Temporal range: 225–0 Ma (Kemp) or 167–0 Ma (Rowe) See discussion of dates in text
Mammals (class Mammalia // from Latin mamma "breast") are a clade of endothermic amniotes distinguished from reptiles and birds by the possession of a neocortex (a region of the brain), hair, three middle ear bones and mammary glands.
Mammals include the largest animals on the planet, the great whales, as well as some of the most intelligent, such as elephants, primates and cetaceans. The basic body type is a terrestrial quadruped, but some mammals are adapted for life at sea, in the air, in trees, underground or on two legs. The largest group of mammals, the placentals, have a placenta, which enables the feeding of the fetus during gestation.
Mammals range in size from the 30–40 mm (1.2–1.6 in) bumblebee bat to the 33-meter (108 ft) blue whale. With the exception of the five species of monotreme (egg-laying mammals), all modern mammals give birth to live young. Most mammals, including the six most species-rich orders, belong to the placental group. The three largest orders in number of species are Rodentia: mice, rats, porcupines, beavers, capybaras and other gnawing mammals; Chiroptera: bats; and Soricomorpha: shrews, moles and solenodons. The next three biggest orders, depending on the biological classification scheme used, are the Primates including the great apes and monkeys; the Cetartiodactyla including whales and even-toed ungulates; and the Carnivora which includes cats, dogs, weasels, bears and seals.
The word "mammal" is modern, from the scientific name Mammalia, coined by Carl Linnaeus in 1758, derived from the Latin mamma ("teat, pap"). All female mammals nurse their young with milk, which is secreted from special glands, the mammary glands. According to Mammal Species of the World, 5,416 species were known in 2006. These were grouped in 1,229 genera, 153 families and 29 orders. In 2008 the International Union for Conservation of Nature (IUCN) completed a five-year, 1,700-scientist Global Mammal Assessment for its IUCN Red List, which counted 5,488 species. In some classifications, extant mammals are divided into two subclasses: the Prototheria, that is, the order Monotremata; and the Theria, or the infraclasses Metatheria and Eutheria. The marsupials constitute the crown group of the Metatheria, and include all living metatherians as well as many extinct ones; the placentals are the crown group of the Eutheria. While mammal classification at the family level has been relatively stable, several contending classifications regarding the higher levels—subclass, infraclass and order, especially of the marsupials—appear in contemporaneous literature. Much of the changes reflect the advances of cladistic analysis and molecular genetics. Findings from molecular genetics, for example, have prompted adopting new groups, such as the Afrotheria, and abandoning traditional groups, such as the Insectivora.
The early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that produced the non-mammalian Dimetrodon. At the end of the Carboniferous period, this group diverged from the sauropsid line that led to today's reptiles and birds. The line following the stem group Sphenacodontia split-off several diverse groups of non-mammalian synapsids—sometimes referred to as mammal-like reptiles—before giving rise to the proto-mammals (Therapsida) in the early Mesozoic era. The modern mammalian orders arose in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs, and have been among the dominant terrestrial animal groups from 66 million years ago to the present.
- 1 Classification
- 2 Evolutionary history
- 3 Anatomy and morphology
- 4 Behavior
- 5 Locomotion
- 6 Hybrids
- 7 See also
- 8 References
- 9 Further reading
- 10 External links
Mammal classification has been through several iterations since Carl Linnaeus initially defined the class. No classification system is universally accepted; McKenna & Bell (1997) and Wilson & Reader (2005) provide useful recent compendiums. George Gaylord Simpson's "Principles of Classification and a Classification of Mammals" (AMNH Bulletin v. 85, 1945) provides systematics of mammal origins and relationships that were universally taught until the end of the 20th century. Since Simpson's classification, the paleontological record has been recalibrated, and the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself, partly through the new concept of cladistics. Though field work gradually made Simpson's classification outdated, it remained the closest thing to an official classification of mammals.
The word "mammal" is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from the Latin mamma ("teat, pap"). In an influential 1988 paper, Timothy Rowe defined Mammalia phylogenetically as the crown group of mammals, the clade consisting of the most recent common ancestor of living monotremes (echidnas and platypuses) and therian mammals (marsupials and placentals) and all descendants of that ancestor. Since this ancestor lived in the Jurassic period, Rowe's definition excludes all animals from the earlier Triassic, despite the fact that Triassic fossils in the Haramiyida have been referred to the Mammalia since the mid-19th century. If Mammalia is considered as the crown group, its origin can be roughly dated as the first known appearance of animals more closely related to some extant mammals than to others. Ambondro is more closely related to monotremes than to therian mammals while Amphilestes and Amphitherium are more closely related to the therians; as fossils of all three genera are dated about in the Middle Jurassic, this is a reasonable estimate for the appearance of the crown group.
T. S. Kemp has provided a more traditional definition: "synapsids that possess a dentary–squamosal jaw articulation and occlusion between upper and lower molars with a transverse component to the movement" or, equivalently in Kemp's view, the clade originating with the last common ancestor of Sinoconodon and living mammals. The earliest known synapsid satisfying Kemp's definitions is Tikitherium, dated , so the appearance of mammals in this broader sense can be given this Late Triassic date.
In 1997, the mammals were comprehensively revised by Malcolm C. McKenna and Susan K. Bell, which has resulted in the McKenna/Bell classification. Their 1997 book, Classification of Mammals above the Species Level, is a comprehensive work on the systematics, relationships and occurrences of all mammal taxa, living and extinct, down through the rank of genus, though molecular genetic data challenge several of the higher level groupings. The authors worked together as paleontologists at the American Museum of Natural History, New York. McKenna inherited the project from Simpson and, with Bell, constructed a completely updated hierarchical system, covering living and extinct taxa that reflects the historical genealogy of Mammalia.
- Subclass Prototheria: monotremes: echidnas and the platypus
- Subclass Theriiformes: live-bearing mammals and their prehistoric relatives
- Infraclass †Allotheria: multituberculates
- Infraclass †Eutriconodonta: eutriconodonts
- Infraclass Holotheria: modern live-bearing mammals and their prehistoric relatives
- Superlegion †Kuehneotheria
- Supercohort Theria: live-bearing mammals
- Cohort Marsupialia: marsupials
- Cohort Placentalia: placentals
- Magnorder Xenarthra: xenarthrans
- Magnorder Epitheria: epitheres
- Superorder Anagalida: lagomorphs, rodents and elephant shrews
- Superorder Ferae: carnivorans, pangolins, †creodonts and relatives
- Superorder Lipotyphla: insectivorans
- Superorder Archonta: bats, primates, colugos and treeshrews
- Superorder Ungulata: ungulates
Molecular classification of placentals
Molecular studies based on DNA analysis have suggested new relationships among mammal families over the last few years. Most of these findings have been independently validated by retrotransposon presence/absence data. Classification systems based on molecular studies reveal three major groups or lineages of placental mammals- Afrotheria, Xenarthra and Boreoeutheria- which diverged in the Cretaceous. The relationships between these three lineages is contentious, and all three possible different hypotheses have been proposed with respect to which group is basal. These hypotheses are Atlantogenata (basal Boreoeutheria), Epitheria (basal Xenarthra) and Exafroplacentalia (basal Afrotheria). Boreoeutheria in turn contains two major lineages- Euarchontoglires and Laurasiatheria.
Estimates for the divergence times between these three placental groups range from 105 to 120 million years ago, depending on type of DNA (such as nuclear or mitochondrial) and varying interpretations of paleogeographic data.
Group I: Afrotheria
- Clade Afroinsectiphilia
- Clade Paenungulata
Group II: Xenarthra
- Order Pilosa: sloths and anteaters (neotropical)
- Order Cingulata: armadillos and extinct relatives (Americas)
Group III: Boreoeutheria
- Clade: Euarchontoglires (Supraprimates)
- Superorder Euarchonta
- Superorder Glires
- Clade Laurasiatheria
- Order Eulipotyphla: shrews, hedgehogs, moles, solenodons
- Clade Ferungulata
- Clade Cetartiodactyla
- Clade Pegasoferae
- Order Chiroptera: bats (cosmopolitan)
- Clade Zooamata
Most mammals, including the six most species-rich orders, belong to the placental group. The three largest orders in numbers of species are Rodentia: mice, rats, porcupines, beavers, capybaras and other gnawing mammals; Chiroptera: bats; and Soricomorpha: shrews, moles and solenodons. The next three biggest orders, depending on the biological classification scheme used, are the Primates including the great apes and monkeys; the Cetartiodactyla including whales and even-toed ungulates; and the Carnivora which includes cats, dogs, weasels, bears and seals. According to Mammal Species of the World, 5,416 species were known in 2006. These were grouped in 1,229 genera, 153 families and 29 orders. In 2008 the International Union for Conservation of Nature (IUCN) completed a five-year, 1,700-scientist Global Mammal Assessment for its IUCN Red List, which counted 5,488 species.
Synapsida, a clade that contains mammals and their extinct relatives, originated during the Pennsylvanian subperiod, when they split from reptilian and avian lineages. Crown group mammals evolved from earlier mammaliaforms during the Early Jurassic.
The cladogram following takes Mammalia to be the crown group.
A cladogram compiled by Mikko Haaramo based on individual cladograms of After Rowe 1988; Luo, Crompton & Sun 2001; Luo, Cifelli & Kielan-Jaworowska 2001, Luo, Kielan-Jaworowska & Cifelli 2002, Kielan-Jaworowska, Cifelli & Luo 2004 and Luo & Wible 2005.
Evolution from amniotes
The first fully terrestrial vertebrates were amniotes. Like their amphibious tetrapod predecessors, they had lungs and limbs. Amniotic eggs, however, have internal membranes that allow the developing embryo to breathe but keep water in. Hence, amniotes can lay eggs on dry land, while amphibians generally need to lay their eggs in water.
The first amniotes apparently arose in the Late Carboniferous. They descended from earlier reptiliomorph amphibious tetrapods, which lived on land that was already inhabited by insects and other invertebrates as well as ferns, mosses and other plants. Within a few million years, two important amniote lineages became distinct: the synapsids, which would later include the common ancestor of the mammals; and the sauropsids, which now include turtles, lizards, snakes, crocodilians, dinosaurs and birds. Synapsids have a single hole (temporal fenestra) low on each side of the skull. One synapsid group, the pelycosaurs, included the largest and fiercest animals of the early Permian. Nonmammalian synapsids are sometimes called "mammal-like reptiles".
