The order Cetacea (pronounced /sɨˈteɪʃ(i)ə/, L. cetus, whale, from Greek) includes whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek κῆτος (kētos), meaning "whale" or "any huge fish or sea monster". In Greek mythology the monster Perseus defeated was called Ceto, which is depicted by the constellation of Cetus. Cetology is the branch of marine science associated with the study of cetaceans.
Cetaceans are the mammals best adapted to aquatic life. Their body is fusiform (spindle-shaped). The forelimbs are modified into flippers. The tiny hindlimbs are vestigial; they do not attach to the backbone and are hidden within the body. The tail has horizontal flukes. Cetaceans are nearly hairless, and are insulated by a thick layer of blubber. As a group, they are noted for their high intelligence.
The order Cetacea contains about ninety species, all marine except for four species of freshwater dolphins. The order is divided into two suborders, Mysticeti (baleen whales) and Odontoceti (toothed whales, which includes dolphins and porpoises). The species range in size from Commerson's Dolphin, smaller than a human, to the Blue Whale, the largest animal known to have lived.
Cetaceans are the mammals best adapted to aquatic life. Their body is fusiform (spindle-shaped). The forelimbs are modified into flippers. The tiny hindlimbs are vestigial; they do not attach to the backbone and are hidden within the body. The tail has horizontal flukes. Cetaceans are nearly hairless, and are insulated by a thick layer of blubber. As a group, they are noted for their high intelligence.
The order Cetacea contains about ninety species, all marine except for four species of freshwater dolphins. The order is divided into two suborders, Mysticeti (baleen whales) and Odontoceti (toothed whales, which includes dolphins and porpoises). The species range in size from Commerson's Dolphin, smaller than a human, to the Blue Whale, the largest animal known to have lived.
Respiration
As mammals, cetaceans need to breathe air. Because of this, they need to come to the water's surface to exhale carbon dioxide and inhale a fresh supply of oxygen. During diving, a muscular action closes the blowholes (nostrils), which remain closed until the cetacean next breaks the surface; when it surfaces, the muscles open the blowholes and warm air is exhaled.
Cetaceans' blowholes have evolved to a position on top of the head, allowing more time to expel stale air and inhale fresh air. When the stale air, warmed from the lungs, is exhaled, it condenses as it meets the cold air outside. As with a terrestrial mammal breathing out on a cold day, a small cloud of 'steam' appears. This is called the 'blow' or 'spout' and is different in terms of shape, angle and height, for each cetacean species. Cetaceans can be identified at a distance, using this characteristic, by experienced whalers or whale-watchers.
Cetaceans can go underwater for much longer periods of time than other mammals. Their duration under water varies greatly between species due to large physiological differences between many members of this Order. There are two studied advantages of cetacean physiology that let this Order (and other marine mammals) forage underwater for extended periods of time without breathing at the water surface.
Myoglobin concentrations in skeletal muscle of mammals have much variation. A New Zealand white rabbit has 0.08+/-0.06 g (in a 100 g Wet muscle) of myoglobin,whereas a Northern Bottlenose Whale has 6.34 g (in a 100 g Wet muscle) of myoglobin. Myoglobin, by nature, has a higher affinity to oxygen than hemoglobin. That is, myoglobin retains oxygen molecules better than hemoglobin. Therefore, it is useful to have higher concentrations of myoglobin when needed and there is no oxygen available for re-uptake. The higher the myoglobin concentration in cetacean skeletal muscle, the longer they can stay underwater and forage.
Increased body size is another way of elongating dive duration of large cetaceans. This is true because of two considered aspects. An increase in body size means that there is increase in muscle mass, therefore, increase in muscle oxygen stores. Another aspect is the universal correlation of mass and metabolic rate (Kleiber's law). In layman’s terms, Kleiber’s law states that the metabolic rate of a large animal is slower than a small animal per unit mass. From this we can conclude that larger animals will use up less oxygen than smaller animals
Cetaceans' blowholes have evolved to a position on top of the head, allowing more time to expel stale air and inhale fresh air. When the stale air, warmed from the lungs, is exhaled, it condenses as it meets the cold air outside. As with a terrestrial mammal breathing out on a cold day, a small cloud of 'steam' appears. This is called the 'blow' or 'spout' and is different in terms of shape, angle and height, for each cetacean species. Cetaceans can be identified at a distance, using this characteristic, by experienced whalers or whale-watchers.
