A Cetacean is defined as a member of the infraorder Cetacea. The word cetacean has a Latin origin, the word when translated into English the cetacean meaning refers to the sea monster. As the name suggests the members of the infraorder are huge and mainly carnivore. The characteristic feature of the members of the infraorder Cetacean is the large streamlined body, carnivorous diet. The Cetacean are mainly found in the marine ecosystem, only rare members are found in the brackish waters. The most commonly known members of the cetacean include whales, dolphins, and porpoises. The rare species that are herbivores includes manatees, dugongs, and Steller’s sea cow. This article focuses on the taxonomic classification, life history, diet, habitat and distribution, and some general anatomical features common to all types of cetacean.
The Cetacean meaning refers to the members of the infraorder Cetacea. They are characterized as aquatic mammals. The taxonomic classification of this group is very important as it serves as an evolutionary link for many organisms. Apart from being the source of the evolutionary links, they are a significant part of the ecosystem and evolutionary studies. The taxonomic classification of Cetaceans are as follows,
The Cetaceans belong to the kingdom Animalia, the kingdom is further classified as a phylum. The cetaceans belong to the phylum Chordata, the unique feature of this phylum is the presence of the vertebral column. The phylum is then further classified into classes. The cetaceans belong to the Mammalia. This unique classification is very important from an evolutionary point of view. The Mammalia is the group of organisms that gives birth to progeny rather than laying eggs and providing parental care to the offspring. This characteristic though seems ordinary, is generally not found in aquatic organisms. Since all the members of Cetacean are aquatic animals, it is rather a unique classification. The class Mammalia gets further classified into order. Cetaceans belong to the order Artiodactyla. The order is classified through its unique feature of even toes, they generally contain 3 to 5 toes, this order generally constitutes the hoofed animals. The order is further classified as a clade, it belongs to a clade named Cetaceamorpha. This clade contains all the dead, living extinct species of the Cetaceans and hippopotamus. The cetaceans belong to the infraorder Cetacea.
There are still various disagreements between evolutionary scientists regarding the taxonomic classification, the major argument is over the suborder and classification of suborders in the taxonomic classification. The classification mentioned above is the widely accepted version of the taxonomic classification.
Examples of Cetacean
The example of cetaceans includes dolphins, porpoises, and all types of whales. The different types of whales include the following: Killer whales, Sperm whales, Beaked whales, Bottlenose whales. The most famous example of a cetacean is a type of whale called the Baleen whale. Baleen whales include whales like the blue whale, the humpback whale, and the bowhead whale. Baleen is actually defined as a filtration system found in above-mentioned whales.
Another example of the member of Cetacea is similar to the dolphins in morphology, but evolutionary and anatomically they are more related to the narwhals and belugas. The species is classified under the family Phocoenidae; there are about 7 living species of the porpoise.
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General Morphological Features
The general features of the cetacean involve body shape, size, and features of the tail. The size of a cetacean varies from species to species needless to say they are among the largest living mammals on planet earth. Among all types of whales the blue whale, which belongs to the baleen whale, is the largest living mammal on earth. The general feature that is discussed in the article is the body surface of a Cetacean.
The distinctive feature that is common in various mammal species except for aquatic mammals like Cetacean is the presence of body hair. Normally mammals have body hair but the Cetaceans lack completely body hair. A partial amount of hair-like features are present near the head or lower jaws but these are believed to work as a sensory receptor. The lack of body hair can be described as an evolutionary adaptation since these organisms are based on the aquatic ecosystem the wet hair will act as poor insulation. The body hair also will add unnecessary weight during the dive.
The colored patches on the epidermis and also the organism living on the body surface of these huge mammals provide distinctive pigmentation. This pigmentation not only helps in identification but also is an important feature of their morphology of the animals themselves.
Since Cetaceans and all the different types of whales are categorized as mammals they lack fins. Fins are the appendage that is common in the fish, they help in locomotion. The locomotive adaptation found in all types of whales is the presence of the flippers. The flippers act like fins; they have shortened arm bones and they lack any distinct finger or finger-like appendages. The flippers help in locomotion by creating vertical strokes rather than horizontal as commonly seen in the fishes. The flippers are modifications of forearms, the hind arm of the mammals are completely lost during the course of evolution, the hind arm is sometimes present as a vestigial organ in some of the species of Cetacean.
