Marine mammals are a diverse group of roughly 120 species of mammal that are primarily ocean-dwelling or depend on the ocean for food. The humpback whale ( Megaptera novaeangliae) is a Baleen Whale. The Order Cetacea (sɪˈteɪʃiə L cetus, whale includes Whales Dolphins and Porpoises Cetus is The Leopard seal ( Hydrurga leptonyx) is the second largest species of seal in the Antarctic (after the Southern Elephant Seal) and is near the top Pinnipeds ("fin-feet" lit "winged feet" or fin-footed mammals are a widely distributed and diverse group of semi-aquatic marine Mammals comprising The diverse order Carnivora (kɑrˈnɪvərə or sometimes /ˌkɑrnɪˈvɔərə/ from Latin carō (stem carn-) "flesh" + vorāre The West Indian Manatee ( Trichechus manatus) is a Manatee, and the largest surviving member of the aquatic mammal order Sirenia (which also includes Not to be confused with order Sirenidae (aquatic salamanders For the Gothic metal band see Sirenia (band Sirenia The sea otter ( Enhydra lutris) is a Marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Mustelidae or Mustelids (from Latin mustela, Weasel) commonly referred to as the weasel family, is a family of carnivorous Mammals The polar bear ( Ursus maritimus) is a Bear native to the Arctic Ocean and its surrounding seas Mammals ( class Mammalia) are a class of Vertebrate Animals characterized by the presence of Sweat glands, including sweat glands An ocean (from Greek, ''Okeanos'' (Oceanus) is a major body of saline water, and a principal component of the Hydrosphere. They include the cetaceans (whales, dolphins, and porpoises), the sirenians (manatees and dugong), the pinnipeds (true seals, eared seals and walrus), and several otters (the sea otter and marine otter). The Order Cetacea (sɪˈteɪʃiə L cetus, whale includes Whales Dolphins and Porpoises Cetus is Whales are marine mammals which are neither Dolphins (ie members of the families Delphinidae or Platanistoidae) nor Porpoises Orcas Dolphins are Marine mammals that are closely related to Whales and Porpoises There are almost forty species of dolphin in seventeen genera. Porpoises are Small Cetaceans of the Family Phocoenidae; they are related to Whales and Dolphins They are distinct from dolphins Not to be confused with order Sirenidae (aquatic salamanders For the Gothic metal band see Sirenia (band Sirenia Manatees ( family Trichechidae, Genus Trichechus) are large fully aquatic Marine mammals sometimes known as sea The dugong ( Dugong dugon) is a large Marine Mammal which together with the Manatees is one of four living species of the order Sirenia Pinnipeds ("fin-feet" lit "winged feet" or fin-footed mammals are a widely distributed and diverse group of semi-aquatic marine Mammals comprising The true seals or earless seals are one of the three main groups of Mammals within the seal Suborder, Pinnipedia. The eared seals or otariids are Marine mammals in the family Otariidae - one of three groupings of Pinnipeds. The walrus ( Odobenus rosmarus) is a large flippered Marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and Otters are semi- aquatic (or in one case aquatic) fish-eating Mammals The otter subfamily Lutrinae forms part of the family The sea otter ( Enhydra lutris) is a Marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Marine Otters (Lontra felina are rare and poorly-known Marine mammals of the weasel family (Family Mustelidae) The polar bear is also usually grouped with the marine mammals. The polar bear ( Ursus maritimus) is a Bear native to the Arctic Ocean and its surrounding seas

Marine mammals evolved from land dwelling ancestors and share several adaptive features for life at sea such as generally large size, hydrodynamic body shapes, modified appendages and various thermoregulatory adaptations. Fluid dynamics is the sub-discipline of Fluid mechanics dealing with fluid flow: Fluids ( Liquids and Gases in motion An appendage in the broadest sense is an additional or subsidiary part existing on or added to something which can generally still function if the appendage has never existed or Thermoregulation is the ability of an Organism to keep its body temperature within certain boundaries even when temperature surrounding is very different Different species are, however, adapted to marine life to varying degrees. The most fully adapted are the cetaceans and the sirenians, whose entire life cycle takes place under water, whereas the other groups spend at least some time on land.