Cetaceans can go underwater for much longer periods of time than other mammals. Their duration under water varies greatly between species due to large physiological differences between many members of this Order. There are two studied advantages of cetacean physiology that let this Order (and other marine mammals) forage underwater for extended periods of time without breathing at the water surface.
Myoglobin concentrations in skeletal muscle of mammals have much variation. A New Zealand white rabbit has 0.08+/-0.06 g (in a 100 g Wet muscle) of myoglobin,whereas a Northern Bottlenose Whale has 6.34 g (in a 100 g Wet muscle) of myoglobin. Myoglobin, by nature, has a higher affinity to oxygen than hemoglobin. That is, myoglobin retains oxygen molecules better than hemoglobin. Therefore, it is useful to have higher concentrations of myoglobin when needed and there is no oxygen available for re-uptake. The higher the myoglobin concentration in cetacean skeletal muscle, the longer they can stay underwater and forage.
Increased body size is another way of elongating dive duration of large cetaceans. This is true because of two considered aspects. An increase in body size means that there is increase in muscle mass, therefore, increase in muscle oxygen stores. Another aspect is the universal correlation of mass and metabolic rate (Kleiber's law). In layman’s terms, Kleiber’s law states that the metabolic rate of a large animal is slower than a small animal per unit mass. From this we can conclude that larger animals will use up less oxygen than smaller animals
Vision, hearing and echolocation
Cetacean eyes are set well back and to either side of its head. This means that cetaceans with pointed 'beaks' (such as dolphins) have good binocular vision forward and downward but others, with blunt heads (such as the Sperm Whale), can see either side but not directly ahead or directly behind. Tear glands secrete greasy tears, which protect the eyes from the salt in the water. Cetaceans also have an almost spherical lens in their eyes, which is most efficient at focusing what little light there is in the deep waters. Cetaceans make up for their generally quite poor vision (with the exception of the dolphin) with excellent hearing.
As with the eyes, cetacean ears are also small. Life in the sea accounts for the cetacean's loss of its external ears, whose function is to collect airborne sound waves and focus them in order for them to become strong enough to hear well. However, water is a better conductor of sound than air, so the external ear was no longer needed: it is no more than a tiny hole in the skin, just behind the eye. The inner ear, however, has become so well developed that the cetacean can not only hear sounds dozens of miles away, but it can also discern from which direction the sound comes.
Some cetaceans are capable of echolocation. Many toothed whales emit clicks similar to those in echolocation, but it has not been demonstrated that they echolocate. Mysticeti have little need of echolocation, as they prey upon small fish that would be impractical to locate with echolocation. Some members of Odontoceti, such as dolphins and porpoises, do perform echolocation. These cetaceans use sound in the same way as bats—they emit a sound (called a click), which then bounces off an object and returns to them. From this, cetaceans can discern the size, shape, surface characteristics and movement of the object, as well as how far away it is. With this ability cetaceans can search for, chase and catch fast-swimming prey in total darkness. Echolocation is so advanced in most Odontoceti that they can distinguish between prey and non-prey (such as humans or boats); captive cetaceans can be trained to distinguish between, for example, balls of different sizes or shapes.
Cetaceans also use sound to communicate, whether it be groans, moans, whistles, clicks or the complex 'singing' of the Humpback Whale.
As with the eyes, cetacean ears are also small. Life in the sea accounts for the cetacean's loss of its external ears, whose function is to collect airborne sound waves and focus them in order for them to become strong enough to hear well. However, water is a better conductor of sound than air, so the external ear was no longer needed: it is no more than a tiny hole in the skin, just behind the eye. The inner ear, however, has become so well developed that the cetacean can not only hear sounds dozens of miles away, but it can also discern from which direction the sound comes.
Some cetaceans are capable of echolocation. Many toothed whales emit clicks similar to those in echolocation, but it has not been demonstrated that they echolocate. Mysticeti have little need of echolocation, as they prey upon small fish that would be impractical to locate with echolocation. Some members of Odontoceti, such as dolphins and porpoises, do perform echolocation. These cetaceans use sound in the same way as bats—they emit a sound (called a click), which then bounces off an object and returns to them. From this, cetaceans can discern the size, shape, surface characteristics and movement of the object, as well as how far away it is. With this ability cetaceans can search for, chase and catch fast-swimming prey in total darkness. Echolocation is so advanced in most Odontoceti that they can distinguish between prey and non-prey (such as humans or boats); captive cetaceans can be trained to distinguish between, for example, balls of different sizes or shapes.
Cetaceans also use sound to communicate, whether it be groans, moans, whistles, clicks or the complex 'singing' of the Humpback Whale.
