Mammal
hideMammals (formally Mammalia) are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.
Mammals are divided into three main categories depending how they are born. These categories are, monotremes, marsupials and placentals. Except for the five species of monotremes (which lay eggs), all mammal species give birth to live young. Most mammals also possess specialized teeth, and the largest group of mammals, the placentals, use a placenta during gestation. The mammalian brain regulates endothermic and circulatory systems, including a four-chambered heart.
There are approximately 5,400 species of mammals, distributed in about 1,200 genera, 153 families, and 29 orders (though this varies by classification scheme). Mammals range in size from the 30–40-millimetre (1.2–1.6 in) Bumblebee Bat to the 33-metre (110 ft) Blue Whale.
Mammals are divided into two subclasses, the prototheria, which includes the oviparous monotremes, and the theria, which includes the placentals and live-bearing marsupials. Most mammals, including the six largest orders, belong to the placental group. The three largest orders, in descending order, are Rodentia (mice, rats, and other small, gnawing mammals), Chiroptera (bats), and Soricomorpha (shrews, moles and solenodons). The next three largest orders include the Carnivora (dogs, cats, weasels, bears, seals, and their relatives), the Cetartiodactyla (including the even-toed hoofed mammals and the whales) and the Primates to which the human species belongs. The relative size of these latter three orders differs according to the classification scheme and definitions used by various authors.
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 an amniote line at the end of the Carboniferous period. One line of amniotes would lead to reptiles, while the other would lead to synapsids, including mammals. The first true mammals appeared in the Triassic period. Modern mammalian orders appeared in the Palaeocene and Eocene epochs of the Palaeogene period.
For more information about Mammal, read the full article at
Wikipedia.
This text uses material from Wikipedia and is available under the GNU Free Documentation License.
News tagged with mammals
Warm-blooded dinosaurs worked up a sweat
Nov 11, 2009 |
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(PhysOrg.com) -- Were dinosaurs endothermic (warm-blooded) like present-day mammals and birds or ectothermic (cold-blooded) like present-day lizards? The implications of this simple-sounding question go beyond ...
Humans, Other Mammals Similarly Voice Frustrations
Nov 05, 2009 |
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Pet owners and scientists who spend a lot of time in the wild say that they can tell when an animal is upset by the sound of its voice. Now new analyses of animal calls may offer an explanation; humans seem ...
Discovery of the oldest European marsupial
Other Sciences / Archaeology & Fossils
Nov 04, 2009 |
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(PhysOrg.com) -- Remains of one of the oldest known marsupials have been recovered in Charente-Maritime by a palaeontologist team from the Muséum national d'Histoire naturelle (CNRS, France) and the ...
Research study on the European mink, Mustela lutreola
Nov 02, 2009 |
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The European mink, Mustela lutreola, is a species catalogued as in danger of extinction, due to the large decline in their population over the past century. It is considered to be one of the most endangered mammals, both l ...
New insights into Australia's unique platypus
Nov 02, 2009 |
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(PhysOrg.com) -- New insights into the biology of the platypus and echidna have been published, providing a collection of unique research data about the world's only monotremes.
Paleontologists discover a new Mesozoic mammal
Other Sciences / Archaeology & Fossils
Oct 08, 2009 |
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Pittsburgh, Pennsylvania, USA…An international team of paleontologists has discovered a new species of mammal that lived 123 million years ago in what is now the Liaoning Province in northeastern China. The ...
Small mammals have a 'Celtic fringe' too
Sep 30, 2009 |
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The origin of the 'Celtic fringe' of genetically and culturally distinctive people in the northern and western British Isles is the source of fierce academic controversy.
10 percent of world's major species at threat: report
Sep 29, 2009 |
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Almost 10 percent of the world's mammals, birds, reptiles, amphibians and fish are in danger of extinction due to climate change and other factors, according to an Australian report released Tuesday.
Photoswitches shed light on spontaneous free swimming in zebrafish (w/ Video)
Sep 16, 2009 |
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A new way to select and switch on one cell type in an organism using light has helped answer a long-standing question about the function of one class of enigmatic nerve cells in the spinal cord.
Man indicted in death of Hawaiian monk seal
Aug 06, 2009 |
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(AP) -- A federal grand jury has indicted a 78-year-old Kauai man in the shooting death of an endangered Hawaiian monk seal in May.
Naming evolution's winners and losers
Jul 29, 2009 |
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(PhysOrg.com) -- Mammals and many species of birds and fish are among evolution's "winners," while crocodiles, alligators and a reptile cousin of snakes known as the tuatara are among the losers, according ...
Trees evolved camouflage defense against long extinct predator: First evidence of camouflage defense in plants
Jul 22, 2009 |
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(PhysOrg.com) -- Many animal species such as snakes, insects and fish have evolved camouflage defences to deter attack from their predators. However research published in New Phytologist has discovered that t ...
Researchers look to imprinted genes for clues to fetal growth restriction in cloned swine
Jul 20, 2009 |
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(PhysOrg.com) -- Researchers at North Carolina State University have found that intrauterine growth restriction (IUGR), which results in low birth weight and long-term deleterious health effects in cloned swine, is linked ...
House cats know what they want and how to get it from you
Jul 13, 2009 |
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Anyone who has ever had cats knows how difficult it can be to get them to do anything they don't already want to do. But it seems that the house cats themselves have had distinctly less trouble getting humans ...
Scientists identify enzyme important in aging
Jul 10, 2009 |
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The secret to longevity may lie in an enzyme with the ability to promote a robust immune system into old age by maintaining the function of the thymus throughout life, according to researchers studying an "anti-aging" mouse ...
