Quick facts

Whales, dolphins and porpoises are mammals and like all mammals, they breath air, are warm blooded, give birth to live young, lactate and  even have hair. (In the womb dolphins have a few whiskers around their snout and jaw bone, but this falls off and disappears entirely within a short amount of time). But unlike most other mammals, they do not have thick coats of hair to keep them warm, instead they have a layer of insulating fat, known as blubber which can be as thick as 50cm (20in).
(for more information on anatomy go to the anatomy page). 

Whales, dolphins and porpoises are known collectively as cetaceans from the Latin cetus (meaning large see animal) and the Greek ketos (meaning sea monster).
(For more information on Cetacea order go to Cetacea order page)

There are over 96* species of cetaceans that inhabit the world's oceans, lakes and rivers according to the World register of Marine Species*, but it is likely that more will be discovered and classified as new species in the future.
*[WoRMS Editorial Board (2023). World Register of Marine Species. Available from https://www.marinespecies.org at VLIZ. Accessed 2023-01-13. doi:10.14284/170 ]
(For more information on Cetacea order go to Cetacea order page)

They come in a variety of shapes and sizes, ranging from tiny dolphins just over 1m (39in) for the long-beaked common dolphin to the big Blue Whale, which is typically 25m (82ft) and is one of the largest animals to have lived on the Earth.
(For more information visit the Delphinidae family page)

They live in all the oceans, and many rivers of the world, from the warm waters of the Equator to the cold waters of the poles.
(For more information visit the location page)

Cetaceans eat a variety of food. Larger whales feed on shoals of fish or shrimp like creature such as krill. Whereas dolphins and porpoises tend to catch individual fish or squid. Other less common prey includes; octopus, molluscs, polychaete worms, crabs and turtles.
(For more information visit the Delphinidae family page)

To breathe when they are asleep, female dolphins lie on the water's surface with their blowholes exposed to the air; males sleep just below the surface and rise to breathe periodically as a reflex action.

Lifespan varies from around 20 years in the smaller dolphin species to 80 years or more for larger dolphins such as orcas and the bowhead whale  lives for an average of 100-200 years.
(For more information visit the Delphinidae family page)

The largest dolphin is the killer whale which can grow to  9.8m (32ft 2in) .
(For more information visit the Delphinidae family page)

The heaviest dolphin is the killer whale weighing upto 4 tonnes (8,818 pounds).
(For more information visit the Delphinidae family page)

Dolphins can stay submerged for up to 15 minutes.

Dolphin clicks are short pulses of 300 sounds per second.
(For more information visit the communication page)

Dolphins can dive to 300m (1000ft).
(For more information visit the Dolphins at Sea page)

Dolphins can swim sustained speeds of 32kph (20mph) with burst speeds of over 40kph (25mph).
(For more information visit the Dolphins at Sea page)

5 species of dolphin can live in fresh water, they are usually named after the river they swim in, such as the Amazon or the Ganges.
(For more information visit the Delphinidae family page)

The closest relative of cetaceans is the hippopotamus.