Despite the fact that marine mammals are highly recognizable charismatic megafauna, many populations are vulnerable or endangered due to a history of commercial exploitation for blubber, meat, ivory and fur. Charismatic megafauna are large animal species with widespread popular appeal that Environmental activists use to achieve conservation goals well beyond An endangered species is a population of an organism which is at risk of becoming Extinct because it is either few in numbers or threatened by changing environmental or predation Blubber is a thick layer of vascularized Fat found under the skin of all Cetaceans Pinnipeds and Sirenians Description In modern English usage meat most often refers to Animal tissue used as food mostly Skeletal muscle and associated Fat, but it may also refer Ivory is formed from Dentine and constitutes the bulk of the Teeth and Tusks of animals such as the Elephant, Hippopotamus, Fur is a body hair of any non-human Mammal, also known as the Pelage. Most species are currently protected from commercial exploitation.

Contents 1 Groups 2 Adaptations 3 Research 4 References 5 See also 6 External links

Groups

There are some 120 extant species of marine mammals, generally subdivided into the five groups bold-faced below. ^[1]

• Order Sirenia: Sirenians
  • family Trichechidae: manatees (3 species)
  • family Dugongidae: dugong (1 species)
• Order Cetacea: Cetaceans
  • Suborder Mysticeti: Baleen whales (14 or 15 species)
  • Suborder Odontoceti: Toothed whales (around 73 species)
• Order Carnivora,
  • superfamily Pinnipedia
    • family Phocidae: true seals (around 20 species)
    • family Otariidae: eared seals (around 16 species)
    • family Odobenidae: walrus (1 species)
  • family Mustelidae
    • sea otter (Enhydra lutris)
    • marine otter (Lontra felina)
  • family Ursidae
    • polar bear (Ursus maritimus)

The sirenians and cetaceans are thought to be descendent from an ungulate ancestor, while the pinnipeds, otters and polar bear are descended from a caniform ancestor. This article is about the taxonomic rank for the sequence of species in a taxonomic list see Taxonomic order In scientific classification used Not to be confused with order Sirenidae (aquatic salamanders For the Gothic metal band see Sirenia (band Sirenia The Order Cetacea (sɪˈteɪʃiə L cetus, whale includes Whales Dolphins and Porpoises Cetus is The baleen whales, also called whalebone whales or great whales, form the Mysticeti, one of two suborders of the Cetacea (whales dolphins and The toothed whales ( Systematic name Odontoceti) form a Suborder of the Cetaceans including sperm whales beaked whales orca dolphins The diverse order Carnivora (kɑrˈnɪvərə or sometimes /ˌkɑrnɪˈvɔərə/ from Latin carō (stem carn-) "flesh" + vorāre Pinnipeds ("fin-feet" lit "winged feet" or fin-footed mammals are a widely distributed and diverse group of semi-aquatic marine Mammals comprising The true seals or earless seals are one of the three main groups of Mammals within the seal Suborder, Pinnipedia. The eared seals or otariids are Marine mammals in the family Otariidae - one of three groupings of Pinnipeds. The walrus ( Odobenus rosmarus) is a large flippered Marine mammal with a discontinuous circumpolar distribution in the Arctic Ocean and Mustelidae or Mustelids (from Latin mustela, Weasel) commonly referred to as the weasel family, is a family of carnivorous Mammals The sea otter ( Enhydra lutris) is a Marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Marine Otters (Lontra felina are rare and poorly-known Marine mammals of the weasel family (Family Mustelidae) The polar bear ( Ursus maritimus) is a Bear native to the Arctic Ocean and its surrounding seas Ungulates (meaning roughly "being Hoofed quot or "hoofed animal" are several groups of Mammals most of which use the tips of their toes usually Caniformia, or Canoidea (literally " dog-like " are a Suborder within the order Carnivora. The morphological similarities between these diverse groups are a result of convergent and parallel evolution. The term morphology in Biology refers to the outward appearance ( Shape, Structure, Colour, Pattern) of an Organism Convergent evolution describes the acquisition of the same biological trait in unrelated lineages Parallel evolution is the independent evolution of similar traits starting from a similar ancestral condition due to similar environments or other evolutionary pressures

Adaptations

Since mammals originally evolved on land, their spines are optimized for running, allowing for up-and-down but only little sideways motion. In Human anatomy, the vertebral column ( backbone or spine) is a column of 34 Vertebrae the Sacrum, Intervertebral Therefore, marine mammals typically swim by moving their spine up and down. By contrast, fish normally swim by moving their spine sideways. For this reason, fish mostly have vertical caudal (tail) fins, while marine mammals have horizontal caudal fins.

