Nawraj: improved references further and fixed typos

2026-03-23T01:29:02Z

improved references further and fixed typos

WikiDwarfBOT: robot: Trimming article to decrease server load

2022-09-26T04:11:26Z

robot: Trimming article to decrease server load

← Older revision	Revision as of 09:41, 26 September 2022
(No difference)

WikiDwarfBOT: robot: Trimming article to decrease server load

2022-08-26T04:11:26Z

robot: Trimming article to decrease server load

Show changes

UpdateBot: robot: Update article (please report if you notice any mistake or error in this edit)

2022-06-30T02:18:49Z

robot: Update article (please report if you notice any mistake or error in this edit)

Show changes

ImportMaster: robot: Creating new article from Special:WantedPages

2021-11-07T12:32:01Z

robot: Creating new article from Special:WantedPages

New page

{{Automatic taxobox
| name = Mammalia
| fossil_range = 225–0 mya (Kemp)<ref name=Kemp/> <br/>or 167–0 mya (Rowe)<ref name=Rowe>Rowe T. 1988. Definition, diagnosis, and origin of Mammalia. ''Journal of Vertebrate Paleontology'' '''8''' (3): 241–264.</ref>
|image = <imagemap>
File:Mammal Diversity 2021.jpg|300px

rect 0 0 176 125 [[common vampire bat]]
rect 0 120 176 240 [[Tasmanian devil]]
rect 0 240 176 380 [[fox squirrel]]
rect 0 380 176 500 [[platypus]]
rect 0 500 176 600 [[humpback whale]]
rect 0 760 176 620 [[giant armadillo]]

rect 355 0 176 125 [[Virginia opossum]]
rect 355 120 176 240 [[human]]
rect 355 240 176 380 [[tree pangolin]]
rect 355 380 176 500 [[colugo]]
rect 355 500 176 600 [[star nosed mole]]
rect 355 760 176 620 [[plains zebra]]

rect 530 0 350 125 [[eastern grey kangaroo]]
rect 530 120 350 240 [[northern elephant seal]]
rect 530 240 350 380 [[African elephant]]
rect 530 380 350 500 [[reindeer]]
rect 530 500 350 600 [[giant panda]]
rect 530 760 350 620 [[black and rufous elephant shrew]]
</imagemap>
| display_parents = 3
| taxon = Mammalia
| authority = [[Carl Linnaeus|Linnaeus]], 1758
| subdivision_ranks = Living subgroups
| subdivision =
*Subclass [[Prototheria]]
**Infraclass [[Australosphenida]]
***Order [[Monotreme|Monotremata]]
*Subclass [[Theria]]
**Infraclass [[Metatheria]]
**Infraclass [[Eutheria]]
}}

The [[class (biology)|class]] '''Mammalia''' (from [[Latin]] {{lang|la|mamma}}, 'breast') are a group of [[vertebrate]] [[animal]]s.<ref>Szalay F.S. 1999. Classification of mammals above the species level: Review. ''Journal of Vertebrate Paleontology'' '''19''' (1): 191–195. [[doi:10.1080/02724634.1999.10011133]]. [[JSTOR]] 4523980.</ref> They have [[fur]] or [[hair]] and a very precise kind of [[homoiothermy|temperature regulation]].

With the exception of the [[monotreme]]s, all mammals bear live young. Unlike other [[Vertebrate|vertebrates]], they are the only animals that produce milk for the young through their mammary glands. Parental care of the young is universal among mammals, sometimes for extended periods.

Mammals became the dominant land animals after non-bird [[dinosaurs]] were eliminated. Recent work helped to explain their success: [[epigenetics]] seems to have started in early mammals.<ref>Butler 2009. ''Journal of Assisted Reproduction and Genetics''. p477–486.</ref>

==Main characteristics==
===Reproductive cycle===
Most [[marsupial]] and [[eutherian]] mammals have a reproductive cycle known as the [[oestrous cycle]] (U.S: estrous cycle). Females are sexually active only during the oestrous stage, when they are 'on heat' for a few days each month. If an [[ovum]] is not fertilized, the [[endometrium]] ([[uterus]] lining) is resorbed. Oestrus cycles may occur once or twice a year, or many times a year. Each group of mammals has its own frequency.

