- Mammals breathe air with lungs.
- Mammals are "warm-blooded": they maintain a constant, high body temperature independent of their surroundings.
- As a rule, mammals bear live young. (Two primitive mammals are exceptions to this rule: the duckbilled platypus and the spiny anteater/echidna both lay eggs).
- Mammals nurse their young with milk.
- Mammals have hair, at least at some stage in their development. A whale's smooth skin is an adaptation for swimming. A newborn calf often has a few sparse hairs around the rostrum that are lost within the first days of life.
Order - Cetacea
Cetacea is a scientific order of large aquatic mammals that have forelimbs modified into flippers, a horizontally flattened tail, one or two nostrils at the top of the head for breathing, and no hind limbs. Cetaceans include all whales, dolphins, and porpoises.
The word "cetacean" is derived from the Greek word for whale, kētos.
Biochemical and genetic studies suggest that even-toed ungulates, especially hippopotamuses (Family Hippopotamidae), are cetaceans' closest living terrestrial relatives. (Sheep, cows, pigs, and giraffes are also examples of even-toed ungulates). These animals and whales probably share a common ancestor.
Some scientists suggest that since cetaceans genetically and morphologically fall within the artiodactyl clade, they should be included in the Order Cetartiodactyla with Cetacea as an unranked taxon.
Living cetaceans are further divided into two suborders: the Odontoceti (toothed whales) and the Mysticeti (baleen whales).
Suborder - Odontoceti
Odontoceti is a scientific suborder of whales characterized by having teeth and a single blowhole. The word "Odontoceti" comes from the Greek word for tooth, odontos.
Family - Delphinidae
Dolphins and their immediate kin are included in the scientific family Delphinidae. This family is represented by about 36 species, including bottlenose dolphins, pilot whales, and Commerson's dolphins.
Genus, Species - Cephalorhynchus Commersonii
Commerson's dolphins belong to the genus Cephalorhynchus, which includes three other dolphin species - Heaviside's, Hector's, and black (Chilean) dolphins.
- Cephalorhynchus means "head-beak" (kephalos = "head"; rhynchus = "beak/snout") and refers to the sloping forehead which merges directly into a short, blunt snout.
Other common names applied to this species include Jacobite, bridled dolphin, piebald dolphin, ground porpoise, and springer.
The Commerson's dolphin is named for French botanist, naturalist, and explorer Philibert Commerson who noted them on his travels to South America in 1767.
Fossil Record
The first whales appear in the fossil record about 50 million years ago. The ancestors of whales were ancient (now extinct) land mammals.
While the fossil record is poor in regard to modern cetaceans, most modern forms of odontocetes appear in the fossil record five to seven million years ago.
The oldest odontocete fossils are about 24 to 28 million years old.
