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This article is about the animal class. Mammal_sentence_0

For other uses, see Mammal (disambiguation). Mammal_sentence_1

"Mammalian" redirects here. Mammal_sentence_2

For the 2010 documentary film, see Mammalian (film). Mammal_sentence_3

"Mammalia" redirects here. Mammal_sentence_4

For the journal, see Mammalia (journal). Mammal_sentence_5



Temporal range: Late Triassic–Recent; 225 or 167–0 Ma See discussion of dates in text PreꞒ O S D C P T J K Pg NMammal_header_cell_0_0_0

Scientific classification MammaliaMammal_header_cell_0_1_0
Kingdom:Mammal_cell_0_2_0 AnimaliaMammal_cell_0_2_1
Phylum:Mammal_cell_0_3_0 ChordataMammal_cell_0_3_1
Superclass:Mammal_cell_0_4_0 TetrapodaMammal_cell_0_4_1
Clade:Mammal_cell_0_5_0 ReptiliomorphaMammal_cell_0_5_1
Clade:Mammal_cell_0_6_0 AmniotaMammal_cell_0_6_1
Clade:Mammal_cell_0_7_0 SynapsidaMammal_cell_0_7_1
Clade:Mammal_cell_0_8_0 MammaliaformesMammal_cell_0_8_1
Class:Mammal_cell_0_9_0 Mammalia

Linnaeus, 1758Mammal_cell_0_9_1

Living subgroupsMammal_header_cell_0_10_0

Mammals (from Latin "breast") are a group of vertebrate animals constituting the class Mammalia (/məˈmeɪliə/), and characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or hair, and three middle ear bones. Mammal_sentence_6

These characteristics distinguish them from reptiles and birds, from which they diverged in the late Carboniferous, approximately 300 million years ago. Mammal_sentence_7

Around 6,400 extant species of mammals have been described. Mammal_sentence_8

The largest orders are the rodents, bats and Eulipotyphla (hedgehogs, moles, shrews, and others). Mammal_sentence_9

The next three are the Primates (apes including humans, monkeys, and others), the Artiodactyla (cetaceans and even-toed ungulates), and the Carnivora (cats, dogs, seals, and others). Mammal_sentence_10

In terms of cladistics, which reflects evolutionary history, mammals are the only living members of the Synapsida; this clade, together with Sauropsida (reptiles and birds), constitutes the larger Amniota clade. Mammal_sentence_11

The early synapsid mammalian ancestors were sphenacodont pelycosaurs, a group that included the non-mammalian Dimetrodon. Mammal_sentence_12

At the end of the Carboniferous period around 300 million years ago, this group diverged from the sauropsid line that led to today's reptiles and birds. Mammal_sentence_13

The line following the stem group Sphenacodontia split into several diverse groups of non-mammalian synapsids—sometimes incorrectly referred to as mammal-like reptiles—before giving rise to Therapsida in the Early Permian period. Mammal_sentence_14

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 the dominant terrestrial animal group from 66 million years ago to the present. Mammal_sentence_15

The basic body type is quadruped, and most mammals use their four extremities for terrestrial locomotion; but in some, the extremities are adapted for life at sea, in the air, in trees, underground, or on two legs. Mammal_sentence_16

Mammals range in size from the 30–40 mm (1.2–1.6 in) bumblebee bat to the 30 m (98 ft) blue whale—possibly the largest animal to have ever lived. Mammal_sentence_17

Maximum lifespan varies from two years for the shrew to 211 years for the bowhead whale. Mammal_sentence_18

All modern mammals give birth to live young, except the five species of monotremes, which are egg-laying mammals. Mammal_sentence_19

The most species-rich group of mammals, the cohort called placentals, have a placenta, which enables the feeding of the fetus during gestation. Mammal_sentence_20

Most mammals are intelligent, with some possessing large brains, self-awareness, and tool use. Mammal_sentence_21

Mammals can communicate and vocalize in several ways, including the production of ultrasound, scent-marking, alarm signals, singing, and echolocation. Mammal_sentence_22

Mammals can organize themselves into fission-fusion societies, harems, and hierarchies—but can also be solitary and territorial. Mammal_sentence_23

Most mammals are polygynous, but some can be monogamous or polyandrous. Mammal_sentence_24

Domestication of many types of mammals by humans played a major role in the Neolithic revolution, and resulted in farming replacing hunting and gathering as the primary source of food for humans. Mammal_sentence_25

This led to a major restructuring of human societies from nomadic to sedentary, with more co-operation among larger and larger groups, and ultimately the development of the first civilizations. Mammal_sentence_26

Domesticated mammals provided, and continue to provide, power for transport and agriculture, as well as food (meat and dairy products), fur, and leather. Mammal_sentence_27

Mammals are also hunted and raced for sport, and are used as model organisms in science. Mammal_sentence_28

Mammals have been depicted in art since Palaeolithic times, and appear in literature, film, mythology, and religion. Mammal_sentence_29

Decline in numbers and extinction of many mammals is primarily driven by human poaching and habitat destruction, primarily deforestation. Mammal_sentence_30

