Dolphins are aquatic mammals of the infraorder Cetacea that constitutes five families, including oceanic dolphins, the Indian river dolphins, brackish dolphins, the New World river dolphins, and the extinct Chinese river dolphins. Research has shown that the ancestors of today’s dolphins were land-dwelling mammals, which became fully aquatic approximately 39-44 million years ago.
There are about 40 species of dolphins living today, divided into four extant families, including Platanistidae, Delphinidae, Iniidae, and Pontoporiidae. Some of the commonly found dolphin species are listed below:
Size: Dolphin species exhibit various sizes, ranging from the smallest Maui’s dolphin with a length of 5.6 ft (1.7 m) to the largest killer whales or orcas, measuring 31 ft (9.5 m). Several species like the long-beaked common dolphins display sexual dimorphism, with the males being more robust and longer than females.
Weight: The weight of dolphins varies depending on the species, with the Maui’s dolphin weighing 50 kg (110 lb) and killer whales having a weight of 10 tons (22,046 lb).
Color: They can have diverse color combinations. The Amazon river dolphin, for example, is grayish-pink or bright pink, while the killer whale and Commerson’s dolphins have a mix of black and white. Common dolphins come with a shade of dark gray and white.
Body: Dolphins have streamlined bodies, along with non-flexible necks, modified flippers, a tail fin, non-existent ear flaps, and bulbous heads.
Teeth: Unlike porpoises, dolphins possess conical teeth for catching quick-moving prey, including fish, squid, and seal. The number of teeth varies widely across species, with the orcas carrying 40-56 teeth, bottlenose dolphins having 72-116 teeth, and the common dolphins possessing 188-268 teeth.
Genitals: The reproductive organs occur inside their bodies, with the genital slits being located on the side of their belly. Males possess two genital slits, while the females have one.
Dolphins are widely distributed and found in all of the world’s oceans and some rivers. Although these aquatic mammals can inhabit the cold sub-Antarctic and Antarctic waters, most species prefer living in warm tropical areas.
Their habitat varies depending on food accessibility and environmental factors. While most of them are found in saltwater, some species of dolphins thrive in freshwater. Dolphins are usually seen in bays, creeks, rivers, inlets, shallow waters along the coast, and at great depths in oceans.
In captivity, the average lifespan of dolphins is only about 20-25 years, although there have been instances of killer whales living more than 30 years with two orcas, Lolita and Corky II, surviving up to their mid-40s. Wild dolphins have higher life expectancies, with the females living roughly 45 years on average, and sometimes up to 75-80 years. The males live for 31 years on average but can survive up to 55-60 years.
Dolphins typically feed on fish and squid, although the orcas and false killer whales also eat other sea mammals, such as dugongs and seals. Occasionally, orcas also hunt whales bigger than themselves.
Dolphins are polygynous, meaning the males mate with more than one female every year, while the females mate every 2-3 years. Copulation is generally brief, occurring belly to belly, often happening quite a few times within a short interval. The gestation period varies among dolphin species, ranging from 11-12 months in the tucuxis to roughly 17 months in the orcas. They typically give birth to one offspring in the spring or summer months, with the calf born tail first. Young dolphins usually become sexually active before reaching sexual maturity, which occurs at about 8-13 years of age.
Several organizations, such as the Hong Kong Dolphin Conservation Society (HKDCS) and the Whale and Dolphin Conservation (WDC), have been set up for their protection and welfare. The Mote Marine Laboratory, a Florida-based research organization, work on rescue and rehabilitation of wounded, sick, or orphaned dolphins. Countries like India have declared it as the national aquatic animal to save the Ganges river dolphin from extinction. The Vikramshila Dolphin Sanctuary has been established for their protection.
1. Are orcas dolphins?
Yes. Orcas are the largest dolphin species.
2. How do dolphins sleep?
Dolphins usually sleep with one of their brain hemispheres in a deep sleep at a particular moment, remaining conscious enough to breathe and be wary of the presence of predators or other threats. Captive dolphins enter a state of deep sleep with both eyes closed, automatic respiration, and no response to a mild stimulus.
3. How smart are dolphins?
Scientists have shown that dolphins have a high level of intelligence, demonstrating self-awareness, empathy, innovation, problem-solving ability, playfulness, teaching skills, grief, and joy. They are also known for their fantastic mimicry skills and quick learning ability.
4. Is a dolphin a fish?
No
5. Do dolphins have hair?
Baby dolphins have whiskers on their snout, but they lose them soon after birth.
6. Are dolphins endangered?
Some dolphin species, such as the Indus river dolphin, Ganges river dolphin, and Hector’s dolphin, are endangered.
7. How fast can a dolphin swim?
These aquatic mammals are fast swimmers. The orcas, for example, can swim with a top speed of 55.5 kph (34.5 mph).
8. What is a group of dolphins called?
A pod or school
9. How long can dolphins hold their breath?
On average, dolphins can remain submerged, holding their breath for 8-10 minutes. However, individuals have been observed to stay underwater for approximately 15 minutes.
10. What is a baby dolphin called?
A calf or pup