[[Human]]s and [[primate]]s, are quite different. They have a [[menstrual cycle]]. In this case, females are sexually receptive at any time, but only fertile when an ovum is released from an ovary. In this case, the endometrium (if not needed for an fertilised egg) is discarded. The endometrium is shed, and takes with it a certain amount of blood. In this system, eggs are released from the ovaries mostly in the middle of the cycle, away from the menstrual period. This [[ovulation]] is 'concealed', meaning, it is not obvious when it occurs. This process, so it is thought, tends to keep the male and female together, which is unusual in mammals with the oestrous cycle.

===Skeleton===
One [[diagnosis|diagnostic]] feature of mammals is the lower [[jaw]]. Unlike earlier forms, it is a single bone, the [[dentary]]. This is one feature which can be seen in fossils, or at least those which are complete enough to have the lower jaw. Another diagnostic feature is the [[ear ossicles]]. Mammals have three little bones in their inner ear. These ear ossicles are bones which were, long ago, part of the lower jaw in early proto-mammals.

There are quite a number of other features in the skull and limbs, so that it is usually possible to identify and describe a mammal from its skeleton alone, or even a partial skeleton.

===Neocortex and behavior===
Another diagnostic feature is the [[Cerebral cortex#Neocortex|neocortex]] of the [[Vertebrate brain|brain]], which no other vertebrate has. This is involved in the kind of flexible [[behavior]] and [[learning]] typical of mammals. Reptiles and birds have much of their behavior controlled by "inherited behavior chains", which roughly translates as "[[instinct]]s". Almost all animals can do some learning, but mammals do far more than other vertebrates. Their behavior is much more flexible than [[lizards]], for example, and that is made possible by their neocortex.

Other things in the life of mammals seem to be connected with this flexibility and learning. [[Play (activity)|Play]] is a kind of early learning period in which, according to one theory,<ref>Burghardt, Gordon M. 2006. ''The genesis of animal play: testing the limits''. MIT Press, p11. {{ISBN|0-262-02543-4}}</ref> mammals develop skills which they will need in life. All mammalian young play, and this is very obvious in the more intelligent mammals ([[primate]]s, [[cats]]).

The [[emotions]] of mammals are very noticeable, and rather similar to ours. It is possible, and quite common, for humans to have a friendly relationship with another mammal. It is quite impossible for a human to have any kind of relationship with a snake or a [[gecko]] (for example). This is because the reptile simply does not have the same basic emotions as a human.

===Other items===
There are about 50 characters which are typical of mammals: some of the most important are discussed above. A few more examples will make it clear that mammals are very different from reptiles and birds:
*[[Sweat]] glands
*Tooth replacement: two sets, and no continuous replacement. Enamel on the tooth surface. Reptile teeth all alike; mammal [[teeth]] follow a pattern ([[incisor]]s, [[canine]]s, [[premolar]]s and [[molar]]s).
*Occipital condyles. Two knobs at the base of the skull fit into the topmost neck [[vertebra]]; most [[tetrapods]] have only one such knob.
*With the exception of the five monotreme species, all other mammals have an outlet for food waste which is separate from the [[urinogenital]] outlet. Monotremes, reptiles and birds have a common [[cloaca]] at the rear.
*Mammals [[excretion|excrete]] [[urea]]; reptiles and birds excrete [[uric acid]].
*[[Colour vision]] is defective or absent in almost all mammals (primates are the exception, but we know their colour vision re-evolved from ancestors which lacked it).
*In reptiles and birds the blood vessel which carries oxygenated blood from the left ventricle of the heart is on the right side of the body; but in mammals it is on the left side.<ref>Kermack D.M. & K.A. 1984. ''The evolution of mammalian characters''. London: Croom Helm, p6. {{ISBN|0-7099-1534-9}}</ref>
*There are many features of the skeleton that mammals share
**Their neck almost always has seven vertebrae, no matter how long it is.
**Their lower jaw is made of just a single bone on each side, the [[dentary]].
**Their [[inner ear]] has three tiny bones, the [[ossicles]]: malleus, incus and stapes.
*One extraordinary thing has come to light: [[epigenetics]] has evolved in mammals, and is (to present knowledge) unique to mammals. The implications of this, if true, are not known.

In the language of [[cladistics]], the 50 unique characters are [[apomorphy|apomorphies]] which prove that mammals are a [[clade]] descended from a [[common ancestor]].<ref name=Kemp>Kemp T.S. 2005. ''The origin and evolution of mammals''. Oxford University Press, p2. {{ISBN|0-19-850761-5}}</ref>

==Main groups==
All mammals feed milk to their young, and protect and look after them.