Therapsids descended from pelycosaurs in the Middle Permian, about 265 million years ago, and became the dominant land vertebrates. They differ from basal eupelycosaurs in several features of the skull and jaws, including: larger skulls and incisors which are equal in size in therapsids, but not for eupelycosaurs. The therapsid lineage leading to mammals went through a series of stages, beginning with animals that were very similar to their pelycosaur ancestors and ending with probainognathian cynodonts, some of which could easily be mistaken for mammals. Those stages were characterized by:
- The gradual development of a bony secondary palate.
- Progression towards an erect limb posture, which would increase the animals' stamina by avoiding Carrier's constraint. But this process was slow and erratic: for example, all herbivorous nonmammaliaform therapsids retained sprawling limbs (some late forms may have had semierect hind limbs); Permian carnivorous therapsids had sprawling forelimbs, and some late Permian ones also had semisprawling hindlimbs. In fact, modern monotremes still have semisprawling limbs.
- The dentary gradually became the main bone of the lower jaw which, by the Triassic, progressed towards the fully mammalian jaw (the lower consisting only of the dentary) and middle ear (which is constructed by the bones that were previously used to construct the jaws of reptiles).
The Permian–Triassic extinction event, which was a prolonged event due to the accumulation of several extinction pulses, ended the dominance of carnivores therapsids. In the early Triassic, most medium to large land carnivore niches were taken over by archosaurs which, over an extended period of time (35 million years), came to include the crocodylomorphs, the pterosaurs and the dinosaurs; however, large cynodonts like Trucidocynodon and traversodontids still occupied large sized carnivorous and herbivorous niches respectively. By the Jurassic, the dinosaurs had come to dominate the large terrestrial herbivore niches as well.
The first mammals (in Kemp's sense) appeared in the Late Triassic epoch (about 225 million years ago), 40 million years after the first therapsids. They expanded out of their nocturnal insectivore niche from the mid-Jurassic onwards; The Jurassic Castorocauda, for example, had adaptations for swimming, digging and catching fish. Most, if not all, are thought to have remained nocturnal (the Nocturnal bottleneck), accounting for much of the typical mammalian traits. The majority of the mammal species that existed in the Mesozoic Era were multituberculates, eutriconodonts and spalacotheriids. The earliest known metatherian is Sinodelphys, found in 125 million-year-old Early Cretaceous shale in China's northeastern Liaoning Province. The fossil is nearly complete and includes tufts of fur and imprints of soft tissues.
The oldest known fossil among the Eutheria ("true beasts") is the small shrewlike Juramaia sinensis, or "Jurassic mother from China", dated to 160 million years ago in the late Jurassic. A later eutherian, Eomaia, dated to 125 million years ago in the early Cretaceous, possessed some features in common with the marsupials but not with the placentals, evidence that these features were present in the last common ancestor of the two groups but were later lost in the placental lineage. In particular, the epipubic bones extend forwards from the pelvis. These are not found in any modern placental, but they are found in marsupials, monotremes, nontherian mammals and Ukhaatherium, an early Cretaceous animal in the eutherian order Asioryctitheria. This also applies to the multituberculates. They are apparently an ancestral feature, which subsequently disappeared in the placental lineage. These epipubic bones seem to function by stiffening the muscles during locomotion, reducing the amount of space being presented, which placentals require to contain their fetus during gestation periods. A narrow pelvic outlet indicates that the young were very small at birth and therefore pregnancy was short, as in modern marsupials. This suggests that the placenta was a later development.
The earliest known monotreme was Teinolophos, which lived about 120 million years ago in Australia. Monotremes have some features which may be inherited from the original amniotes such as the same orifice to urinate, defecate and reproduce (cloaca) – as lizards and birds also do – and they lay eggs which are leathery and uncalcified.
Earliest appearances of features
Hadrocodium, whose fossils date from approximately 195 million years ago, in the early Jurassic, provides the first clear evidence of a jaw joint formed solely by the squamosal and dentary bones; there is no space in the jaw for the articular, a bone involved in the jaws of all early synapsids.
The earliest clear evidence of hair or fur is in fossils of Castorocauda, from 164 million years ago in the mid-Jurassic. In the 1950s, it was suggested that the foramina (passages) in the maxillae and premaxillae (bones in the front of the upper jaw) of cynodonts were channels which supplied blood vessels and nerves to vibrissae (whiskers) and so were evidence of hair or fur; it was soon pointed out, however, that foramina do not necessarily show that an animal had vibrissae, as the modern lizard Tupinambis has foramina that are almost identical to those found in the nonmammalian cynodont Thrinaxodon. Popular sources, nevertheless, continue to attribute whiskers to Thrinaxodon. Studies on Permian coprolites suggest that non-mammalian synapsids of the epoch already had fur, setting the evolution of hairs possibly as far back as dicynodonts.
When endothermy first appeared in the evolution of mammals is uncertain, though it is generally agreed to have first evolved in non-mammalian therapsids. Modern monotremes have lower body temperatures and more variable metabolic rates than marsupials and placentals, but there is evidence that some of their ancestors, perhaps including ancestors of the therians, may have had body temperatures like those of modern therians. Likewise, some modern therians like afrotheres and xenarthrans have secondarily developed lower body temperatures.
The evolution of erect limbs in mammals is incomplete — living and fossil monotremes have sprawling limbs. The parasagittal (nonsprawling) limb posture appeared sometime in the late Jurassic or early Cretaceous; it is found in the eutherian Eomaia and the metatherian Sinodelphys, both dated to 125 million years ago. Epipubic bones, a feature that strongly influenced the reproduction of most mammal clades, are first found in Tritylodontidae, suggesting that it is a synapomorphy between them and mammaliformes. They are omnipresent in non-placental mammaliformes, though Megazostrodon and Erythrotherium appear to have lacked them.
Rise of the mammals
Mammals took over the medium- to large-sized ecological niches in the Cenozoic, after the Cretaceous–Paleogene extinction event emptied ecological space once filled by non-avian dinosaurs and other groups of reptiles. Then mammals diversified very quickly; both birds and mammals show an exponential rise in diversity. For example, the earliest known bat dates from about 50 million years ago, only 16 million years after the extinction of the dinosaurs.
Molecular phylogenetic studies suggest that most placental orders diverged about 100 to 85 million years ago and that modern families appeared in the period from the late Eocene through the Miocene. However, no placental fossils have been found from before the end of the Cretaceous. The earliest undisputed fossils of placentals comes from the early Paleocene, after the extinction of the dinosaurs. In particular, scientists have identified an early Paleocene animal named Protungulatum donnae as one of the first placental mammals. The earliest known ancestor of primates is Archicebus achilles from around 55 million years ago. This tiny primate weighed 20–30 grams (0.7–1.1 ounce) and could fit within a human palm.
Anatomy and morphology
Living mammal species can be identified by the presence of sweat glands, including those that are specialized to produce milk to nourish their young. In classifying fossils, however, other features must be used, since soft tissue glands and many other features are not visible in fossils.
Many traits shared by all living mammals appeared among the earliest members of the group:
- Jaw joint - The dentary (the lower jaw bone, which carries the teeth) and the squamosal (a small cranial bone) meet to form the joint. In most gnathostomes, including early therapsids, the joint consists of the articular (a small bone at the back of the lower jaw) and quadrate (a small bone at the back of the upper jaw).
- Middle ear - In crown-group mammals, sound is carried from the eardrum by a chain of three bones, the malleus, the incus and the stapes. Ancestrally, the malleus and the incus are derived from the articular and the quadrate bones that constituted the jaw joint of early therapsids.
- Tooth replacement - Teeth are replaced once or (as in toothed whales and murid rodents) not at all, rather than being replaced continually throughout life.
- Prismatic enamel - The enamel coating on the surface of a tooth consists of prisms, solid, rod-like structures extending from the dentin to the tooth's surface.
- Occipital condyles - Two knobs at the base of the skull fit into the topmost neck vertebra; most other tetrapods, in contrast, have only one such knob.
The majority of mammals have seven cervical vertebrae (bones in the neck), including bats, giraffes, whales and humans. The exceptions are the manatee and the two-toed sloth, which have just six, and the three-toed sloth which has nine cervical vertebrae. All mammalian brains possess a neocortex, a brain region unique to mammals. Placental mammals have a corpus callosum, unlike monotremes and marsupials.
The lungs of mammals are spongy and honeycombed. Breathing is mainly achieved with the diaphragm, which divides the thorax from the abdominal cavity, forming a dome convex to the thorax. Contraction of the diaphragm flattens the dome, increasing the volume of the lung cavity. Air enters through the oral and nasal cavities, and travels through the larynx, trachea and bronchi, and expands the alveoli. Relaxing the diaphragm has the opposite effect, decreasing the volume of the lung cavity, causing air to be pushed out of the lungs. During exercise, the abdominal wall contracts, increasing pressure on the diaphragm, which forces air out quicker and more forcefully. The rib cage is able to expand and contract the chest cavity through the action of other respiratory muscles. Consequently, air is sucked into or expelled out of the lungs, always moving down its pressure gradient. This type of lung is known as a bellows lung due to its resemblance to blacksmith bellows.
The integumentary system is made up of three layers: the outermost epidermis, the dermis and the hypodermis. The epidermis is typically 10 to 30 cells thick; its main function is to provide a waterproof layer. Its outermost cells are constantly lost; its bottommost cells are constantly dividing and pushing upward. The middle layer, the dermis, is 15 to 40 times thicker than the epidermis. The dermis is made up of many components, such as bony structures and blood vessels. The hypodermis is made up of adipose tissue. Its job is to store lipids, and to provide cushioning and insulation. The thickness of this layer varies widely from species to species.:97 Although other animals have features such as whiskers, feathers, setae, or cilia that superficially resemble it, no animals other than mammals have hair. It is a definitive characteristic of the class. Though some mammals have very little, careful examination reveals the characteristic, often in obscure parts of their bodies.:61
Herbivores have developed a diverse range of physical structures to facilitate the consumption of plant material. To break up intact plant tissues, mammals have developed teeth structures that reflect their feeding preferences. For instance, frugivores (animals that feed primarily on fruit) and herbivores that feed on soft foliage have low-crowned teeth specialized for grinding foliage and seeds. Grazing animals that tend to eat hard, silica-rich grasses, have high-crowned teeth, which are capable of grinding tough plant tissues and do not wear down as quickly as low-crowned teeth. Most carnivorous mammals have carnassialiforme teeth (of varying length depending on diet), long canines and similar tooth replacement patterns.
