Home>>All Animals>>Mammal>>Cetacea

Cetacea

Cetacea is an order of mammals, including about 90 existing fish-like, naked-skinned aquatic mammals and their extinct early relatives, collectively known as whales or cetaceans. The larger ones are usually called whales, and the smaller ones are called dolphins. Most of them live in shallow seas, and a few live in fresh water.

I. Introduction to Cetacea

1. Defining Characteristics:

  • Cetaceans are fully aquatic mammals with streamlined, fusiform bodies.

  • Forelimbs are modified into flippers; hind limbs are absent externally.

  • They possess a thick layer of blubber for insulation, and most have a dorsal fin or ridge.

  • Breathing is through a blowhole (or pair of blowholes in baleen whales) located on top of the head.

  • Reproduction, birth, and nursing occur entirely in the water.

2. Diversity and Distribution:

  • About 90 extant species of cetaceans inhabit all the world’s oceans and some rivers.

  • They range from the enormous blue whale (the largest animal ever known) to small porpoises and dolphins.


II. Evolutionary History

1. Origins:

  • Cetaceans evolved from terrestrial ancestors during the Eocene epoch (around 50 million years ago). Early fossils like Pakicetus indicate that their ancestors were land-dwelling, wolf-sized mammals. Over millions of years, these ancestors adapted to increasingly aquatic lifestyles.

  • The discovery of transitional fossils (e.g., Ambulocetus, Rhodocetus) shows the gradual modification from land locomotion to aquatic propulsion using tail flukes and forelimbs as flippers.

2. Transition to Full Aquatic Life:

  • By the late Eocene, early cetaceans were fully aquatic. Two major lineages diverged: the baleen whales (Mysticeti) and the toothed whales (Odontoceti).

  • Molecular and morphological data confirm that cetaceans share a close common ancestor with even-toed ungulates (Artiodactyla), especially hippopotamuses. This discovery led to the combined grouping known as Cetartiodactyla.

3. Adaptive Radiations:

  • Mysticetes adapted filter-feeding apparatuses (baleen plates) to exploit large amounts of small prey (krill, zooplankton).

  • Odontocetes developed echolocation abilities to navigate and hunt in often murky underwater environments, feeding on fish, squid, and sometimes marine mammals.


III. Classification Overview of Cetacea

Cetacea is traditionally divided into two suborders:

  • Suborder Mysticeti (Baleen Whales): Characterized by baleen plates instead of teeth, used to filter small prey from the water. They generally have two blowholes.

  • Suborder Odontoceti (Toothed Whales): Possess teeth (in varying numbers and shapes) and echolocation abilities. They have a single blowhole.

Below are the major families and some representative genera:

Suborder Mysticeti (Baleen Whales)

FamilyRepresentative Genera/SpeciesNotes
Balaenidae (Right and Bowhead Whales)Eubalaena (Right whales), Balaena (Bowhead whale)Large heads, long baleen plates, slow-moving filter feeders.
Balaenopteridae (Rorquals)Balaenoptera (Blue whale, Fin whale), Megaptera (Humpback whale)Streamlined, often pleated throats, gulp-feeding strategy.
Eschrichtiidae (Gray Whale)Eschrichtius (Gray whale)Bottom-feeder, short baleen, migratory along coastal routes.
Cetotheriidae (Pygmy Right Whale)Caperea (Pygmy right whale)Rare and enigmatic family; smallest baleen whale.

Suborder Odontoceti (Toothed Whales)

FamilyRepresentative Genera/SpeciesNotes
Physeteridae (Sperm Whales)Physeter (Sperm whale)Large head with spermaceti organ, deep divers feeding on squid.
Kogiidae (Pygmy Sperm Whales)Kogia (Pygmy and Dwarf sperm whales)Small, elusive whales with squid-based diet.
Ziphiidae (Beaked Whales)Ziphius (Cuvier's beaked whale), Mesoplodon (various species)Deep-diving, elusive, many species poorly known.
Monodontidae (Narwhal, Beluga)Monodon (Narwhal), Delphinapterus (Beluga)Arctic whales with unique features (tusk in narwhal, white beluga).
Phocoenidae (Porpoises)Phocoena (Harbor porpoise), Neophocaena (Finless porpoise)Small, robust, lacking a prominent beak, spade-shaped teeth.
Delphinidae (Dolphins)Tursiops (Bottlenose dolphin), Orcinus (Killer whale), Delphinus (Common dolphin)Highly diverse, social, and intelligent; largest Odontoceti family.
Iniidae (New World River Dolphins)Inia (Amazon river dolphin)Freshwater habitats in South America, long beaks, poor vision.
Pontoporiidae (La Plata Dolphin)Pontoporia (La Plata dolphin)Coastal and estuarine waters of eastern South America.
Platanistidae (South Asian River Dolphins)Platanista (Ganges and Indus river dolphins)Nearly blind, rely on echolocation in muddy river waters.

