen to cells) of land animals, dolphins are able to alternate between no breathing while deep diving and normal breathing while swimming along the surface. [Source: Jessica Jenkins, Animal Diversity Web (ADW)]

Dolphin Swimming and Jumping

Dolphins swim up to 100 miles a day, jump 15 feet straight up, and can reach speeds up to 20 mph for short bursts. Some boaters have claimed they have seen dolphins traveling over 40 mph. Scientists say that in these cases the dolphins were probably getting a boost from the boat's bow wave. [Source: Kenneth Norris, National Geographic, September 1992]

Whales, dolphins, and porpoises have two flippers on the front, and a tail fin. These flippers contain four digits. Although dolphins do not possess fully developed hind limbs, some possess discrete rudimentary appendages, which may contain feet and digits. [Source: Wikipedia]

Dolphins are fast swimmer. Their fused neck vertebrae in toothed whales increases stability when swimming at high speeds but decreases flexibility, rendering them incapable of turning their heads. When swimming, toothed whales rely on their tail fins to propel them through the water. Flipper movement is continuous. They swim by moving their tail fin and lower body up and down, propelling themselves through vertical movement, while their flippers are mainly used for steering. Some species log out of the water, which may allow them to travel faster. Most species have a dorsal fin.

Dolphins can reach high speeds because they flex back and forth like spring-loaded pogo sticks. As they lift their tail, blubber on the top side is compressed and stretched, storing energy for spring-loaded down stroke. As the muscles relax compressed blubber springs back and help push the tail down.

Dolphin Diving

Dolphins inhale before diving. They can stay underwater anywhere from a few seconds to over an hour at a time. Dolphins have been recorded diving up to depths of 520 meters (1,700 feet). Bottle nose dolphins can dive to a depth of around 150 meters (500 feet). Seals, whales and dolphins all relax when diving, allowing them to reduce oxygen consumption and dive deeper and stay submerged longer. The collapsible rib cage that dolphins have pushes all of the air out of their lungs which keeps them from getting the bends. [Source: Edward J. Linehan, National Geographic, April 1979]

Scientists have long wondered exactly how dolphins, whales and seals can stay under water so long. The secret seems to be that they float rather than swim downwards to conserve energy and do not use up oxygen unnecessarily. The stay as still as possible on the way down and use their energy to catch prey and swim back up. Whales, seals and dolphins all seem to use the same strategy. Scientists were able to observe his phenomena by strapping critter cam cameras on bottlenose dolphins, Wendell seals and even a blue whale.

Many toothed whales are adapted for diving to great depths, but many porpoises and dolphins are not. In addition to their streamlined bodies, they can slow their heart rate to conserve oxygen; blood is rerouted from tissue tolerant of water pressure to the heart and brain among other organs; haemoglobin and myoglobin store oxygen in body tissue; and they have twice the concentration of myoglobin than haemoglobin. Before going on long dives, many toothed whales exhibit a behaviour known as sounding; they stay close to the surface for a series of short, shallow dives while building their oxygen reserves, and then make a sounding dive.

Image Source: Wikimedia Commons, NOAA

Text Sources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated June 2023

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