External appendages like genitals ears are moved inside the body as an adaptation to aquatic life. In almost all types of whales and other aquatic mammals, there is a presence of a remnant pelvic structure. The only species that lack the pelvic remnants are dwarf and pygmy sperm whales.
Physiological features of all types of whales mentioned in this article include the respiration, circulation, and thermoregulation of the body. It is important to understand the physiology of the animal to have a better understanding of the adaptation and evolutionary changes that Cetacean has undergone to live in the aquatic system, there is some minor difference in these physiological features of Cetacean living in the marine ecosystem and brackish water ecosystem.
The respiration observed in Cetacean is quite interesting, the animals fill the lungs capacity up to 80% in a single breath, the air inhaled is expelled or exhaled during a phenomenon called Blow. The blow of a whale can be seen from a far distance. The reason for this visible blow or exhalation can be attributed to the condensed water of the exhaled air and the accompanied mucous of the respiratory tract. The blow of blue whales can range up to 6 feet. According to cetacean meaning, the organism is of huge size thus the amount of air inhaled is very high also it is interesting to note that the air that fills up the lungs can fill up to *0% of the total capacity.
Similar to most mammals the Cetaceans including different types of whales have a four-chamber of the heart. The heart pumps blood to the complete body. An interesting adaptation seen in all types of whales is the presence of completely developed reservoirs for oxygenated blood called the rete mirabile, the adaptation is specific to the aquatic mammals. This adaptation allows all types of whales, even the largest whale to use up the reserved oxygenated blood during the dive.
Thermoregulation can be defined as the ability to control the temperature of the body. Since it is known that water conducts heat faster as compared to air, the cetaceans including the real whales have this problem of circulation. The largest type of whale is more susceptible to heat loss. To overcome this problem and manage the temperature of the body Cetaceans adapt the three methods which include, evolutionary losing the external appendages to reduce the surface area thus reducing the body heat loss. The second method is the development of blubber. Blubber is the outer covering of the body, made up of fat that acts as an insulation for the body. The blubber is a unique evolutionary adaptation for the real whales and other different Cetaceans. The third and the most important method of thermoregulation is the countercurrent circulation of the body.
The diet of cetaceans includes a wide variety of organisms that are found in the marine ecosystem. All the cetaceans are carnivorous animals, the choice of prey varies from species to species. Whales like sperm whales predate large animals like giant squids, octopuses, and smaller fish. The largest type of whale, like a blue whale or other whales, includes krill, a tiny shrimp-like animal, but fish and copepods (tiny crustaceans). The diet of most baleen whales includes minute drifting mollusks, copepods (1 cm or less), krill (1–5 cm), and small fish and squid up to about 40 cm. It is important to note that though some of the prey is smaller in size but are able to meet the energy requirement of the animal. It is because in a single hunt by all types of whales or as a matter of any cetacean large number of organisms are ingested. An exception to this generalization is some smaller baleen whales like minke baleen (Balaenoptera acutorostrata) that predates individual fishes up to 1 meter in length. The digestive waste of the whales is known as ambergris, the waste product is also known to have commercial value.
Since whales can be classified as toothed and non-toothed whales, the prior is considered as real whales and have evolved from a terrestrial organism having complete dentition, but due to adaptation towards the aquatic ecosystem, the heterodont dentition of the whales got lost. The oral cavity of whales is very large measuring up to five meters long and three meters wide. The stomach of all types of whales is composed of four compartments: forestomach, main stomach, connecting chambers, and pyloric stomach. The main stomach is the true stomach or alternatively known as the digestive stomach. They are lined with epithelial cells that secrete gastric juices and helps in the digestion of the food. The intestine of all types of whales does not have any anatomical differentiation in the small and large intestines.
Habitat and Distribution
Cetaceans are found in almost all types of marine environment ranging from oceans and seas of polar regions to the sea and oceans of the equator. Some of the smaller cetaceans like dolphins and porpoise are also found in the river, but mostly all the large cetaceans are confined to the marine ecosystem. The large population density is seen in areas with abundant food supplies and an environment for reproduction. Some species are coastal, and some are pelagic.
The species of dolphins are found in the freshwater system that is in the river, they are distributed in the following regions, Amazon, Orinoco, La Plata, Yangtze, Ganges, and Indus rivers and surrounding drainage waters.