(Additional notes: The family Lipotidae, representing the Yangtze River dolphin (Lipotes vexillifer), is functionally extinct. Classification may vary slightly as some taxonomists treat river dolphins differently.)


IV. Summary

Cetaceans represent a remarkable evolutionary journey from land to water. Their extensive adaptive radiation has produced giants like the blue whale as well as highly social and intelligent dolphins and elusive deep-diving beaked whales. Modern molecular studies have situated cetaceans within the order Cetartiodactyla, reaffirming their close kinship with terrestrial ungulates such as hippos. Yet, historically and for the sake of clarity, Cetacea remains a well-recognized grouping for whales, dolphins, and porpoises, illustrating one of the most extraordinary transitions in mammalian evolution.

Carnivora Primates Rodents Chiroptera Eulipotyphla Ungulata Cetacea Lagoiformes Pholidota Proboscidea Monotremata
Physeter macrocephalus

Physeter macrocephalus

Physeter macrocephalus,Sperm Whale, Cachelot, Pot Whale, Spermacet Whale ,Cachalot , Ballena Esperma, Cachalote, Giant Sperm Whale, Kacherat Whale

Cetacea LC

Features:The sperm whale has the largest brain in the animal kingdom, and its intestinal secretion is the famous "ambergris"

Sperm Whale, with no subspecies, has the largest brain in the animal kingdom.Sperm whales like to live in groups, often with a few male whales and a large group of female whales and calves forming a large group of more than dozens, or even two or three hundred. They migrate north and south every yea...

Neophocaena phocaenoides

Neophocaena phocaenoides

Neophocaena phocaenoides,Indo-Pacific Finless Porpoise,Delphinus phocaenoides G. Cuvier,, black finless porpoise, Indo-Pacific right porpoise

Cetacea LC

Features:Also known as the broad-backed finless porpoise

The Indo-Pacific Finless Porpoise has no subspecies.The Indo-Pacific Finless Porpoise is a relatively shy and elusive animal. They do not form large groups. They like to move alone or in pairs, and usually do not form groups of more than 4-5. Most commonly seen in small groups including females and/...

Neophocaena sunameri

Neophocaena sunameri

Neophocaena sunameri,Narrow-ridged Finless Porpoise,Sand Mingli finless porpoise, narrow-ridged finless porpoise East Asian subspecies, finless porpoise East Asian subspecies, sea finless porpoise

Cetacea LC

Features:The smallest whale in the world is of course also the smallest toothed whale

The East Asian finless porpoise, also known as the Narrow-ridged Finless Porpoise, is the smallest cetacean and is often mistaken for the Yangtze finless porpoise. The height of its back and the number of tubercles are the main features that distinguish it from the Yangtze finless porpoise and the I...

Neophocaena asiaeorientalis

Neophocaena asiaeorientalis

Neophocaena asiaeorientalis,Yangtze Finless Porpoise,Narrow-ridged Finless Porpoise, Finless Porpoise,Neophocaena asiaeorientalis asiaeorientalis,Yangtze River Porpoise, Narrow-ridged Porpoise Yangtze

Cetacea LC

Features:The last remaining cetaceans in the Yangtze River

The Yangtze Finless Porpoise was once considered a subspecies of the narrow-ridged porpoise together with the East Asian finless porpoise. It was recognized as an independent species in 2018, which increased the number of cetacean species from 89 to 90. This also marks the addition of another endemi...

Globicephala macrorhynchus

Globicephala macrorhynchus

Globicephala macrorhynchus,short-finned pilot whale,Great nosed pilot whale, Great nosed pilot whale

Cetacea LC

Features:As the name suggests, the short-finned pilot whale has shorter flippers with rounded edges.