The stomach of Artiodactyls is divided into four sections: the rumen, the reticulum, the omasum and the abomasum (only ruminants have a rumen). After the plant material is consumed, it is mixed with saliva in the rumen and reticulum and separates into solid and liquid material. The solids lump together to form a bolus (or cud), and is regurgitated. When the bolus enters the mouth, the fluid is squeezed out with the tongue and swallowed again. Ingested food passes to the rumen and reticulum where cellulytic microbes (bacteria, protozoa and fungi) produce cellulase, which is needed to break down the cellulose in plants. Perissodactyls, in contrast to the ruminants, store digested food that has left the stomach in an enlarged cecum, where it is fermented by bacteria. Carnivora have a simple stomach adapted to digest primarily meat, as compared to the elaborate digestive systems of herbivorous animals, which are necessary to break down tough, complex plant fibers. The caecum is either absent or short and simple, and the large intestine is not sacculated or much wider than the small intestine.
The mammalian heart has four chambers, two upper atria, the receiving chambers, and two lower ventricles, the discharging chambers. The heart has four valves, which separate its chambers and ensures blood flows in the correct direction through the heart (preventing backflow). After gas exchange in the pulmonary capillaries (blood vessels in the lungs), oxygen-rich blood returns to the left atrium via one of the four pulmonary veins. Blood flows nearly continuously back into the atrium, which acts as the receiving chamber, and from here through an opening into the left ventricle. Most blood flows passively into the heart while both the atria and ventricles are relaxed, but toward the end of the ventricular relaxation period, the left atrium will contract, pumping blood into the ventricle. The heart also requires nutrients and oxygen found in blood like other muscles, and is supplied via coronary arteries.
Mammalian hair, also known as pelage, can vary in color between populations, organisms within a population, and even on the individual organism. Light-dark color variation is common in the mammalian taxa. Sometimes, this color variation is determined by age variation, however, in other cases, it is determined by other factors. Selective pressures, such as ecological interactions with other populations or environmental conditions, often lead to the variation in mammalian coloration. These selective pressures favor certain colors in order to increase survival. Camouflage is thought to be a major selection pressure shaping coloration in mammals, although there is also evidence that sexual selection, communication and physiological processes may influence its evolution as well. Camouflage is the most predominant mechanism for color variation, as it aids in the concealment of the organisms from predators or from their prey. Sloths sometimes appear to have green fur and blend into their green jungle environment, but this color is caused by algal growths.
Coat color can also be for intraspecies communication such as warning members of their species about predators, indicating health for reproductive purposes, communicating between mother and young and intimidating predators. Studies have shown that in some cases, differences in female and male coat color could indicate information nutrition and hormone levels, which are important in the mate selection process. For example, some primates and marsupials have shades of violet, green, or blue skin on parts of their bodies, which indicates some distinct advantage in their largely arboreal habitat due to convergent evolution.
Another mechanism for coat color variation is physiological response purposes, such as temperature regulation in tropical or arctic environments. Although much has been observed about color variation, much of the genetic that link coat color to genes is still unknown. The genetic sites where pigmentation genes are found are known to affect phenotype by altering the spatial distribution of pigmentation of the hairs, and altering the density and distribution of the hairs. Although the genetic sites are known, it is largely unknown how these genes are expressed.
Most mammals are viviparous, giving birth to live young. However, the five species of monotreme, the platypus and the four species of echidna, lay eggs. The monotremes have a sex determination system different from that of most other mammals. In particular, the sex chromosomes of a platypus are more like those of a chicken than those of a therian mammal.
The mammary glands of mammals are specialized to produce milk, the primary source of nutrition for newborns. The monotremes branched early from other mammals and do not have the nipples seen in most mammals, but they do have mammary glands. The young lick the milk from a mammary patch on the mother's belly.
Viviparous mammals are in the subclass Theria; those living today are in the marsupial and placental infraclasses. Marsupials have a short gestation period, typically shorter than its estrous cycle and gives birth to an undeveloped newborn that then undergoes further development; in many species, this takes place within a pouch-like sac, the marsupium, located in the front of the mother's abdomen. This is the plesiomorphic condition among viviparous mammals; the presence of epipubic bones in all non-placental mammals prevents the expansion of the torso needed for full pregnancy. Even non-placental eutherians probably reproduced this way. The placentals are unusual among mammals in giving birth to complete and fully developed young, usually after long gestation periods.
Nearly all mammals are endothermic ("warm-blooded"). Most mammals also have hair to help keep them warm. Like birds, mammals can forage or hunt in weather and climates too cold for nonavian reptiles and large insects. Endothermy requires plenty of food energy, so mammals eat more food per unit of body weight than most reptiles. Small insectivorous mammals eat prodigious amounts for their size. A rare exception, the naked mole-rat produces little metabolic heat, so it is considered an operational poikilotherm. Birds are also endothermic, so endothermy is not unique to mammals.
To maintain a high constant body temperature is energy expensive – mammals therefore need a nutritious and plentiful diet. While the earliest mammals were probably predators, different species have since adapted to meet their dietary requirements in a variety of ways. Some eat other animals – this is a carnivorous diet (and includes insectivorous diets). Other mammals, called herbivores, eat plants. An herbivorous diet includes subtypes such as granivory (seed eating), folivory (leaf eating), frugivory (fruit eating), nectivory (nectar eating), gummivory (gum eating) and mycophagy (fungus eating). Some mammals may be coprophagous, and consume feces, usually to consume more nutrients.:131–137 An omnivore eats both prey and plants. Carnivorous mammals have a simple digestive tract because the proteins, lipids and minerals found in meat require little in the way of specialized digestion. Plants on the other hand contain complex carbohydrates, such as cellulose. The digestive tract of an herbivore is therefore host to bacteria that ferment these substances, and make them available for digestion. The bacteria are either housed in the multichambered stomach or in a large cecum.
The size of an animal is also a factor in determining diet type (Allen's rule). Since small mammals have a high ratio of heat-losing surface area to heat-generating volume, they tend to have high energy requirements and a high metabolic rate. Mammals that weigh less than about 18 oz (500 g) are mostly insectivorous because they cannot tolerate the slow, complex digestive process of an herbivore. Larger animals, on the other hand, generate more heat and less of this heat is lost. They can therefore tolerate either a slower collection process (those that prey on larger vertebrates) or a slower digestive process (herbivores). Furthermore, mammals that weigh more than 18 oz (500 g) usually cannot collect enough insects during their waking hours to sustain themselves. The only large insectivorous mammals are those that feed on huge colonies of insects (ants or termites).
In intelligent mammals, such as primates, the cerebrum is larger relative to the rest of the brain. Intelligence itself is not easy to define, but indications of intelligence include the ability to learn, matched with behavioral flexibility. Rats, for example, are considered to be highly intelligent, as they can learn and perform new tasks, an ability that may be important when they first colonize a fresh habitat. In some mammals, food gathering appears to be related to intelligence: a deer feeding on plants has a brain smaller than a cat, which must think to outwit its prey.
Tool use by animals may indicate different levels of learning and cognition. The sea otter uses rocks as essential and regular parts of its foraging behaviour (smashing abalone off of rocks or breaking open shells), with some populations spending 21% of their time making tools. Other tool use, such as chimpanzees using twigs to "fish" for termites, may be developed by watching others use tools and may even be a true example of animal teaching. Tools may even be used in solving puzzles in which the animal appears to experience a "Eureka moment". Other mammals that do not use tools, such as dogs, can also experience a Eureka moment.
Brain size was previously considered a major indicator of the intelligence of an animal. Since most of the brain is used for maintaining bodily functions, greater ratios of brain to body mass may increase the amount of brain mass available for more complex cognitive tasks. Allometric analysis indicates that mammalian brain size scales at approximately the ⅔ or ¾ exponent of the body mass. Comparison of a particular animal's brain size with the expected brain size based on such allometric analysis provides an encephalisation quotient that can be used as another indication of animal intelligence. Sperm whales have the largest brain mass of any animal on earth, averaging 8,000 cubic centimetres (490 in3) and 7.8 kilograms (17 lb) in mature males.
Self-awareness appears to be a sign of abstract thinking. Self-awareness, although not well-defined, is believed to be a precursor to more advanced processes such as metacognitive reasoning. The traditional method for measuring this is the mirror test, which determines if an animals possesses the ability of self-recognition. Mammals that have 'passed' the mirror test are:
- Asian elephants, however not all subjects have passed. Three female elephants were tested, but only one passed, and two other elephants tested in another study also failed to pass.
- Chimpanzees, but mirror tests with a juvenile (11 months old) male chimpanzee failed to reveal self-recognition.
- Bonobos 
- Bornean orangutan 
- Sumatran orangutan 
- Humans, which show signs of self-recognition at 18 months (mirror stage)
- Bottlenose dolphins, since they don't have arms and can't touch the marked areas, decreased latency to approach the mirror, repetitious head circling and close viewing of the marked areas were considered signs of self-recognition 
- Killer whales 
- False killer whales 
Eusociality is the highest level of social organization. These societies have an overlap of adult generations, the division of reproductive labor and cooperative caring of young. Usually insects, such as bees, ants and termites, have eusocial behavior, but it is demonstrated in two rodent species: the naked mole-rat and the Damaraland mole-rat.
Presociality is when animals exhibit more than just sexual interactions with members of the same species, but fall short of qualifying as eusocial. That is, presocial animals can display communal living, cooperative care of young, or primitive division of reproductive labor, but they do not display all of the three essential traits of eusocial animals. Humans and some species of Callitrichidae are unique among primates in their degree of cooperative care of young. Harry Harlow set up an experiment with rhesus monkeys, presocial primates, in 1958; the results from this study showed that social encounters are necessary in order for the young monkeys to develop both mentally and sexually.
A fission-fusion society are societies that change frequently in their size and composition, making up a permanent social group called the "parent group". Permanent social networks consist of all individual members of a community and often varies to track changes in their environment. In a fission–fusion society, the main parent group can fracture (fission) into smaller stable subgroups or individuals to adapt to environmental or social circumstances. For example, a number of males may break off from the main group in order to hunt or forage for food during the day, but at night they may return to join (fusion) the primary group to share food and partake in other activities. Many mammals exhibit this, such as primates (for example orangutans and spider monkeys), elephants, hyenas, lions, and dolphins.
Solitary animals defend a territory and avoid social interactions with the members of its species, except during breeding season. This is to avoid resource competition, as two individuals of the same species would occupy the same niche, and prevent depletion of food. A solitary animal, while foraging, can also be less conspicuous to predators or prey.