All different types of whales are found in the entire marine ecosystem, but the majority of them share a pattern of migration. Different types of whales migrate on a latitudinal basis to move between seasonal habitats. One of the major examples is the gray whale, which covers a distance of 5,000-7,000 miles in winter from a colder region to warmer and reproductively preferable Baja California.
Most of the migratory whales that do not cross the equator exception to this generalization is Megaptera novaeangliae, species of the humpback whale and Physeter catodon, a species of the sperm whale. These whales are seen to migrate far in the polar regions.
The cetacean meaning refers to the giant fish or monster. As the name suggests these are huge animals and as a simple theory of ecology the cetacean belongs to k- selected species. Since they belong to this category they do not produce large numbers of progeny from a single mating and provide large parental care to the offspring. Cetaceans are believed to be seasonal breeders, they generally reproduce during winters by migrating towards a warmer region. The reproduction occurs on an average every two years.
Cetaceans are classified as mammals thus they give birth to offspring, the progeny of cetaceans are termed as calves. After birth the calves are dependent on parental care, they are dep[endent on for about 6 months to a year. The females produce rich milk for almost 50% of the fat content. The gestation period among cetaceans ranges from up to 18 months.
Fertilization is an internal process. The male genitalia is located internally as a part of aquatic adaptation but during coitus, they extend out and fertilize the eggs in the female reproductive tract. After fertilization, the gestation period extends up to 12 to 18 months.
Growth and Development
According to cetacean meaning, these organisms constitute the largest mammal living on earth. Sexual dimorphism is observed in the cetaceans. The male of the species or infraorder is larger than the females with some known exceptions. The female baleen whales and some of the beaked whales, river dolphins, and porpoises tend to be slightly larger than males of their species. On the contrary, sperm whales are about 50 percent larger in size than the females of the species.
The whales undergo development for about 5 to 10 years after birth, they develop rapidly during this period. The average range at which growth stops for all the cetaceans ranges from 8 to 25 years of age. This is also defined as the period during which the growth stops. Sexual maturity is achieved at the age of 6 to 10 years. The females are evidenced to ovulate during this period of time. Menopause is not common to all types of whales; rather only some of the species of whales undergo menopause. These species include toothed whale species, killer whales, false killer whales, short-finned pilot whales, belugas, and narwhals.
The average life expectancy of cetaceans ranges from 96 to 100 years. The longest living cetacean is a bowhead, a right whale that can survive for more than 200 years.
The cetaceans are more or less all social animals, they follow a social hierarchy and live with a family or a group that contains two or more families. A group generally contains several close relatives. The group is often termed as a herd, pod, school and, gem. Some of the cetaceans show lifetime association with the group they are involved in. Groups frequently associate with other cetacean species. This is particularly seen in small toothed whales, for example, associations between pilot whales and bottlenose dolphins. Another example is the association between common dolphins and fin whales. Cetaceans are observed to show epimeletic behavior, this can be defined as a behavioral trait of compassion. The animals belonging to this infraorder take care of the injured to smaller members of the pod. Another common behavior is play that is especially seen in the younger members of the pod. This is considered as training for adult life.
Almost all of the cetaceans suffer diseases that are found in the human population. Examples of such diseases include cancer, arthritis, pneumonia, lungworms, tapeworms, and roundworms. The common epidemic found in dolphins and cetaceans include morbillivirus, a disease similar to distemper and measles.
Brucellosis, another common disease, is found in almost all types of whales. They are most visible on humpbacks and gray whales, they occur to a lesser extent on many other baleen and toothed whales. Brucella ceti, a pathogenic bacteria, is responsible for causing chronic diseases and miscarriages. It is also reported to cause male infertility, neurobrucellosis, cardiopathies, bone and skin lesions, strandings, and death.
The cetacean meaning refers to the mammals that belong to the infraorder cetacea. This infraorder contains almost all the whales and porpoises. The members are classified as mammals, they give birth to young ones and provide enough parental care. Most of the animals of this infraorder belong to the marine ecosystem, some of the cetaceans like dolphins belong to the freshwater and brackish water. The average life expectancy of the animal is 90 to 96 years. The animals have a wide range of distribution found in almost all waters, there is a migratory pattern observed in cetaceans. The migration generally occurs towards warmer climates to give birth. The largest type of whale, the blue whale is a member of the cetacean.