- Mammals are characterized by the following features:
- 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 both lay eggs.)
- Mammals nurse their young with milk.
- Mammals have hair, at least at some stage in their development. Many baleen whales have sparse hairs on the snout, jaws, and chin.
- Cetacea is a scientific order of large aquatic mammals that have forelimbs modified into flippers, a horizontally flattened tail, a nostril 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.
- Living cetaceans are further divided into two suborders: the Odontoceti (toothed whales) and the Mysticeti (baleen whales).
- Mysticeti is a scientific suborder of whales that have plates of baleen in the upper jaw. The word "mysticete" may be derived from the Greek word for moustache, mystakos. It may refer to the hairy appearance of these whale's baleen plates. Baleen whales are sometimes referred to as the "great whales".
Mysticete Families, Genera, And Species
- Family Balaenopteridae (the rorqual whales).
Rorqual (from the Norwegian, rørhval) whales have extremely long, streamlined bodies with many longitudinal grooves along the skin of the throat. A rorqual whale has a small dorsal fin and short (compared with other baleen whales) baleen plates.
FAMILY BALAENOPTERIDAE: THE RORQUAL WHALES
Family Balaenidae (the right whales).
- minke whale (Balaenoptera acutorostrata)*
- Sei whale (Balaenoptera borealis)
- Bryd's whale (Balaenoptera edeni)
- blue whale (Balaenoptera musculus)**
- fin whale (Balaenoptera physalus)
- humpback whale (Megaptera novaeangliae)
* Some scientists identify three geographically isolated populations of minke whales that may be separate subspecies:
- Balaenoptera acutorostrata acutorostrata (North Atlantic)
- Balaenoptera acutorostrata bonarensis (southern hemisphere)
- Balaenoptera acutorostrata davidsonii (North Pacific)
** Some scientists identify three subspecies of blue whale:
- Balaenoptera musculus brevicauda (pygmy blue whale of subantarctic Indian Ocean and southeastern Atlantic Ocean)
- Balaenoptera musculus musculus (northern hemisphere)
- Balaenoptera musculus intermedia (southern hemisphere)
A right whale has a smooth throat and a disproportionately large head with very long baleen plates in a hugely arched jaw. With the exception of the pygmy right whale (Caperea marginata) whales in this family do not have dorsal fins. Right whales were so named by whalers who deemed them the "right" whales to hunt.
FAMILY BALAENIDAE: THE RIGHT WHALES
Family Eschrichtiidae (the gray whale).
- bowhead whale (Balaena mysticetus)
- pygmy right whale (Caperea marginata)
- northern right whale (Eubalaena glacialis)
- southern right whale (Eubalaena australis)
A gray whale has a few throat grooves, short baleen plates, and a small dorsal hump followed by a series of bumps. This family has one living member, the gray whale (Eschrichtius robustus).
Most scientists recognize three families of baleen whales. Some recognize a fourth family, Neobalaenidae, which includes only the pygmy right whale Caperea marginata. This whale has characteristics of both rorquals and right whales: its head is not as disproportionately large as that of other right whales; it has a small dorsal fin; and it has two rather indistinct grooves along the skin of its throat.
- gray whale (Eschrichtius robustus)
- Scientists believe that early whales arose about 55 to 65 million years ago from (now extinct) ancient land mammals that ventured into the sea. These ancestors of present-day whales had some adaptations for an aquatic life. Scientists agree that ancestors of both toothed and baleen whales probably had teeth.
- Fossils indicate that the earliest known baleen whales lived about 30 million years ago. By 25 million years ago, early members of the right whale family appeared. Members of the rorqual family appeared about 15 million years ago, including the modern genus Megaptera.
- Most modern forms of both odontocetes and mysticetes appear in the fossil record five to seven million years ago, but the fossil record is poor. The relationship between early whales and modern baleen whales is unclear.
- The modern genus Balaenoptera appeared about 5 to 10 million years ago.
- The modern genus Balaena appeared about 5 million years ago.
- The modern gray whale family, Eschrichtiidae, appeared 2 million years ago.