Short-finned pilot whale is a warm-water oceanic species.Short-finned pilot whales are most easily confused with other small black fish, such as false killer whales, followed by melon-headed whales and small killer whales. The dorsal fin is the best distinguishing feature.Short-finned pilot whales l...

Feresa attenuata

Feresa attenuata

Feresa attenuata,Pygmy Killer Whale, Orque pygmée,Orca Pigmeo,Delphinus intermedius,Small killer whale, small orca, small killer whale

Cetacea LC

Features:Related to killer whales

The pygmy killer whale is also known as the pygmy killer whale. It is an animal of the genus Pygmy Killer Whale in the family Delphinidae, with no subspecies. The "attentuata" in the scientific name means "wedge" in Latin, referring to the shape of its body gradually becoming thi...

Pseudorca crassidens

Pseudorca crassidens

Pseudorca crassidens,False Killer Whale, Faux-orque,Orca Falsa,Phocaena crassidens Owen,Black whale, false killer whale, false pilot whale, false killer whale

Cetacea LC

Features:Similar to killer whales, but smaller in size and all black

False killer whale is the only species in the genus False killer whale of the Dolphin family, and ranks third in size among the Dolphins.False killer whales are fast and active swimmers. When they float, they often lift their entire head and most of their body out of the water; sometimes even their...

Orcinus orca

Orcinus orca

Orcinus orca,Killer Whale, Orca,Epaulard, Orque, Espadarte, Orca,Orca assassina, killer whale

Cetacea LC

Features:It is the top of the marine food chain.

Killer Whale is the largest species in the dolphin family, and there is no subspecies.Killer whales are highly social and have a complex social structure. They like to live in groups, ranging from small groups of 2-3 to large groups of 40-50. There are even reports of hundreds of individuals in a gr...

Peponocephala electra

Peponocephala electra

Peponocephala electra,Toothy melon-headed whale, melon-headed dolphin

Cetacea LC

Features:Actually, the melon-headed whale is a dolphin.

Melon-headed whale, also known as Melon-headed whale, has no subspecies. Its characteristics are similar to those of the genus Orca, but it has more teeth.Melon-headed whales are a highly social species. They often appear in groups of hundreds or even more than 1,000, and the whale groups also inclu...

Grampus griseus

Grampus griseus

Grampus griseus,Risso's dolphin,Tattoo dolphin, Richter's dolphin, patterned whale, Richter's dolphin

Cetacea LC

Features:It has unique features such as no beak, no teeth in the upper jaw, the front end of the lower jaw is flush with the front edge of the head, and the blowhole is located on the top of the head.

The gray dolphin is called Risso's dolphin in English, and has no subspecies.The gray dolphin has the habit of swimming in the ocean. Usually there are groups of 10 to dozens of heads, and there are also large groups of hundreds of heads, and sometimes mixed with other types of dolphins. Gray do...

Lagenodelphis hosei

Lagenodelphis hosei

Lagenodelphis hosei,Fraser's Dolphin,Hourglass dolphin, Freund's dolphin, Freund's dolphin

Cetacea LC

Features:Its appearance is similar to that of the blue-and-white dolphin and the long-beaked dolphin.

The Sarawak dolphin is called Fraser's Dolphin in foreign language, and there is no subspecies.The Sarawak dolphin is a tropical, offshore species, and it usually swims in groups of dozens to hundreds of individuals, and even in large groups of thousands of individuals. They often swim with spot...

Delphinus

Delphinus

Delphinus,common dolphin,Common dolphin

Cetacea LC

Features:There is a triangular light-colored area in the center of the dorsal fin, and a deep groove on the left and right of the maxillary palate.

Common dolphins are called common dolphins in English. There are two species (long-beaked common dolphins and short-beaked common dolphins), with a total of four subspecies.Common dolphins belong to the order Cetacea, the family Delphinidae, and the genus Delphinus in taxonomy. There are two species...

Delphinus capensis

Delphinus capensis

Delphinus capensis,Long-beaked common dolphin, Common Dolphin,Toothed dolphin, tropical dolphin, long-beaked dolphin

Cetacea LC

Features:The basic appearance is similar to that of the short-beaked dolphin.

Long-beaked common dolphin, with two subspecies, is a warm-water species.Long-beaked dolphins are social mammals. Sometimes more than 1,000 individuals form a large dolphin group, and a smaller dolphin group can also be composed of 10 to 30 closely related dolphins.At the surface, long-beaked dolphi...