In a hierarchy, individuals are either dominant or submissive. A despotic hierarchy is where one individual is dominant while the others are submissive, as in wolves and lemurs, and a pecking order which is a linear ranking of individuals where there is a top individual and a bottom individual. Pecking orders may also be ranked by sex, where the lowest individual of a sex has a higher ranking than the top individual of the other sex, as in hyenas. Dominant individuals, or alphas, have a high chance of reproductive success, especially in harems where one or a few males (resident males) have exclusive breeding rights to females in a group. Non-resident males can also be accepted in harems, but some species may be more strict.
When two animals mate, they both share an interest in the success of the offspring, though often to different extremes. Unless the male and female are perfectly monogamous, meaning that they mate for life and take no other partners, even after the original mate’s death, as with wolves, Eurasian beavers, and otters. The amount of parental care will vary. There are three types of polygamy: either one or multiple dominant males have with breeding rights (polygyny), multiple males that females mate with (polyandry), or multiple males have exclusive relations with multiple females (polygynandry). It is much more common for polygynous mating to happen, which, excluding leks, are estimated to occur in up to 90% of mammals. Lek mating occurs in harems, wherein one or a few males protect their harem of females from other males who would otherwise mate with the females, as in elephant seals; or males congregate around females and try to attract them with various courtship displays and vocalizations, as in harbor seals.
Most vertebrates—the amphibians, the reptiles and some mammals such as humans and bears—are plantigrade, walking on the whole of the underside of the foot. Many mammals, such as cats and dogs are digitigrade, walking on their toes, the greater stride length allowing more speed. Digitigrade mammals are also often adept at quiet movement. Some animals such as horses are unguligrade, walking on the tips of their toes. This even further increases their stride length and thus their speed. A few mammals, namely the great apes, are also known to walk on their knuckles, at least for their front legs. Giant anteaters and platypuses are also knuckle-walkers.
Animals will use different gaits for different speeds, terrain and situations. For example, horses show four natural gaits, the slowest horse gait is the walk, then there are three faster gaits which, from slowest to fastest, are the trot, the canter and the gallop. Animals may also have unusual gaits that are used occasionally, such as for moving sideways or backwards. For example, the main human gaits are bipedal walking and running, but they employ many other gaits occasionally, including a four-legged crawl in tight spaces. Mammals show a vast range of gaits, the order that they place and lift their appendages in locomotion. Gaits can be grouped into categories according to their patterns of support sequence. For quadrupeds, there are three main categories: walking gaits, running gaits and leaping gaits. Walking is the most common gait, where some feet are on the ground at any given time, and found in almost all legged animals. Running is considered to occur when at some points in the stride all feet are off the ground in a moment of suspension.
Arboreal animals frequently have elongated limbs that help them cross gaps, reach fruit or other resources, test the firmness of support ahead and, in some cases, to brachiate. Many arboreal species, such as tree porcupines, Silky Anteaters, spider monkeys and possums, use prehensile tails to grasp branches. In the spider monkey, the tip of the tail has either a bare patch or adhesive pad, which provides increased friction. Claws can be used to interact with rough substrates and re-orient the direction of forces the animal applies. This is what allows squirrels to climb tree trunks that are so large to be essentially flat from the perspective of such a small animal. However, claws can interfere with an animal's ability to grasp very small branches, as they may wrap too far around and prick the animal's own paw. Frictional gripping is used by primates, relying upon hairless fingertips. Squeezing the branch between the fingertips generates frictional force that holds the animal's hand to the branch. However, this type of grip depends upon the angle of the frictional force, thus upon the diameter of the branch, with larger branches resulting in reduced gripping ability. To control descent, especially down large diameter branches, some arboreal animals such as squirrels have evolved highly mobile ankle joints that permit rotating the foot into a 'reversed' posture. This allows the claws to hook into the rough surface of the bark, opposing the force of gravity. Small size provides many advantages to arboreal species: such as increasing the relative size of branches to the animal, lower center of mass, increased stability, lower mass (allowing movement on smaller branches) and the ability to move through more cluttered habitat. Size relating to weight affects gliding animals such as the sugar glider. Some species of primate, bat and all species of sloth achieve passive stability by hanging beneath the branch. Both pitching and tipping become irrelevant, as the only method of failure would be losing their grip.
Bats are the only mammals that can truly fly. They fly through the air at a constant speed by moving their wings up and down (usually with some fore-aft movement as well). Because the animal is in motion, there is some airflow relative to its body which, combined with the velocity of the wings, generates a faster airflow moving over the wing. This will generate a lift force vector pointing forwards and upwards, and a drag force vector pointing rearwards and upwards. The upwards components of these counteract gravity, keeping the body in the air, while the forward component provides thrust to counteract both the drag from the wing and from the body as a whole.
The wings of bats are much thinner and consist of more bones than that of birds, allowing bats to maneuver more accurately and fly with more lift and less drag. By folding the wings inwards towards their body on the upstroke, they use 35% less energy during flight than birds. The membranes are delicate, ripping easily; however, the tissue of the bat's membrane is able to regrow, such that small tears can heal quickly. The surface of their wings is equipped with touch-sensitive receptors on small bumps called Merkel cells, also found on human fingertips. These sensitive areas are different in bats, as each bump has a tiny hair in the center, making it even more sensitive and allowing the bat to detect and collect information about the air flowing over its wings, and to fly more efficiently by changing the shape of its wings in response.
Fossorial creatures live in subterranean environments. Many fossorial mammals were classified under the, now obsolete, order Insectivora, such as shrews, hedgehogs and moles. Fossorial mammals have a fusiform body, thickest at the shoulders and tapering off at the tail and nose. Unable to see in the dark burrows, most have degenerated eyes, but degeneration varies between species; pocket gophers, for example, are only semi-fossorial and have very small yet functional eyes, in the fully fossorial marsupial mole the eyes are degenerated and useless, talpa moles have vestigial eyes and the cape golden mole has a layer of skin covering the eyes. External ears flaps are also very small or absent. Truly-fossorial mammals have short, stout legs as strength is more important than speed to a burrowing mammal, but semi-fossorial mammals have cursorial legs. The front paws are broad and have strong claws to help in loosening dirt while excavating burrows, and the back paws have webbing, as well as claws, which aids in throwing loosened dirt backwards. Most have large incisors to prevent dirt from flying into their mouth.
Fully aquatic mammals, the cetaceans and sirenians, have lost their legs and have a tail fin to propel themselves through the water. Flipper movement is continuous. Whales swim by moving their tail fin and lower body up and down, propelling themselves through vertical movement, while their flippers are mainly used for steering. Their skeletal anatomy allows them to be fast swimmers. Most species have a dorsal fin to prevent themselves from turning upside-down in the water. The flukes of sirenians are raised up and down in long strokes to move the animal forward, and can be twisted to turn. The forelimbs are paddle-like flippers which aid in turning and slowing.
Semi-aquatic mammals, like pinnipeds, have two pairs of flippers on the front and back, the fore-flippers and hind-flippers. The elbows and ankles are enclosed within the body. Pinnipeds have several adaptions for reducing drag. In addition to their streamlined bodies, they have smooth networks of muscle bundles in their skin that may increase laminar flow and make it easier for them to slip through water. They also lack arrector pili, so their fur can be streamlined as they swim. They rely on their fore-flippers for locomotion in a wing-like manner similar to penguins and sea turtles. Fore-flipper movement is not continuous, and the animal glides between each stroke. Compared to terrestrial carnivorans, the fore-limbs are reduced in length, which gives the locomotor muscles at the shoulder and elbow joints greater mechanical advantage; the hind-flippers serve as stabilizers. Other semi-aquatic mammals include beavers, hippopotamuses, otters and platypuses. Hippos are very large semi-aquatic mammals, and their barrel-shaped bodies have graviportal skeletal structures, adapted to carrying their enormous weight, and their specific gravity allows them to sink and move along the bottom of a river.
Hybrids are offspring resulting from the breeding of two genetically distinct individuals, which usually will result in a high degree of heterozygosity, though hybrid and heterozygous are not synonymous. The deliberate or accidental hybridizing of two or more species of closely related animals through captive breeding is a human activity which has been in existence for millennia and has grown for economic purposes (Domestication syndrome). Hybrids between different subspecies within a species (such as between the Bengal tiger and Siberian tiger) are known as intra-specific hybrids. Hybrids between different species within the same genus (such as between lions and tigers) are known as interspecific hybrids or crosses. Hybrids between different genera (such as between sheep and goats) are known as intergeneric hybrids. Natural hybrids will occur in hybrid zones, where two populations of species within the same genera or species living in the same or adjacent areas will interbreed with each other. Some hybrids have been recognized as species, such as the red wolf (though this is controversial).
Artificial selection, the deliberate selective breeding of domestic animals, is being used to breed back recently extinct animals in an attempt to achieve an animal breed with a phenotype that resembles that extinct wildtype ancestor. A breeding-back (intraspecific) hybrid may be very similar to the extinct wild type in phenotype, ecological niche and to some extent genetics, but the initial gene pool of that wild type is lost forever with its extinction. As a result, some breeds, like Heck cattle, are vague look-alikes of the extinct wildtype aurochs.
- List of recently extinct mammals – during recorded history
- List of prehistoric mammals
- List of monotremes and marsupials
- List of placental mammals
- Prehistoric mammals
- List of mammal genera – living mammals
- List of mammalogists
- Lists of mammals by population size
- Lists of mammals by region
- List of threatened mammals of the United States
- Mammals described in the 2000s
- Vaughan, Terry A.; Ryan, James M.; Czaplewski, Nicholas J. (2015), "Chapter 4: Classification of Mammals", Mammalogy (Sixth ed.), ISBN 9781284032093
- Szalay, Frederick S. (1999). "Classification of Mammals above the Species Level: Review". Journal of Vertebrate Paleontology 19 (1): 191–195. doi:10.1080/02724634.1999.10011133.
- Rowe, T. (1988). "Definition, diagnosis, and origin of Mammalia" (PDF). Journal of Vertebrate Paleontology 8 (3): 241–264. doi:10.1080/02724634.1988.10011708.
- Lyell, Charles (1871). The Student's Elements of Geology. London: John Murray. p. 347. Retrieved August 12, 2013.
- Cifelli, Richard L.; Davis, Brian M. (2003). "Marsupial origins". Science 302 (5652): 1899–1900. doi:10.1126/science.1092272. PMID 14671280.
- Kemp, T. S. (2005). The Origin and Evolution of Mammals (PDF). United Kingdom: Oxford University Press. p. 3. ISBN 0-19-850760-7. OCLC 232311794.
- Datta, P. M. (2005). "Earliest mammal with transversely expanded upper molar from the Late Triassic (Carnian) Tiki Formation, South Rewa Gondwana Basin, India". Journal of Vertebrate Paleontology 25 (1): 200–207. doi:10.1671/0272-4634(2005)025[0200:EMWTEU]2.0.CO;2.