The vast majority of mammal species give [[birth]] to live young, these are the [[placenta]]l mammals, most of which are classified as [[Eutheria]] and a small number are classified as [[marsupials]].<ref>Vaughan T.A; Ryan J.M. & Czaplewski N.J. 2013. Classification of Mammals in ''Mammalogy'' (6 ed). Jones and Bartlett Learning. ISBN 978-1-284-03209-3</ref>

Marsupials are mammals with pouches to carry young in, like the [[kangaroo]].

There are only five species (the [[monotreme]] mammals) that lay [[Cleidoic egg|eggs]], the duck-billed [[platypus]] ''Ornithorhynchus'', and four species of spiny anteater ''[[Echidna]]''. The [[monotreme]]s are confined to [[Australia]] and [[New Guinea]], and are the sole survivors of an earlier group of mammals.

==Modes of life==
By number of species, mammals (with 5488 species),<ref>{{cite web | title=Initiatives | work=The IUCN Red List of threatened species | date=April 2010 | publisher=IUCN | url=http://www.iucnredlist.org/initiatives}}</ref> are not the most successful vertebrates. Birds, with about 10,000 species have nearly twice as many,<ref>{{Cite book|title=The Clements checklist of birds of the world |first=James F. |last=Clements |edition=6th |location=Ithaca |publisher=Cornell University Press |year=2007 |isbn=978-0-8014-4501-9}}</ref><ref>{{Cite book|last=Gill |first=Frank |year=2006 |title=Birds of the world: recommended English names |url=https://archive.org/details/birdsofworldreco0000gill |location=Princeton |publisher=Princeton University Press |isbn=978-0-691-12827-6}}</ref> and reptiles have just as many as birds.<ref>[http://www.reptile-database.org/ The Reptile Database]</ref> Fish have even more species. There are 27,000 species of fish, of which nearly 26,000 are bony fish.<ref>Nelson, Joseph S. 2006. ''Fishes of the World''. 4th ed, John Wiley. {{ISBN|9780471756446}} [https://web.archive.org/web/20130305052159/http://www.somas.stonybrook.edu/~conover/Textbooks/Fishes%20of%20the%20World,%204th%20ed.%20Joseph%20S.%20Nelson.pdf]</ref>

Despite this, many zoologists do regard mammals as a successful group of animals. One reason is that they are successful in all [[habitats]] on Earth. In the air, in the water, in [[forests]], in the colder regions of the world, and above all on [[grasslands]], where they are outstandingly successful.

In the air, the [[bats]] ([[Chiroptera]]) are the mammalian order with the most species. They 'own' the nighttime, since birds are largely diurnal (daytime) animals. Bats are hugely successful, mostly as nighttime predators of insects.

Seagoing mammals, the [[Cetacea]] and the [[pinniped]]s, are very successful and significant [[predator]]s. This includes the [[whale]]s, [[Pinniped|seals]], [[walrus]], [[dolphin]]s and others.

The terrestrial mammals are fewer in number of species than [[lizards]], but they are huge in individual numbers, and far more important in the life of the terrestrial [[biome]]s. Their ability to move from place to place and adapt has made them a most effective group. Many mammals live in cold places. These mammals have thick hair or [[blubber]] to keep them warm. Others may live in rainforests. On land the [[rodent]]s (rats, mice) are hugely successful, more common in numbers than any other mammals. Large mammals on land have been hunted to [[extinct]]ion in some parts of the world, but the ones which remain are now better protected.

Last, but certainly not least, are the [[primate]]s. Their natural [[habitat]], with few exceptions, are the [[forest]]s. Most live in the trees, with hands that grasp, good [[colour vision]], and [[intelligence]]. In the [[Pliocene]] period some moved out onto the [[savanna]]s as [[grassland]] replaced forests. [[human race|Mankind]] is the result of this shift into the savannas.

==Taxonomy==
The evolutionary relationships among land vertebrates is as follows:
*[[Tetrapoda]] (land vertebrates)
**[[Amphibia]] (lay eggs in water)
**[[Amniota]] (lay [[cleidoic egg]]s)
***[[Sauropsida]] (all true '[[reptile]]s')
***[[Synapsida]] (all '[[mammal-like reptile|mammal-like amniotes]]')
****[[Pelycosauria]]
****[[Therapsida]] (in particular, the [[Cynodontia]])
*****'''Mammalia''' (bear live young; milk; raise their young etc.)

