Nounmammals
From Wiktionary under the GNU Free Documentation License. Mammals (formally Mammalia) are a class of vertebrate, air-breathing animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair and/or fur, three middle ear bones used in hearing, and a neocortex region in the brain. Mammals are divided into three main infraclass taxa depending how they are born. These taxa 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 millimeter (1- to 1.5-inch) Bumblebee Bat to the 33-meter (108-foot) 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, porcupines, beavers, capybaras, and other 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. According to cladistics, mammals are a sub-group of synapsids. Although they were preceded by many diverse groups of non-mammalian synapsids (sometimes misleadingly referred to as mammal-like reptiles), the first true mammals appeared in the Triassic period. Modern mammalian orders appeared in the Palaeocene and Eocene epochs of the Palaeogene period. From Wikipedia under the
GNU Free Documentation License Why do male mammals have ridiculously oversized genitalia? Q. I am not trying to be gross or anything, but it is just something I have noticed over the years working with various animals. Reptiles or birds lack this odd quality, but it is predominant in all mammals including human males (which even at the smallest is ridiculously large), and tiny animals such as squirrels or cats. Is there a breeding reason for this? Asked by nightwoman77 - Sun Feb 1 04:25:09 2009 - - 20 Answers - 0 Comments A. Not so. First thing, mammals have a breeding season. When males are ready to breed their genital are larger. Each species evolves its size according with the females genitalia. When males are not breeding the external male anatomy may be difficult to see. This characteristic is also a clue to the female as to the reproductive state of the male. And may have a secondary behavioral meaning. The average length of a human male penis is 6 inches. Accordingly, that's about the same distant from the outside of the vagina to the cervix. And wrong about the smallest human penis being ridiculously large. A male with a short penis may not be able to fertilizer a woman. I would say your powers of observation need a check up. Answered by Jim - Sun Feb 1 08:08:13 2009 How are other mammals nourished in the womb? Q. I was talking to my husband today, and that came up for some reason. He says that only humans have umbilical cords and belly buttons. But that seems wrong to me. I think I've heard somewhere that cows have umbilical cords. Anywho, I feel silly that I don't know this already...but can someone help set us straight? Do other mammals have umbilical cords and if so, how is it detached without harming the baby or mother (like if it's done wrong with humans, they bleed out) in nature? And if not, what do they have for en utero nourishment? Asked by Mabe - Thu Dec 14 15:25:33 2006 - - 3 Answers - 1 Comments A. All placental mammals have umbilical cords. After birth the umbilical cord is either chewed or stretched and broken into, depending on the animal. And yes, they do have bellybuttons. Check out a dog or cat to see for yourself. They don't look quite like ours but they are there. Other types of mammals are Monotremita - egg laying, and Marsupial - pouched. Answered by myste - Thu Dec 14 15:42:38 2006 What are some useful facts about evolution - birds mammals and reptiles?
Q. I am doing a Science SA and i dont know much about the evolution of birds mammals and reptiles, as this is one of my points. Here is my question if you have some ideas on how to help me Birds and mammals re more alike than birds and reptiles . By examining the features of the three groups, comment on this statement with supporting evidence. (ie. Do you agree or disagree with this statement?). Asked by Hannah M - Tue Apr 22 05:50:25 2008 - - 1 Answers - 1 Comments A. Birds are actually a part of the reptile lineage, and are therefore much more closely related to present day reptiles than mammals. Their only similarity to mammals is their endothermy (warm blood), but otherwise they are much more like reptiles (see In your essay you may want to mention the jaw bones, as the articulation of the squamosal and dentary bones is actually the defining feature of mammals (and only mammals). Answered by bugman - Tue Apr 22 08:01:23 2008 From Yahoo Answer Search: "mammals"  news.google.com Contra Costa Times "This was something never before done with free swimming mammals ," said Oswald. "It was very dangerous." But Oswald also said the capture was a textbook ... and more » news.google.com Sharon Advocate Other mammals , such as the Eastern chipmunk and fox and gray squirrels, have periods of torpor during which they drop their body temperature into the 60s. ... and more » news.google.com NavyTimes.com These include trained lookouts on bridges to identify marine mammals , course changes to avoid marine mammals , and reducing or shutting down active sonar ... From Google News Search: "mammals"  longitudebooks.com 314px x 200px | 45.20kB [source page] Peru Mammals Guide Rainforest Publications  image.guardian.co.uk 192px x 372px | 24.10kB [source page] The Guardian Invigorating Niamh Cusack Helena Lymbery Daniel Ryan and Jane Hazlegrove in Mammals Photo Tristram Kenton From Yahoo Image Search: "mammals"  animals.about.com unknown Sun, 27 Dec 2009 22:42:16 GM Mammals. (Class Mammalia) are one of the six basic groups of animals. . Mammals. are a group of vertebrates that includes about 5000 species that range in size from the minute Bumblebee Bat which measures a mere 4cm to the collasal Blue ...  contracostatimes.com By Gary Bogue Contra Costa Times hu, 21 Jan 2010 15:49:38 GM Rescuers are having trouble catching an injured sea lion and a reader suggests they tranquilize it. Gary says it s not that simple.  naturalvisionsphoto.com Kevin, FCD Mon, 25 Jan 2010 13:52:10 GM Wood Bison, British Columbia (click image to view larger) In northern British Columbia & Alberta, as well as the southern portion of the Northwest Territories, you may encounter bison in your travels. Found in the boreal forests, ... From Google Blog Search: "mammals" |