- Luo, Zhe-Xi; Martin, Thomas (2007). "Analysis of Molar Structure and Phylogeny of Docodont Genera" (PDF). Bulletin of Carnegie Museum of Natural History 39: 27–47. doi:10.2992/0145-9058(2007)39[27:AOMSAP]2.0.CO;2. Retrieved April 8, 2013.
- McKenna, Malcolm C.; Bell, Susan Groag (1997). Classification of Mammals above the Species Level. New York: Columbia University Press. ISBN 0-231-11013-8. OCLC 37345734.
- Schiewe, Jessie (2010-07-28). "Australia's marsupials originated in what is now South America, study says". LATimes.Com. Los Angeles Times. Archived from the original on 1 August 2010. Retrieved 2010-08-01. External link in |work= (help)
- Nilsson, M. A.; Churakov, G.; , Sommer, M.; Van Tran, N.; Zemann, A.; Brosius, J.; Schmitz, J. (2010-07-27). "Tracking Marsupial Evolution Using Archaic Genomic Retroposon Insertions". PLoS Biology (Public Library of Science) 8 (7): e1000436. doi:10.1371/journal.pbio.1000436. PMC 2910653. PMID 20668664.
- Kriegs, Jan Ole; Churakov, Gennady; Kiefmann, Martin; Jordan, Ursula; Brosius, Jürgen; Schmitz, Jürgen (2006). "Retroposed Elements as Archives for the Evolutionary History of Placental Mammals". PLoS Biology 4 (4): e91. doi:10.1371/journal.pbio.0040091. PMC 1395351. PMID 16515367.
- Nishihara, H.; Maruyama, S.; Okada, N. (2009). "Retroposon analysis and recent geological data suggest near-simultaneous divergence of the three superorders of mammals". Proceedings of the National Academy of Sciences 106 (13): 5235–5240. doi:10.1073/pnas.0809297106.
- Springer, Mark S.; Murphy, William J.; Eizirik, Eduardo; O'Brien, Stephen J. (2003). "Placental mammal diversification and the Cretaceous–Tertiary boundary". Proceedings of the National Academy of Sciences 100 (3): 1056–1061. doi:10.1073/pnas.0334222100. PMC 298725. PMID 12552136.
- Tarver, J.E. et al. (2016) The Interrelationships of Placental Mammals and the Limits of Phylogenetic Inference. Genome Biol Evol, (2016) 8 (2): 330-344. doi: 10.1093/gbe/evv261
- Wilson, D.E.; Reeder, D.M., eds. (2005). "Preface and introductory material". Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. p. xxvi. ISBN 978-0-8018-8221-0. OCLC 62265494.
- "Initiatives". The IUCN Red List of Threatened Species. IUCN. April 2010.
- Jin Meng, Yuanqing Wang & Chuankui Li (2011). "Transitional mammalian middle ear from a new Cretaceous Jehol eutriconodont". Nature 472 (7342): 181–185. Bibcode:2011Natur.472..181M. doi:10.1038/nature09921. PMID 21490668.
- Haaramo, Mikko. "Mammaliaformes– mammals and near-mammals". Mikko's Phylogeny Archive.
- Ahlberg, P. E. & Milner, A. R. (April 1994). "The Origin and Early Diversification of Tetrapods". Nature 368 (6471): 507–514. Bibcode:1994Natur.368..507A. doi:10.1038/368507a0. Retrieved 2008-09-06.
- "Amniota – Palaeos". Archived from the original on 2010-12-20.
- "Synapsida overview – Palaeos". Archived from the original on 2010-12-20.
- Kemp, T. S. (2006). "The origin and early radiation of the therapsid mammal-like reptiles: a palaeobiological hypothesis" (PDF). Journal of Evolutionary Biology 19 (4): 1231–47. doi:10.1111/j.1420-9101.2005.01076.x. PMID 16780524.
- Bennett, A. F. and Ruben, J. A. (1986) "The metabolic and thermoregulatory status of therapsids"; pp. 207–218 in N. Hotton III, P. D. MacLean, J. J. Roth and E. C. Roth (eds), "The ecology and biology of mammal-like reptiles", Smithsonian Institution Press, Washington.
- Kermack, D.M.; Kermack, K.A. (1984). The evolution of mammalian characters. Washington D.C.: Croom Helm. ISBN 0-7099-1534-9. OCLC 10710687.
- Tanner LH, Lucas SG & Chapman MG (2004). "Assessing the record and causes of Late Triassic extinctions" (PDF). Earth-Science Reviews 65 (1–2): 103–139. Bibcode:2004ESRv...65..103T. doi:10.1016/S0012-8252(03)00082-5. Archived from the original on October 25, 2007.
- Stephen L. Brusatte. "Superiority, Competition, and Opportunism in the Evolutionary Radiation of Dinosaurs".
- Gauthier, J.A. (1986). "Saurischian monophyly and the origin of birds". In Padian, K. (ed.). The Origin of Birds and the Evolution of Flight. Memoirs of the California Academy of Sciences 8. San Francisco: California Academy of Sciences. pp. 1–55.
- Sereno, P.C. (1991). "Basal archosaurs: phylogenetic relationships and functional implications". Memoirs of the Society of Vertebrate Paleontology 2: 1–53. doi:10.2307/3889336. JSTOR 3889336.
- MacLeod, N, Rawson, PF, Forey, PL, Banner, FT, Boudagher-Fadel, MK, Bown, PR, Burnett, JA, Chambers, P, Culver, S, Evans, SE, Jeffery, C, Kaminski, MA, Lord, AR, Milner, AC, Milner, AR, Morris, N, Owen, E, Rosen, BR, Smith, AB, Taylor, PD, Urquhart, E & Young, JR (1997). "The Cretaceous–Tertiary biotic transition". Journal of the Geological Society 154 (2): 265–292. doi:10.1144/gsjgs.154.2.0265.
- Hunt, David M.; Hankins, Mark W.; Collin, Shaun P.; Marshall, N. J. Evolution of Visual and Non-visual Pigments. London: Springer. p. 73. ISBN 978-1-4614-4354-4. OCLC 892735337.
- Bakalar, Nicholas (2006). "Jurassic "Beaver" Found; Rewrites History of Mammals". National Geographic News. Retrieved 28 May 2016.
- Hall, M. I.; Kamilar, J. M.; Kirk, E. C. (24 October 2012). "Eye shape and the nocturnal bottleneck of mammals". Proceedings of the Royal Society B: Biological Sciences 279 (1749): 4962–4968. doi:10.1098/rspb.2012.2258. PMID 23097513.
- Luo, Zhe-Xi (2007). "Transformation and diversification in early mammal evolution". Nature 450 (7172): 1011–19. Bibcode:2007Natur.450.1011L. doi:10.1038/nature06277. PMID 18075580.
- Pickrell, John (2003). "Oldest Marsupial Fossil Found in China". National Geographic News. Retrieved 28 May 2016.
- Luo, Zhe-Xi; Yuan, Chong-Xi; Meng, Qing-Jin; Ji, Qiang (2011). "A Jurassic eutherian mammal and divergence of marsupials and placentals". Nature 476 (7361): 442–445. Bibcode:2011Natur.476..442L. doi:10.1038/nature10291. PMID 21866158.
- Ji, Qiang; Luo, Zhe-Xi; Yuan, Chong-Xi; Wible, John R.; Zhang, Jian-Ping; Georgi, Justin A. (2002). "The earliest known eutherian mammal". Nature 416: 816–822. doi:10.1038/416816a.
- M. J. Novacek; G. W. Rougier; J. R. Wible; M. C. McKenna; D. Dashzeveg & I. Horovitz (1997). "Epipubic bones in eutherian mammals from the Late Cretaceous of Mongolia". Nature 389 (6650): 483–486. Bibcode:1997Natur.389..483N. doi:10.1038/39020. PMID 9333234.
- Rowe, Timothy; Rich, Thomas H.; Vickers-Rich, Patricia; Springer, Mark; Woodburne, Michael O. (2007). "The oldest platypus and its bearing on divergence timing of the platypus and echidna clades". Proceedings of the National Academy of Sciences 105 (4): 1238–1242. doi:10.1073/pnas.0706385105.
- Grant, Tom (1995). "Reproduction". The Platypus: A Unique Mammal. Sydney: University of New South Wales. p. 55. ISBN 978-0-86840-143-0. OCLC 33842474.
- Goldman, Armond S. (2012). "Evolution of Immune Functions of the Mammary Gland and Protection of the Infant". Breastfeeding Medicine 7 (3): 132–142. doi:10.1089/bfm.2012.0025.
- Rose, Kenneth D. (2006). The Beginning of the Age of Mammals. Baltimore: Johns Hopkins University Press. pp. 82–83. ISBN 978-0-8018-8472-6. OCLC 646769601.
- Brink, A.S. (1955). "A study on the skeleton of Diademodon". Palaeontologia Africana 3: 3–39.
- Kemp, T.S. (1982). Mammal-like reptiles and the origin of mammals. London: Academic Press. p. 363. ISBN 978-0-12-404120-2. OCLC 8613180.
- Estes, R. (1961). "Cranial anatomy of the cynodont reptile Thrinaxodon liorhinus". Bulletin of the Museum of Comparative Zoology (1253): 165–180.
- "Thrinaxodon: The Emerging Mammal". National Geographic Daily News. February 11, 2009. Retrieved August 26, 2012.
- Bajdek, Piotr; Qvarnström, Martin; Owocki, Krzysztof; Sulej, Tomasz; Sennikov, Andrey G.; Golubev, Valeriy K.; Niedźwiedzki, Grzegorz (2015). "Microbiota and food residues including possible evidence of pre-mammalian hair in Upper Permian coprolites from Russia". doi:10.1111/let.12156.
- Botha-Brink, Jennifer; Angielczyk, Kenneth D. (2010). "Do extraordinarily high growth rates in Permo-Triassic dicynodonts (Therapsida, Anomodontia) explain their success before and after the end-Permian extinction?" 160 (2): 341–365. doi:10.1111/j.1096-3642.2009.00601.x.
- Paul, G.S. (1988). Predatory Dinosaurs of the World. New York: Simon and Schuster. p. 464. ISBN 978-0-671-61946-6. OCLC 18350868.
- J.M. Watson & J.A.M. Graves (1988). "Monotreme Cell-Cycles and the Evolution of Homeothermy". Australian Journal of Zoology (CSIRO) 36 (5): 573–584. doi:10.1071/ZO9880573.