This sort of classification is not traditional, but it does reflect our knowledge of [[palaeontology]] and [[evolution]].<ref>Clack Jennifer A. 2012. ''Gaining Ground: the origin and early evolution of tetrapods''. 2nd ed, Indiana University Press, Bloomington IN. {{ISBN|978-0-253-35675-8}}</ref>

===Standardized textbook classification===
A somewhat standardized classification system has been adopted by most current [[mammalogy]] classroom textbooks. It is based on living animals. The following taxonomy of extant and recently extinct mammals is from Vaughan et al. 2000.<ref>Vaughan, Terry A., James M. Ryan, and Nicholas J. Capzaplewski. 2000. ''Mammalogy'': 4th ed, Saunders. {{ISBN|0-03-025034-X}} Brooks Cole, 1999.</ref>

'''Class Mammalia'''
*'''Subclass [[Prototheria]]''': monotremes: [[platypus]]es and [[echidna]]s
*'''Subclass [[Theria]]''': live-bearing mammals
**Infraclass [[Metatheria]]: marsupials
**Infraclass [[Eutheria]]: placentals

===List of living orders===
[[File:Mammal species pie chart.png|thumb|300px|Over ¾ of mammal species are in the orders [[Rodent]]ia (blue), [[Chiroptera]] (red), [[Soricomorpha]] (yellow) and [[Primate]]s (green).]]
Mammals can be divided in a number of orders:
* [[Monotreme]]s (monotremata)
* [[Marsupial]]s (marsupialia)
* [[Eutheria]]
** Superorder [[Xenarthra]]
*** Order [[Pilosa]]
*** Order [[Cingulata]]
** Superorder [[Afrotheria]]
*** Order [[Proboscidea]]
** Superorder [[Laurasiatheria]]
*** [[Insectivora]] (no longer used)
*** Order [[Eulipotyphla]]
*** Order [[Chiroptera]]
*** Order [[Carnivora]]
*** Order [[Perissodactyla]]
*** Order [[Artiodactyla]]
*** Order [[Cetacea]]
** Superorder [[Euarchontoglires]]
*** Order [[Rodentia]]
*** Order [[Lagomorpha]]
*** Order [[Primate]]s

==Debate on the meaning of "mammalia"==
Because two quite different dates are given in the taxobox, an explanation is needed. Rowe defines mammals as "the taxon originating with the most recent common ancestor of extant (living) [[Monotremata]] and [[Theria]]". That puts the emphasis heavily on living mammals, where, as Rowe points out, the database of characters is extensive.<ref name=Rowe/>

Kemp explains the problem with that approach: "If the definition of a mammal is based rigorously upon possession of all the characters of living mammals, then some fossil forms that are extremely mammalian in anatomy... are excluded".<ref name=Kemp/>

"An altogether different perspective on defining Mammalia is based on traditional palaeobiological practice. An arbitrary decision is made about which characters to select as defining characters... Characters deemed appropriate are those reflecting the... fundamental mammalian biology. The essence of mammalian life is to be found in their [[endothermy|endothermic temperature physiology]], greatly enlarged [[brain]], [[dentition]] capable of chewing food, highly agile, energetic locomotion, and so on. The organisms that achieved this grade of overall organisation are deemed to be Mammalia... Around the end of the [[Triassic]] period, about 205 mya, a number of fossils are found of very small animals that have [most] of the skeletal characters of modern mammals".<ref name=Kemp/>

This difference in outlook explains the difference in the two dates given in the taxobox.

==Gallery==
<gallery>
File:Ursus maritinus.jpg|[[Polar bear]]
File:Big-eared-townsend-fledermaus.jpg|[[Bat]]
File:Camel seitlich trabend.jpg|[[Camel]]
File:Manatee with calf.PD.jpg|[[Manatee]]
</gallery>

==See also==
* [[Mammalia (taxonomy)]]

==References==
{{Reflist}}
{{wikispecies|Mammalia}}
{{commonscat|Mammals}}

{{vertebrates}}

[[Category:Mammals| ]]

Mammal - Revision history

Nawraj: improved references further and fixed typos

WikiDwarfBOT: robot: Trimming article to decrease server load

WikiDwarfBOT: robot: Trimming article to decrease server load

UpdateBot: robot: Update article (please report if you notice any mistake or error in this edit)

ImportMaster: robot: Creating new article from Special:WantedPages