Some of the primary differences between marine mammals and other marine life are:

• Marine mammals breathe air, while most other marine animals extract oxygen from water.
• Marine mammals have hair. Cetaceans have little or no hair, usually a very few bristles retained around the head or mouth. The Order Cetacea (sɪˈteɪʃiə L cetus, whale includes Whales Dolphins and Porpoises Cetus is All members of the Carnivora have a coat of fur or hair, but it is far thicker and more important for thermoregulation in sea otters and polar bears than in seals or sea lions. The diverse order Carnivora (kɑrˈnɪvərə or sometimes /ˌkɑrnɪˈvɔərə/ from Latin carō (stem carn-) "flesh" + vorāre Thermoregulation is the ability of an Organism to keep its body temperature within certain boundaries even when temperature surrounding is very different The sea otter ( Enhydra lutris) is a Marine mammal native to the coasts of the northern and eastern North Pacific Ocean. The polar bear ( Ursus maritimus) is a Bear native to the Arctic Ocean and its surrounding seas Pinnipeds ("fin-feet" lit "winged feet" or fin-footed mammals are a widely distributed and diverse group of semi-aquatic marine Mammals comprising For other uses of the term "sea lion" see Sea lion (disambiguation. Thick layers of fur contribute to drag while swimming, and slow down a swimming mammal, giving it a disadvantage in speed.
• Marine mammals have thick layers of blubber used to insulate their bodies and prevent heat loss. Blubber is a thick layer of vascularized Fat found under the skin of all Cetaceans Pinnipeds and Sirenians Description Sea otters and polar bears are exceptions, relying more on fur and behavior to stave off hypothermia. The polar bear ( Ursus maritimus) is a Bear native to the Arctic Ocean and its surrounding seas
• Marine mammals give birth. Most marine mammals give birth to one calf or pup at a time.
• Marine mammals feed off milk as young. Maternal care is extremely important to the survival of offspring that need to develop a thick insulating layer of blubber. Blubber is a thick layer of vascularized Fat found under the skin of all Cetaceans Pinnipeds and Sirenians Description The milk from the mammary glands of marine mammals often exceeds 40-50% fat content to support the development of blubber in the young. Mammary glands are the organs that in Mammals produce Milk for the sustenance of the young
• Marine mammals maintain a high internal body temperature. Unlike most other marine life, marine mammals carefully maintain a core temperature much higher than their environment. Blubber, thick coats of fur, bubbles of air between skin and water, countercurrent exchange, and behaviors such as hauling out, are all adaptations that aid marine mammals in retention of body heat. Blubber is a thick layer of vascularized Fat found under the skin of all Cetaceans Pinnipeds and Sirenians Description Fur is a body hair of any non-human Mammal, also known as the Pelage. Countercurrent exchange is a mechanism used to transfer some property of a Fluid from one flowing current of fluid to another across a Semipermeable membrane or thermally-conductive An adaptation is a characteristic of an Organism that has been favored by Natural selection and

The polar bear spends a large portion of its time in a marine environment, albeit a frozen one. The polar bear ( Ursus maritimus) is a Bear native to the Arctic Ocean and its surrounding seas When it does swim in the open sea it is extremely proficient and has been shown to cover 74 km in a day. For these reasons, some scientists regard it as a marine mammal.

Research

Considerable research has been conducted on the incidence of diseases that afflict marine mammals in the marine environment. This work has addressed leptospirosis, phocine herpesvirus, neurological diseases, toxicology^[2] and other pathologies affecting marine mammals. Leptospirosis (also known as Weil's disease, canicola fever, canefield fever, nanukayami fever, 7-day fever and many more is a The Herpesviridae are a large family of DNA viruses that cause diseases in animals including humans Entire research organizations have developed such as the Marine Mammal Center to focus upon the rehabilitation and research functions of marine mammals. The Marine Mammal Center is a private non-profit US organization centered on rescue rehabilitation environmental research and education regarding Marine mammals

References

See also

• Institute for Marine Mammal Studies

External links

• Read Congressional Research Service (CRS) Reports regarding Marine mammals
• A 2005 Report by the National Academy of Sciences entitled Marine Mammal Populations and Ocean Noise, is available for free online reading and research
• University of Washington Libraries Digital Collections -- Freshwater and Marine Image Bank -- Aquatic Mammals An ongoing digital collection of images related to marine and aquatic mammals. The Institute for Marine Mammal Studies ("IMMS" is a major non-profit organization established in 1984 for the education conservation and research on Marine mammals The National Academy of Sciences (NAS is a corporation in the United States whose members serve Pro bono as "advisers to the nation on science
• Marine Mammal Resource

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