- McNab, Brian K. (1980). "Energetics and the limits to the temperate distribution in armadillos". Journal of Mammalogy (American Society of Mammalogists) 61 (4): 606–627. doi:10.2307/1380307. JSTOR 1380307.
- Kielan−Jaworowska, Z.; Hurum, J.H.. (2006). "Limb posture in early mammals: Sprawling or parasagittal" (PDF). Acta Palaeontologica Polonica 51 (3): 10237–10239.
- Lillegraven, Jason A.; Kielan-Jaworowska, Zofia; Clemens, William A. (1979). Mesozoic Mammals: The First Two-Thirds of Mammalian History. University of California Press. p. 321. ISBN 978-0-520-03951-3. OCLC 5910695.
- Oftedal, O.T. (2002). "The mammary gland and its origin during synapsid evolution". Journal of Mammary Gland Biology and Neoplasia 7 (3): 225–252. doi:10.1023/A:1022896515287. PMID 12751889.
- Oftedal, O.T. (2002). "The origin of lactation as a water source for parchment-shelled eggs". Journal of Mammary Gland Biology and Neoplasia 7 (3): 253–266. doi:10.1023/A:1022848632125. PMID 12751890.
- Sahney, S., Benton, M.J. and Ferry, P.A. (2010). "Links between global taxonomic diversity, ecological diversity and the expansion of vertebrates on land" (PDF). Biology Letters 6 (4): 544–547. doi:10.1098/rsbl.2009.1024. PMC 2936204. PMID 20106856.
- Simmons, Nancy B.; Seymour, Kevin L.; Habersetzer, Jörg; Gunnell, Gregg F. (2007). "Primitive Early Eocene bat from Wyoming and the evolution of flight and echolocation". Nature 451: 818–821. doi:10.1038/nature06549.
- Bininda-Emonds, O.R.P.; Cardillo, M.; Jones, K.E.; Beck, Robin M. D.; Grenyer, Richard; Price, Samantha A.; Vos, Rutger A.; et al. (2007). "The delayed rise of present-day mammals" (PDF). Nature 446 (7135): 507–511. Bibcode:2007Natur.446..507B. doi:10.1038/nature05634. PMID 17392779.
- Wible, J. R.; Rogier, G. W.; Novacek, M. J.; Asher, R. J. (2007). "Cretaceous eutherians and Laurasian origin for placental mammals near the K/T boundary". Nature 447 (7147): 1003–06. Bibcode:2007Natur.447.1003W. doi:10.1038/nature05854. PMID 17581585.
- O'Leary, Maureen A.; Bloch, Jonathan I.; Flynn, John J.; Gaudin, Timothy J.; Giallombardo, Andres; Giannini, Norberto P.; Goldberg, Suzann L.; Kraatz, Brian P.; Luo, Zhe-Xi; Meng, Jin; Novacek, Michael J.; Perini, Fernando A.; Randall, Zachary S.; Rougier, Guillermo; Sargis, Eric J.; Silcox, Mary T.; Simmons, Nancy b.; Spaulding, Micelle; Velazco, Paul M.; Weksler, Marcelo; Wible, John r.; Cirranello, Andrea L.; Cirranello, Andrea L. (8 February 2013). "The Placental Mammal Ancestor and the Post–K-Pg Radiation of Placentals". Science 339 (6120): 662–667. Bibcode:2013Sci...339..662O. doi:10.1126/science.1229237. PMID 23393258. Retrieved 9 February 2013.
- Ni, Xijun; Gebo, Daniel L.; Dagosto, Marian; Meng, Jin; Tafforeau, Paul; Flynn, John J. Last7=Beard; Beard, K. Christopher (6 June 2013). "The oldest known primate skeleton and early haplorhine evolution". Nature 498 (7452): 60–64. Bibcode:2013Natur.498...60N. doi:10.1038/nature12200. PMID 23739424.
- Romer, Sherwood A.; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia: Holt-Saunders International. pp. 129–145. ISBN 978-0-03-910284-5. OCLC 60007175.
- Purves, William K.; Sadava, David E.; Orians, Gordon H.; Helle, H. C. (2001). Life: The Science of Biology (6 ed.). New York: Sinauer Associates, Inc. p. 593. ISBN 978-0-7167-3873-2. OCLC 874883911.
- Anthwal, Neal; Joshi, Leena; Tucker, Abigail S. (2012). "Evolution of the mammalian middle ear and jaw: adaptations and novel structures". Journal of Anatomy 221 (1): 147–160. doi:10.1111/j.1469-7580.2012.01526.x. PMC 3552421.
- van Nievelt, Alexander F. H.; Smith, Kathleen K. (2005). "To replace or not to replace: the significance of reduced functional tooth replacement in marsupial and placental mammals". Paleobiology 31 (2): 324–346. doi:10.1666/0094-8373(2005)031[0324:trontr]2.0.co;2.
- Mao, Fangyuan; Wang, Yuanqing; Meng, Jin (2015). "A Systematic Study on Tooth Enamel Microstructures of Lambdopsalis bulla (Multituberculate, Mammalia) - Implications for Multituberculate Biology and Phylogeny". PLoS One 10 (5). doi:10.1371/journal.pone.0128243. PMC 4447277.
- Osborn, Henry F. (1900). "Origin of the Mammalia, III. Occipital Condyles of Reptilian Tripartite Type". The American Naturalist 34 (408): 943–947. doi:10.1086/277821.
- Crompton, A. W.; Jenkins, Jr., F. A. (1973). "Mammals from Reptiles: A Review of Mammalian Origins". Annual Review of Earth and Planetary Sciences 1: 131–155. doi:10.1146/annurev.ea.01.050173.001023.
- Power, Michael L.; Schulkin, Jay (2013). The Evolution Of The Human Placenta. Baltimore: Johns Hopkins University Press. pp. 1890–1891. ISBN 978-1-4214-0643-5. OCLC 940749490.
- Dierauf, Leslie A.; Gulland, Frances M. D. (2001). CRC Handbook of Marine Mammal Medicine: Health, Disease, and Rehabilitation (2 ed.). Boca Raton: CRC Press. p. 154. ISBN 978-1-4200-4163-7. OCLC 166505919.
- Lui, J. H.; Hansen, D. V.; Kriegstein, A. R. (2011). "Development and Evolution of the Human Neocortex". Cell 146 (1): 18–36. doi:10.1016/j.cell.2011.06.030. PMC 3610574. PMID 21729779.
- Keeler, Clyde E. (1933). "Absence of the Corpus callosum as a Mendelizing Character in the House Mouse". Proceedings of the National Academy of Sciences of the United States of America 19 (6): 609–11. Bibcode:1933PNAS...19..609K. doi:10.1073/pnas.19.6.609. JSTOR 86284. PMC 1086100. PMID 16587795.
- Levitzky, Michael G. (2013). "Mechanics of Breathing". Pulmonary physiology (8 ed.). New York: McGraw-Hill Medical. ISBN 978-0071793131. OCLC 940633137.
- Umesh, Kumar B. (2011). "Pulmonary Anatomy and Physiology". Handbook of Mechanical Ventilation (1 ed.). New Delhi: Jaypee Brothers Medical Publishing. p. 12. ISBN 978-93-80704-74-6. OCLC 945076700.
- Feldhamer, George A.; Drickamer, Lee C.; Vessey, Stephen H.; Merritt, Joseph H.; Krajewski, Carey (2007). Mammalogy: Adaptation, Diversity, Ecology (3 ed.). Baltimore: Johns Hopkins University Press. ISBN 978-0-8018-8695-9. OCLC 124031907.
- Romer, A. S. (1959). The vertebrate story (4 ed.). Chicago: University of Chicago Press. ISBN 978-0-226-72490-4.
- de Muizon, Christian; Lange-Badré, Brigitte (1997). "Carnivorous dental adaptations in tribosphenic mammals and phylogenetic reconstruction". Lethaia 30 (4): 353–366. doi:10.1111/j.1502-3931.1997.tb00481.x.
- Langer, Peter (1984). "Comparative Anatomy of the Stomach in Mammalian Herbivores". Quarterly Journal of Experimental Physiology 69 (3): 615–625. PMID 6473699.
- Vaughan, Terry A.; Ryan, James M.; Czaplewski, Nicholas J. (2011). "Perissodactyla". Mammalogy (5 ed.). Jones and Bartlett Publishers. p. 322. ISBN 978-0-7637-6299-5. OCLC 437300511.
- Flower, William H.; Lydekker, Richard (1946). An Introduction to the Study of Mammals Living and Extinct. London: Adam and Charles Black. p. 496. ISBN 978-1-110-76857-8.
- Standring, Susan; Borley, Neil R. (2008). Gray's anatomy: the anatomical basis of clinical practice (40 ed.). London: Churchill Livingstone. pp. 960–962. ISBN 978-0-8089-2371-8. OCLC 213447727.
- Betts, J. Gordon; Desaix, Peter; Johnson, Eddie; Johnson, Jody E.; Korol, Oksana; Kruse, Dean; Poe, Brandon; Wise, James A.; Womble, Mark; Young, Kelly A. (2013). Anatomy & physiology. Houston: Rice University Press. pp. 787–846. ISBN 978-1-938168-13-0. OCLC 898069394.
- Bradley et. al, Brenda (2012). "Coat Color Variation and Pigmentation Gene Expression in Rhesus Macaques (Macaca Mulatta)" (PDF). Journal of Mammalian Evolution 20: 263–70. doi:10.1007/s10914-012-9212-3.
- Caro, Tim (2005). "The Adaptive Significance of Coloration in Mammals" (PDF). BioScience 55 (2): 125–136. doi:10.1641/0006-3568(2005)055[0125:tasoci]2.0.co;2.
- Suutari, Milla; Majaneva, Markus; Fewer, David P.; Voirin, Bryson; Aiello, Annette; Friedl, Thomas; Chiarello, Adriano G.; Blomster, Jaanika (2010). "Molecular evidence for a diverse green algal community growing in the hair of sloths and a specific association with Trichophilus welckeri (Chlorophyta, Ulvophyceae)". Evolutionary Biology 10 (86). doi:10.1186/1471-2148-10-86.
- Prum, Richard O.; Torres, Rodolfo H. (2004). "Structural colouration of mammalian skin: convergent evolution of coherently scattering dermal collagen arrays" (PDF). Journal of Experimental Biology 207 (12): 2157–72. doi:10.1242/jeb.00989.
- Hoeskra, HE (2006). "genetics, development, and the evolution of adaptive pigmentation in vertebrates" (PDF). Heredity 97: 222–234. doi:10.1038/sj.hdy.6800861. PMID 16823403.
