Taxonomic rank

The traditional classification of primates (class Mammalia, subclass Theria, infraclass Eutheria, order Primates) has been modified by new classifications such as McKenna and Bell (class Mammalia, subclass Theriformes, infraclass Holotheria) with Theria and Eutheria assigned lower ranks between infraclass and the order Primates. See mammal classification for a discussion. These differences arise because there are only a small number of ranks available and a large number of branching points in the fossil record. Within species further units may be recognised.


Rodents, for example, are a branch of mammals that split off after the end of the period when the clade Dinosauria stopped being the dominant terrestrial vertebrates 66 million years ago. The original population and all its descendants are a clade. The rodent clade corresponds to the order Rodentia, and insects to the class Insecta. These clades include smaller clades, such as chipmunk or ant, each of which consists of even smaller clades. The clade "rodent" is in turn included in the mammal, vertebrate and animal clades.

George Gaylord Simpson

SimpsonGeorge G. SimpsonG. G. Simpson
He was an expert on extinct mammals and their intercontinental migrations. He anticipated such concepts as punctuated equilibrium (in Tempo and mode) and dispelled the myth that the evolution of the horse was a linear process culminating in the modern Equus caballus. He coined the word hypodigm in 1940, and published extensively on the taxonomy of fossil and extant mammals. Simpson was influentially, and incorrectly, opposed to Alfred Wegener's theory of continental drift. He was Professor of Zoology at Columbia University, and Curator of the Department of Geology and Paleontology at the American Museum of Natural History from 1945 to 1959.


glabrousglabrescenthuman hair
In many other mammals, they contain much longer, whisker-like hairs that act as tactile sensors. The eyelash grows at the edges of the eyelid and protects the eye from dirt. The eyelash is to humans, camels, horses, ostriches etc., what whiskers are to cats; they are used to sense when dirt, dust, or any other potentially harmful object is too close to the eye. The eye reflexively closes as a result of this sensation. Hair has its origins in the common ancestor of mammals, the synapsids, about 300 million years ago.


The majority of quadrupeds are vertebrate animals, including mammals such as cattle, dogs and cats, and reptiles such as lizards. Few other animals are quadrupedal, though a few birds like the shoebill sometimes use their wings to right themselves after lunging at prey. Although the words quadruped and tetrapod are both derived from terms meaning "four-footed", they have distinct meanings. A tetrapod is any member of the taxonomic unit Tetrapoda (which is defined by descent from a specific four-limbed ancestor) whereas a quadruped actually uses four limbs for locomotion. Not all tetrapods are quadrupeds and not all quadrupeds are tetrapods.


PalaeoceneLate PaleocenePaleocene epoch
In general, Paleocene mammals retained this small size until near the end of the epoch, and, consequently, early mammal bones are not well preserved in the fossil record, and most of what we know comes from fossil teeth. Multituberculates, a now-extinct rodent-like group not closely related to any modern mammal, were the most successful group of mammals in the Mesozoic, and they reached peak diversity in the early Paleocene. During this time, multituberculate taxa had a wide range of dental complexity, which correlates to a broader range in diet for the group as a whole.


The Proboscidea (from the Greek προβοσκίς and the Latin proboscis) are a taxonomic order of afrotherian mammals containing one living family (Elephantidae) and several extinct families. This order, first described by J. Illiger in 1811, encompasses the trunked mammals. In addition to their enormous size, later proboscideans are distinguished by tusks and long, muscular trunks; these features were less developed or absent in the smaller early proboscideans. Beginning in the mid-Miocene, most members of this order were very large animals. The largest land mammal today is the African elephant weighing up to 10.4 tonnes with a shoulder height of up to 4 m.

Marine mammal

marine mammalssea mammalssea mammal
Sirenians, the sea cows, became aquatic around 40 million years ago. The first appearance of sirenians in the fossil record was during the early Eocene, and by the late Eocene, sirenians had significantly diversified. Inhabitants of rivers, estuaries, and nearshore marine waters, they were able to spread rapidly. The most primitive sirenian, †Prorastomus, was found in Jamaica, unlike other marine mammals which originated from the Old World (such as cetaceans ). The first known quadrupedal sirenian was †Pezosiren from the early Eocene.


gestatinggestategestational period
It is typical for mammals, but also occurs for some non-mammals. Mammals during pregnancy can have one or more gestations at the same time, for example in a multiple birth. The time interval of a gestation is called the gestation period. In human obstetrics, gestational age refers to the fertilization age plus two weeks. This is approximately the duration since the woman's last menstrual period (LMP) began. In mammals, as well as reptiles, pregnancy begins when a zygote (fertilized ovum) implants in the female's uterus and ends once the fetus leaves the uterus.


