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Mammals

Mammals (class Mammalia) are vertebrate animals characterized by the presence of sweat glands, including milk producing sweat glands, and by the presence of: hair, three middle ear bones used in hearing, and a neocortex region in the brain. Mammals, other than the monotremes, give birth to live young instead of laying eggs. They also possess specialized teeth and use a placenta in the ontogeny. The mammalian brain regulates endothermic and circulatory systems, including a four-chambered heart. Mammals encompass approximately 5,400 species, ranging in size from the Bumblebee Bat, (30-40mm), to the Blue Whale, (33,000mm), distributed in about 1,200 genera, 153 families, and 29 orders, though this varies by classification scheme.

Most mammals belong to the placental group. The four largest orders within the placental mammals are Rodentia (mice, rats, and other small, gnawing mammals), Chiroptera (bats), Carnivora (dogs, cats, bears, and other mammals that primarily eat meat), and Cetartiodactyla (including numerous herbivore species, such as deer, sheep, goats, and buffalos, plus whales).

Phylogenetically, Mammalia is defined as all descendants of the most recent common ancestor of monotremes (e.g., echidnas and platypuses) and therian mammals (marsupials and placentals). This means that some extinct groups of "mammals" are not members of the crown group Mammalia, even though most of them have all the characteristics that traditionally would have classified them as mammals. These "mammals" are now usually placed in the unranked clade Mammaliaformes.

The mammalian line of descent diverged from the sauropsid line at the end of the Carboniferous period. The sauropsids would evolve into modern-day reptiles and birds, while the synapsid branch led to mammals. The first true mammals appeared in the Jurassic period. Modern mammalian orders appeared in the Palaeocene and Eocene epochs of the Palaeogene period.

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The Island Fox(Urocyon littoralis) is a small foxthat is native to six of the eight Channel Islands of California. It is the smallest fox species in the United States. There are six subspecies of the fox, each unique to the island it inhabits, reflecting its evolutionary history. Other names for the Island Fox include Coast Fox, Short-Tailed Fox, Island Gray Fox, Channel Islands Fox, Channel Islands Gray Fox, California Channel Island Fox and Insular Gray Fox. The Island Fox shares the Urocyon genuswith the mainland Gray Fox, the fox from which it is descended. Its small size is a result of island dwarfing, a kind of allopatric speciation. Because Island Foxes are geographically isolated they have no immunityto parasitesand diseases brought in from the mainland and are especially vulnerable to those domestic dogs may carry. In addition, Golden Eaglepredation and human activities devastated fox numbers on several of the Channel Islands in the 1990s. Four Island Fox subspecies were federally protected as an endangered speciesin 2004, and efforts to rebuild fox populations and restore the ecosystems of the Channel Islands are being undertaken. ...Archive/Nominations

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Credit: Fir0002

The Domestic Sheep (Ovis aries) is the most common species of the sheep genus. It is a woolly ruminant quadruped that probably descended from the wild moufflon. Many breeds of sheep exist, generally classified as wool class breeds and hair class breeds. Farmers develop wool breeds for superior wool quantity and quality (fineness of fibers), wool staple length and degree of crimp in the fiber. Hair class sheep are the original class of sheep, developed worldwide for meat and leather.

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Scientific classification

Kingdom→ Animalia Phylum→ Chordata Subphylum→ Vertebrata (unranked)→ Amniota Class→ Mammalia

Subclasses and Infraclasses

Subclass †Allotheria*
Subclass Prototheria
Subclass Theria
- Infraclass †Trituberculata
- Infraclass Metatheria
- Infraclass Eutheria

* Member of a haplogroup and not any of its subclades.
† Taxa is extinct.

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Topics

Monotremata · Didelphimorphia · Paucituberculata · Microbiotheria · Notoryctemorphia · Dasyuromorphia · Peramelemorphia · Diprotodontia · Afrosoricida · Macroscelidea · Tubulidentata · Hyracoidea · Proboscidea · Sirenia · Cingulata · Pilosa · Scandentia · Dermoptera · Primates · Rodentia · Lagomorpha · Erinaceomorpha · Soricomorpha · Chiroptera · Pholidota · Carnivora · Perissodactyla · Artiodactyla · Cetacea edit

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WikiProjects

A complete list of scientific WikiProjects can be found here. See also Wikispecies, a Wikimedia project dedicated to classification of biological species.

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