- Wallis M.C., Waters P.D., Delbridge M.L., Kirby P.J., Pask A.J., Grützner F., Rens W., Ferguson-Smith M.A., Graves J.A.M.; Waters; Delbridge; Kirby; Pask; Grützner; Rens; Ferguson-Smith; Graves; et al. (2007). "Sex determination in platypus and echidna: autosomal location of SOX3 confirms the absence of SRY from monotremes". Chromosome Research 15 (8): 949–959. doi:10.1007/s10577-007-1185-3. PMID 18185981.
- Marshall Graves, Jennifer A. (2008). "Weird Animal Genomes and the Evolution of Vertebrate Sex and Sex Chromosomes" (PDF). Annual Review of Genetics 42: 568–586. doi:10.1146/annurev.genet.42.110807.091714. PMID 18983263.
- Oftedal, O. T. (2002). "The mammary gland and its origin during synapsid evolution". Journal of Mammary Gland Biology and Neoplasia 7 (3): 225–252. PMID 12751889.
- Novacek, Michael J.; Rougier, Guillermo W.; Wible, John R.; McKenna, Malcolm C.; Dashzeveg, Demberelyin; Horovitz, Inés (1997). "Epipubic bones in eutherian mammals from the Late Cretaceous of Mongolia". Nature 389: 483–486. doi:10.1038/39020.
- Morgan, Sally (2005). "Mammal Behavior and Lifestyle". Mammals. Chicago: Raintree. p. 6. ISBN 978-1-4109-1050-9. OCLC 53476660.
- Campbell, Neil A.; Reece, Jane B. (2002). Biology (6 ed.). Benjamin Cummings. p. 845. ISBN 978-080536-624-2. OCLC 47521441.
- Buffenstein, Rochelle; Yahav, Shlomo (1991). "Is the naked mole-rat Hererocephalus glaber an endothermic yet poikilothermic mammal?". Journal of Thermal Biology 16 (4): 227–232. doi:10.1016/0306-4565(91)90030-6.
- Schmidt-Nielsen, Knut; Duke, James B. (1997). "Temperature Effects". Animal Physiology: Adaptation and Environment (5 ed.). Cambridge. p. 218. ISBN 978-0-521-57098-5. OCLC 35744403.
- Naugher, K. B. (2004). "Anteaters (Myrmecophagidae)". In Hutchins, M.; Kleiman, D. G; Geist, V.; McDade, M. С. Grzimek's Animal Life Encyclopedia 13 (2 ed.). Gale. pp. 171–179. ISBN 978-0-7876-7750-3. OCLC 471032508.
- Langer, Peter (1984). "Comparative Anatomy of the Stomach in Mammalian Herbivores". Quarterly Journal of Experimental Physiology 69: 615–625. doi:10.1113/expphysiol.1984.sp002848. PMID 6473699.
- Speaksman, J. R. (1996). "Energetics and the evolution of body size in small terrestrial mammals" (PDF). Symposia of the Zoological Society of London (69): 69–81.
- Don E. Wilson; David Burnie, eds. (2001). Animal: The Definitive Visual Guide to the World's Wildlife (1st ed.). DK Publishing. pp. 86–89. ISBN 978-0-7894-7764-4. OCLC 46422124.
- Mann, Janet; Patterson, Eric M. (2013). "Tool Use by Aquatic Animals" (PDF). Philosophical Transactions of the Royal Society B 368 (1630). doi:10.1098/rstb.2012.0424.
- Raffaele, Paul (2011). Among the Great Apes: Adventures on the Trail of Our Closest Relatives. New York: Harper. p. 83. ISBN 978-0061671-84-5. OCLC 674694369.
- Köhler, Wolfgang (1925). The Mentality of Apes. Liveright. ISBN 978-0-87140-108-3. OCLC 2000769.
- McGowan, R. T.; Rehn, T.; Norling, Y.; Keeling, L. J. (2014). "Positive affect and learning: exploring the "Eureka Effect" in dogs". Animal Cognition 17 (13): 577–587. doi:10.1007/s10071-013-0688-x. PMID 24096703.
- Karbowski, Jan (2007). "Global and regional brain metabolic scaling and its functional consequences". BioMed Central Biology 5 (18). doi:10.1186/1741-7007-5-18.
- Marino, Lori (2007). "Cetacean Brains: How Aquatic Are They?". The Anatomical Record 290 (6): 694–700. doi:10.1002/ar.20530.
- Gallup, Jr., G. G. (1970). "Chimpanzees: Self recognition". Science 167 (3914): 86–87. Bibcode:1970Sci...167...86G. doi:10.1126/science.167.3914.86. PMID 4982211.
- Plotnik, J.M., de Waal, F.B.M. and Reiss, D. (2006). "Self-recognition in an Asian elephant" (PDF). Proceedings of the National Academy of Sciences 103 (45): 17053–17057. Bibcode:2006PNAS..10317053P. doi:10.1073/pnas.0608062103.
- S., Robert (1986). "Ontogeny of mirror behavior in two species of great apes". American Journal of Primatology 10 (2): 109–117. doi:10.1002/ajp.1350100202.
- Walraven, V., van Elsacker, L. and Verheyen, R. (1995). "Reactions of a group of pygmy chimpanzees (Pan paniscus) to their mirror images: evidence of self-recognition". Primates 36: 145–150. doi:10.1007/bf02381922.
- Leakey, Richard (1994). "The Origin of the Mind". The Origin Of Humankind. New York: BasicBooks. p. 150. ISBN 978-0-465-05313-1. OCLC 30739453.
- Archer, John (1992). Ethology and Human Development. Rowman & Littlefield. pp. 215–218. ISBN 978-0-389-20996-6. OCLC 25874476.
- Marten, K.; Psarakos, S. (1995). "Evidence of self-awareness in the bottlenose dolphin (Tursiops truncatus)". In Parker, S.T.; Mitchell, R.; Boccia, M. Self-awareness in Animals and Humans: Developmental Perspectives. Cambridge: Cambridge University Press. pp. 361–379. ISBN 978-0-521-44108-7. OCLC 28180680.
- Delfour, F. & Marten, K. (2001). "Mirror image processing in three marine mammal species: Killer whales (Orcinus orca), false killer whales (Pseudorca crassidens) and California sea lions (Zalophus californianus)". Behavioural Processes 53 (3): 181–190. doi:10.1016/s0376-6357(01)00134-6. PMID 11334706.
- Jarvis, J. U. M. (1981). "Eusociality in a mammal: cooperative breeding in naked mole-rat colonies". Science 212 (4494): 571–573. doi:10.1126/science.7209555.
- Jacobs, D.S.; et al. (1991). "The colony structure and dominance hierarchy of the Damaraland mole-rat, Cryptomys damarensis (Rodentia: Bathyergidae) from Namibia". Journal of Zoology 224 (4): 553–576. doi:10.1111/j.1469-7998.1991.tb03785.x.
- Hardy, Sarah B. (2009). Mothers and Others: The Evolutionary Origins of Mutual Understanding. Boston: Belknap Press of Harvard University Press. pp. 92–93.
- Harlow, H.F. and Suomi, S.J. (1971). "Social Recovery by Isolation-Reared Monkeys", Proceedings of the National Academy of Sciences of the United States of America, 68(7): 1534-1538
- van Schaik, Carel P. (1999). "The Socioecology of Fission-Fusion Sociality in Orangutans". Biomedical and Life Sciences 40 (1): 69–86. doi:10.1007/BF02557703.
- Archie, Elizabeth A.; Cynthia J. Moss; Susan C. Alberts (March 2005). "The ties that bind: genetic relatedness predicts the fission and fusion of social groups in wild African elephants". Proceedings of the Royal Society B 273: 513–522. doi:10.1098/rspb.2005.3361.
- Smith, Jennifer E.; Sandra K. Memenis; Kay E. Holekamp (2007). "Rank-related partner choice in the fission–fusion society of the spotted hyena (Crocuta crocuta)" (PDF). Behavioral Ecology and Sociobiology 61 (5): 753–765. doi:10.1007/s00265-006-0305-y.
- Matoba, Tomoyuki; Kutsukake, Nobuyuki; Hasegawa, Toshikazu (2013). Hayward, Matt, ed. "Head Rubbing and Licking Reinforce Social Bonds in a Group of Captive African Lions, Panthera leo". PLoS ONE 8 (9). doi:10.1371/journal.pone.0073044. PMC 3762833.
- Krützen, Michael; Barré, Lynne M.; Connor, Richard C.; Mann, Janet; Sherwin, William B. (2004). "‘O father: where art thou?’— Paternity assessment in an open fission–fusion society of wild bottlenose dolphins (Tursiops sp.) in Shark Bay, Western Australia". Molecular Ecology 13 (7): 1975–1990. doi:10.1111/j.1365-294X.2004.02192.x.
- Martin, Claude (1991). The Rainforests of West Africa: Ecology — Threats — Conservation (1 ed.). Springer Basel AG. doi:10.1007/978-3-0348-7726-8. ISBN 978-3-0348-7726-8.
- le Roux, Aliza; Michael I. Cherry; Lorenz Gygax (5 May 2009). "Vigilance behaviour and fitness consequences: comparing a solitary foraging and an obligate group-foraging mammal". Behavioral Ecology and Sociobiology 63: 1097–1107. doi:10.1007/s00265-009-0762-1.
- Palagi, Elisabetta; Norscia, Ivan (2015). Samonds, Karen E., ed. "The Season for Peace: Reconciliation in a Despotic Species (Lemur catta)". PLoS ONE 10 (11). doi:10.1371/journal.pone.0142150. PMC 4646466.
- East, Marion L.; Hofer, Heribert (2000). "Male spotted hyenas (Crocuta crocuta) queue for status in social groups dominated by females". Behavioral Ecology 12 (15): 558–568. doi:10.1093/beheco/12.5.558.
- Samuels, A; Silk, J. B.; Rodman, P. (1984). "Changes in the dominance rank and reproductive behavior of male bonnet macaques (Macaca radiate)". Animal Behaviour 32: 994–1003. doi:10.1016/s0003-3472(84)80212-2.
- Delpietro, H.A.; Russo, R.G. (2002). "Observations of the common vampire bat (Desmodus rotundus) and the hairy-legged vampire bat (Diphylla ecaudata) in captivity". Mammalian Biology 67 (2): 65–78. doi:10.1078/1616-5047-00011.
- Kleiman, Devra G. (1977). "Monogamy in Mammals". The Quarterly Review of Biology 52 (1): 39–69. PMID 857268.