Rhinoceros horns, unlike those of other horned mammals, (which have a bony core), only consist of keratin, similar to human hair and nails. Rhinoceros horns are used in traditional medicines in parts of Asia, and for dagger handles in Yemen and Oman. Esmond Bradley Martin has reported on the trade for dagger handles in Yemen. In Europe, it was historically believed that rhino horns could purify water and could detect poisoned liquids, and likely as an aphrodisiac and an antidote to poison. The Vietnamese are the biggest consumers of rhino horn, and their demand drives most of the poaching, which has risen to record levels.


Insects, birds and mammals play roles in literature and film, such as in giant bug movies. Animals including insects and mammals feature in mythology and religion. In both Japan and Europe, a butterfly was seen as the personification of a person's soul, while the scarab beetle was sacred in ancient Egypt. Among the mammals, cattle, deer, horses, lions, bats, bears, and wolves are the subjects of myths and worship. The signs of the Western and Chinese zodiacs are based on animals. * Lists of organisms by population Animal attacks. Animal coloration. Ethology. Fauna. List of animal names. Lists of organisms by population. Tree of Life Project.


lungspulmonaryright lung
In mammals and most other vertebrates, two lungs are located near the backbone on either side of the heart. Their function in the respiratory system is to extract oxygen from the atmosphere and transfer it into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere, in a process of gas exchange. Respiration is driven by different muscular systems in different species. Mammals, reptiles and birds use their different muscles to support and foster breathing. In early tetrapods, air was driven into the lungs by the pharyngeal muscles via buccal pumping, a mechanism still seen in amphibians.

Thoracic diaphragm

In birds and mammals, lungs are located above the diaphragm. The presence of an exceptionally well-preserved fossil of Sinosauropteryx, with lungs located beneath the diaphragm as in crocodiles, has been used to argue that dinosaurs could not have sustained an active warm-blooded physiology, or that birds could not have evolved from dinosaurs. An explanation for this (put forward in 1905), is that lungs originated beneath the diaphragm, but as the demands for respiration increased in warm-blooded birds and mammals, natural selection came to favor the parallel evolution of the herniation of the lungs from the abdominal cavity in both lineages. However, birds do not have diaphragms.


craniumcranialhuman skull
Humans may be: ; Mammals ; Birds ; Reptiles Anapsida – no openings. Synapsida – one low opening (beneath the postorbital and squamosal bones). Euryapsida – one high opening (above the postorbital and squamosal bones); euryapsids actually evolved from a diapsid configuration, losing their lower temporal fenestra. Diapsida – two openings. Amniota. Class Synapsida. Order Therapsida. Class Mammaliamammals. (Unranked) Sauropsida – reptiles and birds. Class Reptilia. Subclass Parareptilia. Infraclass Anapsida. Subclass Eureptilia. Infraclass Diapsida. Infraclass Euryapsida. Class Aves – birds. Chondrocranium, a primitive cartilagionous skeletal structure. Endocranium. Epicranium.


Vibrissae grow in various places on most mammals, including all primates except humans. In medicine, the term vibrissae also refers to the thick hairs found inside human nostrils. Vibrissae (derived from the Latin "vibrio" meaning to vibrate) typically grow in groups in different locations on an animal. These groups are relatively well conserved across land mammals, and somewhat less well conserved between land and marine mammals (though commonalities are certainly present). Species-specific differences are also found.

Parental care

carecaresoffspring provisioning
There is maternal care in all species of mammals. 95% species exhibit female-only care. In the remaining 5% of species, there is biparental care. There are no known cases of male-only care. Higher mammals (excluding the monotremes, namely the echidna and the platypus) share two major adaptations for care of their young, namely gestation (development of the embryo inside the mother's body, followed by live birth) and production of milk. Many mammals exhibit further parental care, including building a nest, digging a burrow, or feeding and guarding their young, often for a prolonged period.

Estrous cycle

Thus in North American English, a mammal may be described as "in estrus" when it is in that particular part of the estrous cycle. A four-phase terminology is used in reference to animals with estrous cycles. One or several follicles of the ovary start to grow. Their number is species specific. Typically this phase can last as little as one day or as long as three weeks, depending on the species. Under the influence of estrogen the lining in the uterus (endometrium) starts to develop. Some animals may experience vaginal secretions that could be bloody.

