Not evaluated Cetaceans — whalesdolphins and porpoises — are placental marine mammals. All modern members of the infraorder are fully aquatic and live in the open ocean except a few species of dolphin which inhabit rivers and estuaries.
Locomotor adaptations The most noticeable adaptation of cetaceans to life in the water is their locomotive system.
Because cetaceans descended from mammals that moved their limbs in a vertical plane rather than in a horizontal plane, they use vertical strokes when they swim, instead of horizontal strokes like a crocodile or fish. Cetaceans evolved from four-legged quadruped terrestrial animals, for which limbs played a primary role in movements, into virtually limbless aquatic creatures living in an environment where the back muscles are more important.
Forelimbs are still present but are reduced to finlike flippers having shortened arm bones and no individual fingers.
The hind limbs are lost entirely; only vestigial elements sometimes remain internally. Pelvic remnants occur in all cetacea but the dwarf and pygmy sperm whales. Flippers help to steer, while the back muscles, which are very large, drive the tail to propel the animal. Cetaceans have developed horizontal flukes that increase the propulsion area driven by the back muscles.
Like fish, almost all cetaceans possess a dorsal fin that serves as a keel. The dorsal fin and flukes are composed of connective tissuenot bone. Other connective tissue, such as external ears, has been lost, and the male genitalia have moved internally.
Humpback whale Megaptera novaeangliae breaching. The blow is expelled forcibly and can be compared to a cough. Cetaceans use up to 80 percent of their lung volume in a single breath, in contrast to humans, who use only 20 percent. The blow is visible because of water condensation and mucous particles; blows of blue whales are frequently more than 6 metres 20 feet high.
When a terrestrial mammal loses consciousnessit breathes reflexively, but breathing is not a reflex in cetaceans. Thus, when a cetacean loses consciousness, it does not breathe and quickly dies.
For this reason, veterinarians had to perfect respirators before dolphins could be successfully anesthetized. Circulation and thermoregulation Cetaceans, like all mammals, have a four-chambered heart with paired ventricles and auricles. The pattern of circulation is similar to that of other mammals, with the exception of a series of well-developed reservoirs for oxygenated blood called the rete mirabilefor "marvelous network.
Cetacean evolution has countered this problem in three ways: The reduction of various appendages as mentioned above also facilitates locomotion in water. In whales, a layer of the skin dermis has evolved into a blanket of blubberwhich is extremely rich in fats and oils and therefore conducts heat poorly.
The oil yield of blubber from a blue whalefor example, was up to 50 tons. The most important mechanism in cetacean thermoregulation is the development of countercurrent blood exchange, an adaptation that allows the animal to either conserve or dissipate heat as needed.
If it returns by the peripheral route, the blood courses back to the heart through superficial veins, where it continues to lose heat and arrives at the heart cool. Such heat shedding is particularly important to large whales because of their enormous surface area-to-volume ratio.
If, however, the body temperature of the whale is already cool, the oxygen-depleted venous blood can instead return to the heart through vessels that are wrapped around arteries carrying warm blood to the periphery of the animal.
Along this route the venous blood is warmed by the arterial blood and arrives at the heart warm. The arterial blood, having transferred its heat into the venous blood rather than the environment, arrives precooled at the surface of the skin.
Feeding adaptations Before cetaceans evolved aquatic adaptationsthey had a fully differentiated set of teeth heterodont dentitionincluding incisors, canines, premolars, and molars.
As the animals became more adapted to aquatic locomotion and lost the ability to manipulate food with their forelimbs, they started grabbing their food and swallowing it whole. In toothed whales suborder Odontocetiheterodont dentition declined and was replaced with a homodont dentition in which every tooth is a simple cone.
The number of teeth varies among toothed whales, from two in the beaked whales family Ziphiidae [Hyperoodontidae in some classifications] to in the La Plata river dolphin Pontoporia blainvilleito allow efficient capture of prey. Baleen whales suborder Mysticetion the other hand, have lost all teeth in both jaws and instead have two rows of baleen plates in their upper jaws only.
Cetacean - Paleontology and classification: Cetaceans are distant descendants of a group of poorly defined mammals known as condylarths. There is debate as to whether the first cetaceans (archaeocetes) descended from an extinct group of large carnivores called mesonychids or from a group of hoofed herbivores (artiodactyls). The earliest archaeocetes were huge dolphinlike creatures 6 to Cetacean A whale, dolphin or porpoise. Cetaceans A group comprising all whales, dolphins and porpoises. Dorsal fin The unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans. Cetacea (/ s ɪ ˈ t eɪ ʃ ə /) is a widely distributed and diverse clade of aquatic mammals that today consists of whales, dolphins, and regardbouddhiste.comans are carnivorous and finned. Most species live in the sea, some in rivers. The name is derived from the Latin cetus "whale", itself from the Greek κῆτος kētos "huge fish".. There are around 89 extant species, which are divided.
This apparatus enables baleen whales to consume vast quantities of small prey in a single mouthful. Killer whale Orcinus orca. Miami Seaquarium In general, whales have relatively large mouths. The mouth of one adult bowheador Greenland right whale Balaena mysticetusmeasures five metres long and three metres wide and is the biggest oral cavity on record.
The stomach in cetaceans is composed of four compartments: The forestomach is actually a dilation of the esophagus and is lined with simple epithelium layers of flattened cells.
It acts merely as a holding chamber and therefore is not a true stomach.Healthy marine species like whales, sea turtles, coral, and salmon are important for maintaining balanced and thriving ocean ecosystems.
We work to prevent marine species populations from decline and extinction, protect them from human activities, and monitor activities that might impact them so they are around for future generations. Cetacean - Paleontology and classification: Cetaceans are distant descendants of a group of poorly defined mammals known as condylarths.
There is debate as to whether the first cetaceans (archaeocetes) descended from an extinct group of large carnivores called mesonychids or from a group of hoofed herbivores (artiodactyls). The earliest archaeocetes were huge dolphinlike creatures 6 to Cetacean: Cetacean, any member of an entirely aquatic group of mammals commonly known as whales, dolphins, and porpoises.
Cetaceans are entirely carnivorous. Their ancestors moved their limbs in a vertical plane, and thus cetaceans use vertical strokes when they swim, instead of horizontal strokes like a crocodile or fish.
Cetacean A whale, dolphin or porpoise. Cetaceans A group comprising all whales, dolphins and porpoises. Dorsal fin The unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans.
As I write this unit, I realize that at first glance it might not appear to be useful to many educators because of its rather narrow focus. Its central subject, dolphins .
Cetaceans – whales, dolphins and porpoises – are placental marine regardbouddhiste.com modern members of the infraorder are fully aquatic and live in the open ocean (except a few species of dolphin which inhabit rivers and estuaries).Cetaceans mate, give birth, suckle their young, and feed exclusively underwater.