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
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News tagged with mammal
Small faults in Southeast Spain reduce earthquake risk of larger ones
Space & Earth / Earth Sciences
Nov 25, 2009 |
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A team of Spanish scientists, studying recent, active deformations in the Baetic mountain range, have shown that the activity of smaller tectonic structures close to larger faults in the south east of the ...
Sharks under threat as environmental change bites hard
Nov 17, 2009 |
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(PhysOrg.com) -- Their size and fearsome appearance have made them the stuff of nightmares, but new research just published suggests that sharks may not be as tough as they appear.
Feds give sea otters habitat protection in Alaska
Oct 08, 2009 |
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(AP) -- Four years after being placed on the Endangered Species List, the dwindling sea otters of southwest Alaska on Wednesday were given an important recovery tool.
Albatross camera reveals fascinating feeding interaction with killer whale
Oct 07, 2009 |
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Scientists from British Antarctic Survey, National Institute of Polar Research, Tokyo, and Hokkaido University, Japan, have recorded the first observations of how albatrosses feed alongside marine mammals ...
Extinct Mammal Used its 'Sweet Spot' to Club Rivals
Aug 27, 2009 |
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(PhysOrg.com) -- Scientists in Uruguay studying extinct mammals called glyptodonts have discovered they used a "sweet spot" in their tails, just like baseball players use the center of percussion (CP), or ...
Research finds higher acidity in Alaska waters
Space & Earth / Earth Sciences
Aug 24, 2009 |
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(AP) -- Erosion threatens to topple coastal Alaskan villages. Melting ice threatens polar bears. Now, a marine scientist says the state's marine waters are turning acidic from absorbing greenhouse gases faster ...
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.
Orangutans unique in movement through tree tops
Jul 27, 2009 |
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Movement through a complex meshwork of small branches at the heights of tropical forests presents a unique challenge to animals wanting to forage for food safely. It can be particularly dangerous for large ...
Ancient mammal tracks found at national monument
Other Sciences / Archaeology & Fossils
Jul 24, 2009 |
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(AP) -- Hundreds of tiny footprints left by mammals some 190 million years ago have been found on a canyon wall in a remote part of Dinosaur National Monument, park officials said Thursday.
All in sight: Scientists test infrared system for the protection of whales
Jul 02, 2009 |
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A new measurement system for the detection of whales is used for the first time on board of the research vessel Polarstern. Whales are usually difficult to spot. On the one hand, they spend the greater part ...
Natural-born divers and the molecular traces of evolution
Jun 29, 2009 |
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An aquatic lifestyle imposes serious demands for the organism, and this is true even for the tiniest molecules that form our body. When the ancestors of present marine mammals initiated their return to the oceans, their ...
Scientists find tiny new bat species: Geneva museum
Jun 24, 2009 |
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Scientists have identified a new species of bat weighing just five grammes in the Comoros island archipelago off eastern Africa, the Natural History Museum in Geneva said on Wednesday.
'Bycatch' whaling a growing threat to coastal whales
Jun 23, 2009 |
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Scientists are warning that a new form of unregulated whaling has emerged along the coastlines of Japan and South Korea, where the commercial sale of whales killed as fisheries "bycatch" is threatening coastal stocks of minke ...
Sick sea critters aided by Marine Mammal Center
Jun 14, 2009 |
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(AP) -- A recent surge in weakened and malnourished sea lions found along the Northern California coast is mystifying scientists and keeping workers hopping at the newly expanded Marine Mammal Center here.
Hawaiian Islands named habitat for endangered seal
Jun 12, 2009 |
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(AP) -- The federal government on Friday will significantly expand the critical habitat for endangered Hawaiian monk seals to include beaches and waters of the main Hawaiian Islands, officials said.