R/K selection theory

Organisms that exhibit r-selected traits can range from bacteria and diatoms, to insects and grasses, to various semelparous cephalopods and small mammals, particularly rodents. As with K-selection, below, the r/K paradigm (Differential K theory) has controversially been associated with human behavior and separately evolved populations. By contrast, K-selected species display traits associated with living at densities close to carrying capacity and typically are strong competitors in such crowded niches that invest more heavily in fewer offspring, each of which has a relatively high probability of surviving to adulthood (i.e., low r, high K).

Steller's sea cow

Hydrodamalis gigasSteller sea cow(Steller's) sea cow
Steller's sea cows grew to be 8 to 9 m long as adults, much larger than extant sirenians. Georg Steller's writings contain two contradictory estimates of weight: 4 and 24.3 MT. The true value is estimated to fall between these figures, at about 8 - 10 MT. This size made the sea cow one of the largest mammals of the Holocene epoch, along with whales. The sea cow's large size was likely an adaptation to reduce its surface area-to-volume ratio and conserve heat. Unlike other sirenians, Steller's sea cow was positively buoyant, meaning that it was unable to completely submerge.


aardvarksOrycteropus aferant bear
Along with the sirenians, hyraxes, elephants, and their extinct relatives, these animals form the superorder Afrotheria. Studies of the brain have shown the similarities with Condylarthra, and given the clade's status as a wastebasket taxon it may mean some species traditionally classified as "condylarths" are actually stem-aardvarks. Based on fossils, Bryan Patterson has concluded that early relatives of the aardvark appeared in Africa around the end of the Paleocene. The ptolemaiidans, a mysterious clade of mammals with uncertain affinities, may actually be stem-aardvarks, either as a sister clade to Tubulidentata or as a grade leading to true tubulidentates.


placentalplacental mammalplacental mammals
Placentalia is one of the three extant subdivisions of the class of animals Mammalia; the other two are Monotremata and Marsupialia. The placentals are partly distinguished from other mammals in that the fetus is carried in the uterus of its mother to a relatively late stage of development. The name is something of a misnomer considering that marsupials also nourish their fetuses via a placenta, though for a relatively briefer period, giving birth to less developed young who are then kept for a period in the mother’s pouch.


Protosirenidae is an extinct primitive family of the order Sirenia. The protosirenidae is thought to have been an amphibious quadruped, meaning that it spent its time both on land and in the water and had four legs. * Protosiren at The Paleobiology Database. Dugongidae. Evolution of sirenians. Manatee.

West Indian manatee

Florida manateeTrichechus manatusAntillean manatee
The West Indian manatee (Trichechus manatus) or "sea cow", also known as North American manatee, is the largest surviving member of the aquatic mammal order Sirenia (which also includes the dugong and the extinct Steller's sea cow). The West Indian manatee is a species distinct from the Amazonian manatee (''T. inunguis) and the African manatee (T. senegalensis''). Based on genetic and morphological studies, the West Indian manatee is divided into two subspecies, the Florida manatee (''T. m. latirostris) and the Antillean or Caribbean manatee (T. m. manatus'').


The Desmostylia (from Greek δεσμά desma, "bundle", and στῦλος stylos, "pillar") are an extinct order of aquatic mammals that existed from the early Oligocene (Rupelian) to the late Miocene (Tortonian). Desmostylians are the only known extinct order of marine mammals (Thalassocnus, a genus of marine sloths, became extinct more recently). The Desmostylia, together with Sirenia and Proboscidea (and possibly Embrithopoda), have traditionally been assigned to the afrotherian clade Tethytheria, a group named after the paleoocean Tethys around which they originally evolved.


O'Brien (Edited by Morris Goodman). 2002 Placental mammal diversification and the Cretaceous-Tertiary boundary. Wildman D.E.; Chen C.; Erez O.; Grossman L.I.; Goodman M.; Romero R. 2006. Evolution of the mammalian placenta revealed by phylogenetic analysis" PNAS 103 (9) 3203–3208. Nikolaev, S., Montoya-Burgos, J.I., Margulies, E.H., Rougemont, J., Nyffeler, B., Antonarakis, S.E. 2007. Early history of mammals is elucidated with the ENCODE multiple species sequencing data" PLoS Genet 3:e2,. Gennady Churakov, Jan Ole Kriegs, Robert Baertsch, Anja Zemann, Jürgen Brosius, Jürgen Schmitz. 2008. Mosaic retroposon insertion patterns in placental mammals.