- Holland, B.; Rice, W. R. (1998). "Perspective: Chase-Away Sexual Selection: Antagonistic Seduction vs. Resistance" (PDF). Evolution 52: 1–7.
- Clutton-Brock, T. H. (1989). "Review Lecture: Mammalian Mating Systems". Proceedings of the Royal Society of London. Series B, Biological Sciences 236 (1285): 339–372. doi:10.1098/rspb.1989.0027.
- Leboeuf, J. B. (1972). "Sexual behavior in the northern elephant seal Mirounga angustirostris". Behaviour 41 (1): 1–26. doi:10.1163/156853972X00167. JSTOR 4533425. PMID 5062032.
- Boness, D. J.; Bowen, D.; Buhleier, B. M.; Marshall, G. J. (2006). "Mating tactics and mating system of an aquatic-mating pinniped: the harbor seal, Phoca vitulina" (PDF). Behavioral Ecology and Sociobiology 61: 119–30. doi:10.1007/s00265-006-0242-9.
- "Leg and foot". Archived from the original on 2008-04-04. Retrieved 3 August 2008.
- Walker, Warren F.; Homberger, Dominique G. (1998). Anatomy and Dissection of the Fetal Pig (5 ed.). New York: W. H. Freeman and Company. p. 3. ISBN 978-0-7167-2637-1. OCLC 40576267.
- Orr, CM. (2005). "Knuckle-walking anteater: a convergence test of adaptation for purported knuckle-walking features of African Hominidae". Am. J. Phys. Anthropol. 128 (3): 639–58. doi:10.1002/ajpa.20192. PMID 15861420.
- Fish, FE; Frappell, PB; Baudinette, RV; MacFarlane, PM (2001). "Energetics of terrestrial locomotion of the platypus Ornithorhynchus anatinus" (PDF). The Journal of Experimental Biology 204 (Pt 4): 797–803. PMID 11171362.
- Dagg, Anne I. (1973). "Gaits in Mammals". Mammal Review 3 (4): 135–154. doi:10.1111/j.1365-2907.1973.tb00179.x.
- Roberts, Tristan D. M. (1995). Understanding Balance: The Mechanics of Posture and Locomotion. San Diego: Nelson Thornes. p. 211. ISBN 978-1-56593-416-0. OCLC 33167785.
- Cartmill, M. (1985). Climbing. In Functional Vertebrate Morphology, eds. M. Hildebrand D. M. Bramble K. F. Liem and D. B. Wake), pp. 73–88. Cambridge: Belknap Press.
- Emerson, S.B., & Koehl, M.A.R. (1990). "The interaction of behavioral and morphological change in the evolution of a novel locomotor type: 'Flying' frogs." Evolution, 44(8), 1931-1946.
- A. Barba, Lorena (October 2011). "Bats – the only flying mammals". Bio-Aerial Locomotion. Retrieved 20 May 2016.
- "Bats In Flight Reveal Unexpected Aerodynamics". ScienceDaily. 2007. Retrieved July 12, 2016.
- Hedenström, Anders; Johansson, L. C. (2015). "Bat flight: aerodynamics, kinematics and flight morphology" (PDF). Journal of Experimental Biology 218: 653–663. doi:10.1242/jeb.031203.
- "Bats save energy by drawing in wings on upstroke". ScienceDaily. 2012. Retrieved July 12, 2016.
- Taschek, Karen (2008). Hanging with Bats: Ecobats, Vampires, and Movie Stars. Albuquerque, New Mexico: University of New Mexico Press. p. 14. ISBN 978-0-8263-4403-8. OCLC 191258477.
- Sterbing-D'Angeloa, Susanne; Chadhab, Mohit; Chiuc, Chen; Falkc, Ben; Xianc, Wei; Barceloc, Janna; Zookd, John M.; Mossa, Cynthia F. (2011). "Bat wing sensors support flight control" (PDF). Proceedings of the National Academy of Sciences of the United States of America 108 (27): 11291–11296. doi:10.1073/pnas.1018740108.
- Shimer, H. W. (1903). "Adaptations to Aquatic, Arboreal, Fossorial and Cursorial Habits in Mammals. III. Fossorial Adaptations". The American Naturalist 37 (444): 819–825. doi:10.1086/278368.
- Perry, D. A. (1949). "The anatomical basis of swimming in Whales". Journal of Zoology 119 (1): 49–60. doi:10.1111/j.1096-3642.1949.tb00866.x.
- Fish, F. E.; Hui, C. A. (1991). "Dolphin swimming — a review" (PDF). Mammal Review 21 (4): 181–195. doi:10.1111/j.1365-2907.1991.tb00292.x.
- Marsh, Helene (1989). "Chapter 57: Dugongidae". Fauna of Australia (PDF) 1. Canberra: Australian Government Publications. ISBN 978-0-644-06056-1. OCLC 27492815.
- Berta, pp. 62–64.
- Fish, F. E. (2003). "Maneuverability by the sea lion Zalophus californianus: Turning performance of an unstable body design". Journal of Experimental Biology 206 (4): 667–74. doi:10.1242/jeb.00144. PMID 12517984.
- Riedman, M. (1990). The Pinnipeds: Seals, Sea Lions, and Walruses. University of California Press. ISBN 978-0-520-06497-3. OCLC 19511610.
- Fish, F. E. (1996). "Transitions from drag-based to lift-based propulsion in mammalian swimming". Integrative and Comparative Biology 36 (6): 628–41. doi:10.1093/icb/36.6.628.
- Fish, Frank E. (2000). "Biomechanics and Energetics in Aquatic and Semiaquatic Mammals: Platypus to Whale" (PDF). Physiological and Biochemical Zoology 73 (6): 683–698. PMID 11121343.
- Eltringham, S. K. (1999). "Anatomy and Physiology". The Hippos. London: T & AD Poyser Ltd. p. 8. ISBN 978-0-8566-1131-5. OCLC 42274422.
- "Hippopotamus Hippopotamus amphibius". National Geographic. Archived from the original on 2014-11-25. Retrieved 30 April 2016.
- Price, E (2008). Principles and applications of domestic animal behavior: an introductory text. Sacramento: Cambridge University Press. ISBN 978-1-84593-398-2. OCLC 226038028.
- Taupitz, Jochen; Weschka, Marion (2009). CHIMBRIDS - Chimeras and Hybrids in Comparative European and International Research. Heidelberg: Springer. p. 13. ISBN 978-3-540-93869-9. OCLC 495479133.
- Chambers, Steven M.; Fain, Steven R.; Fazio, Bud; Amaral, Michael (2012). "An account of the taxonomy of North American wolves from morphological and genetic analyses". North American Fauna 77: 2. doi:10.3996/nafa.77.0001.
- van Vuure, T. (2005). Retracing the Aurochs – History, Morphology and Ecology of an extinct wild Ox. Pensoft Publishers. ISBN 978-954-642-235-4. OCLC 940879282.
- Brown W.M. (2001). "Natural selection of mammalian brain components". Trends in Ecology and Evolution 16 (9): 471–473. doi:10.1016/S0169-5347(01)02246-7.
- Jaffa, Khalaf-von; Taher, Norman Ali Bassam Ali (2006). "Mammalia Palaestina: The Mammals of Palestine". The Palestinian Biological Bulletin (55): 1–46.
- McKenna, Malcolm C.; Bell, Susan K. (1997). Classification of Mammals Above the Species Level. New York: Columbia University Press. ISBN 978-0-231-11013-6. OCLC 37345734.
- Nowak, Ronald M. (1999). Walker's mammals of the world (6 ed.). Baltimore: Johns Hopkins University Press. ISBN 978-0-8018-5789-8. OCLC 937619124.
- Simpson, George Gaylord (1945). "The principles of classification and a classification of mammals". Bulletin of the American Museum of Natural History 85: 1–350.
- Murphy, William J.; Eizirik, Eduardo; O'Brien, Stephen J.; Madsen, Ole; Scally, Mark; Douady, Christophe J.; Teeling, Emma; Ryder, Oliver A.; Stanhope, Michael J.; de Jong, Wilfried W.; Springer, Mark S. (2001). "Resolution of the Early Placental Mammal Radiation Using Bayesian Phylogenetics". Science 294 (5550): 2348–2351. doi:10.1126/science.1067179.
- Springer, Mark S.; Stanhope, Michael J.; Madsen, Ole; de Jong, Wilfried W. (2004). "Molecules consolidate the placental mammal tree" (PDF). Trends in Ecology and Evolution 19 (8): 430–438. doi:10.1016/j.tree.2004.05.006. PMID 16701301.
- Vaughan, Terry A.; Ryan, James M.; Capzaplewski, Nicholas J. (2000). Mammalogy (4 ed.). Fort Worth, Texas: Saunders College Publishing. ISBN 978-0-03-025034-7. OCLC 42285340.
- Ole Kriegs, Jan; Churakov, Gennady; Kiefmann, Martin; Jordan, Ursula; Brosius, Juergen; Schmitz, Juergen (2006). "Retroposed Elements as Archives for the Evolutionary History of Placental Mammals". PLoS Biol 4 (4): e91. doi:10.1371/journal.pbio.0040091. PMC 1395351. PMID 16515367.
- MacDonald, David W.; Norris, Sasha (2006). The Encyclopedia of Mammals (3 ed.). London: Brown Reference Group. ISBN 978-0-681-45659-4. OCLC 74900519.
Find more about
at Wikipedia's sister projects
|Definitions from Wiktionary|
|Media from Commons|
|News from Wikinews|
|Quotations from Wikiquote|
|Texts from Wikisource|
|Textbooks from Wikibooks|
|Learning resources from Wikiversity|
|Data from Wikidata|
|Taxonomy from Wikispecies|
|External identifiers for Mammalia|
|Encyclopedia of Life||1642|
|Also found in: Wikispecies, Arctos|
- BBC Wildlife Finder – video clips from the BBC's natural history archive
- Biodiversitymapping.org – All mammal orders in the world with distribution maps
- Paleocene Mammals, a site covering the rise of the mammals, paleocene-mammals.de
- Evolution of Mammals, a brief introduction to early mammals, enchantedlearning.com
- Mammal Species, collection of information sheets about various mammal species, learnanimals.com
- European Mammal Atlas EMMA from Societas Europaea Mammalogica, European-mammals.org
- Marine Mammals of the World—An overview of all marine mammals, including descriptions, both fully aquatic and semi-aquatic, noaa.gov
- Mammalogy.org The American Society of Mammalogists was established in 1919 for the purpose of promoting the study of mammals, and this website includes a mammal image library