Stenella clymene

Stenella clymene

Stenella clymene,Short-snouted Spinner Dolphin,Clementine's dolphin, helmeted dolphin, spotted dolphin

Cetacea LC

Features:A new species produced by long-term hybridization between the long-beaked spinner dolphin and the striped dolphin

Short-snouted Spinner Dolphin, with no subspecies, is a deep-water species in the ocean.Differences between similar species: The short-beaked spinner dolphin is thicker than the long-beaked (spinner) dolphin (Stenella longirostris), and its dorsal fin is less triangular; in addition, as its name sug...

Stenella coeruleoalba

Stenella coeruleoalba

Stenella coeruleoalba,Striped dolphin,Blue and white dolphin, blue and white dolphin, striped dolphin

Cetacea LC

Features:A dolphin with spray-marked hair that excels at mid-air tail turns

Striped dolphin, with no subspecies, is a common dolphin in the Pacific Ocean.Striped dolphin has the habit of living in the ocean. They often move in groups of dozens to hundreds, and there are also large groups of thousands of them; in the Western Pacific, the groups can be divided into: juvenile...

Stenella attenuata

Stenella attenuata

Stenella attenuata,Pantropical spotted dolphin,Tropical spotted dolphin, weak dolphin, white-beaked dolphin

Cetacea LC

Features:Spots on the skin that darken with age

Pantropical spotted dolphin, with two subspecies, may be the most common cetacean.Pantropical spotted dolphin is a social animal, swimming in groups of a few to thousands, with more members in offshore groups than in coastal groups. In Japanese waters, 2-year-old dolphins will join other dolphins un...

Steno bredanensis

Steno bredanensis

Steno bredanensis,Rough-toothed dolphin,Long-beaked dolphin, wrinkled-toothed dolphin

Cetacea LC

Features:There are vertical fine wrinkles or ridges on the tooth surface, which is the origin of the Chinese name "rough teeth"

Rough-toothed dolphin, a dolphin with special teeth.Rough-toothed dolphins usually form a "pod" (a term for groups of dolphins, seals or whales) of 10 to 30, and there are also "pods" of up to 160, which contain 8 smaller groups. Occasionally swims with pilot whales, bottlenose d...

Platanista gangetica gangetica

Platanista gangetica gangetica

Platanista gangetica gangetica,Ganges River Dolphin,White puffer fish, Goto puffer fish

Cetacea LC

Features:The dolphin was blinded by the muddy river water.

The Ganges River Dolphin is a nominative subspecies of the South Asian river dolphin.The Ganges River Dolphin looks like a crocodile. When breathing, it often floats to the surface at a certain angle, so it may be mistaken for a crocodile in some areas. The entire head and beak of the Ganges River d...

Lipotes vexillifer

Lipotes vexillifer

Lipotes vexillifer,Baiji, Yangtze River Dolphin,Baiji,zhú (ancient name), Baiji, Chinese finless porpoise, Baiji dolphin

Cetacea LC

Features:In ancient Chinese literature, the Baiji dolphin is often used as a symbol of beauty and kindness.

The scientific name of the Baiji dolphin is Lipotes vexillifer, and its foreign name is Baiji. There is no subspecies. "Ji" is pronounced as "jì", and the media often writes it as "baiji dolphin". It is a small freshwater whale unique to China.The Baiji dolphin diverge...

Megaptera novaeangliae

Megaptera novaeangliae

Megaptera novaeangliae,Humpback whale,Humpback whale, humpback whale, saw-armed whale, saw-armed whale

Cetacea LC

Features:Humpback whales have extraordinary navigation abilities and will not deviate more than 5 degrees from their migratory route.

Humpback whale is not the largest whale in the world, but it is also a well-deserved giant in the ocean.Humpback whales mostly move in pairs, are gentle in temperament, and have a strong attachment to their companions. Every year, they migrate regularly from north to south: in summer, they migrate t...

Balaenoptera physalus

Balaenoptera physalus

Balaenoptera physalus,Fin Whale,Finback whale, baleen whale, razorback whale, herring whale, fin whale

Cetacea LC

Features:The second largest animal in the world

Fin whales are one of the fastest whales, with a speed of up to 37 kilometers per hour, and a record high of 40 kilometers per hour. They are known as the "greyhound of the deep sea".Fin whales use their baleen to filter food and then swallow it. Their food includes small fish, squid and c...