Classification Mammal_section_0

Main article: Mammal classification Mammal_sentence_31

See also: List of placental mammals, List of monotremes and marsupials, List of mammal genera, and List of mammal species Mammal_sentence_32

Mammal classification has been through several iterations since Carl Linnaeus initially defined the class. Mammal_sentence_33

No classification system is universally accepted; McKenna & Bell (1997) and Wilson & Reader (2005) provide useful recent compendiums. Mammal_sentence_34

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. Mammal_sentence_35

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. Mammal_sentence_36

Though field work gradually made Simpson's classification outdated, it remains the closest thing to an official classification of mammals. Mammal_sentence_37

Most mammals, including the six most species-rich orders, belong to the placental group. Mammal_sentence_38

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. Mammal_sentence_39

The next three biggest orders, depending on the biological classification scheme used, are the Primates including the apes, monkeys and lemurs; the Cetartiodactyla including whales and even-toed ungulates; and the Carnivora which includes cats, dogs, weasels, bears, seals and allies. Mammal_sentence_40

According to Mammal Species of the World, 5,416 species were identified in 2006. Mammal_sentence_41

These were grouped into 1,229 genera, 153 families and 29 orders. Mammal_sentence_42

In 2008, the International Union for Conservation of Nature (IUCN) completed a five-year Global Mammal Assessment for its IUCN Red List, which counted 5,488 species. Mammal_sentence_43

According to research published in the Journal of Mammalogy in 2018, the number of recognized mammal species is 6,495 including 96 recently extinct. Mammal_sentence_44

Definitions Mammal_section_1

The word "" is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from the Latin ("teat, pap"). Mammal_sentence_45

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. Mammal_sentence_46

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. Mammal_sentence_47

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. Mammal_sentence_48

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 million years ago in the Middle Jurassic, this is a reasonable estimate for the appearance of the crown group. Mammal_sentence_49

T. S. Kemp has provided a more traditional definition: "Synapsids that possess a dentarysquamosal 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. Mammal_sentence_50

The earliest known synapsid satisfying Kemp's definitions is Tikitherium, dated Ma, so the appearance of mammals in this broader sense can be given this Late Triassic date. Mammal_sentence_51

McKenna/Bell classification Mammal_section_2

See also: Mammal_classification § McKenna/Bell classification Mammal_sentence_52

In 1997, the mammals were comprehensively revised by Malcolm C. McKenna and Susan K. Bell, which has resulted in the McKenna/Bell classification. Mammal_sentence_53

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. Mammal_sentence_54

The authors worked together as paleontologists at the American Museum of Natural History, New York. Mammal_sentence_55

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. Mammal_sentence_56

In the following list, extinct groups are labelled with a dagger (†). Mammal_sentence_57

Class Mammalia Mammal_sentence_58


Molecular classification of placentals Mammal_section_3

As of the early 21st century, molecular studies based on DNA analysis have suggested new relationships among mammal families. Mammal_sentence_59

Most of these findings have been independently validated by retrotransposon presence/absence data. Mammal_sentence_60

Classification systems based on molecular studies reveal three major groups or lineages of placental mammals—Afrotheria, Xenarthra and Boreoeutheria—which diverged in the Cretaceous. Mammal_sentence_61

The relationships between these three lineages is contentious, and all three possible hypotheses have been proposed with respect to which group is basal. Mammal_sentence_62

These hypotheses are Atlantogenata (basal Boreoeutheria), Epitheria (basal Xenarthra) and Exafroplacentalia (basal Afrotheria). Mammal_sentence_63

Boreoeutheria in turn contains two major lineages—Euarchontoglires and Laurasiatheria. Mammal_sentence_64

Estimates for the divergence times between these three placental groups range from 105 to 120 million years ago, depending on the type of DNA used (such as nuclear or mitochondrial) and varying interpretations of paleogeographic data. Mammal_sentence_65

The cladogram above is based on Tarver et al. Mammal_sentence_66

(2016) Mammal_sentence_67

Group I: Superorder Afrotheria Mammal_sentence_68


Group II: Superorder Xenarthra Mammal_sentence_69


  • Order Pilosa: sloths and anteaters (neotropical)Mammal_item_2_32
  • Order Cingulata: armadillos and extinct relatives (Americas)Mammal_item_2_33

Group III: Magnaorder Boreoeutheria Mammal_sentence_70


Evolution Mammal_section_4

Main article: Evolution of mammals Mammal_sentence_71

Origins Mammal_section_5

Synapsida, a clade that contains mammals and their extinct relatives, originated during the Pennsylvanian subperiod (~323 million to ~300 million years ago), when they split from reptilian and avian lineages. Mammal_sentence_72

Crown group mammals evolved from earlier mammaliaforms during the Early Jurassic. Mammal_sentence_73

The cladogram takes Mammalia to be the crown group. Mammal_sentence_74

Evolution from amniotes Mammal_section_6

The first fully terrestrial vertebrates were amniotes. Mammal_sentence_75

Like their amphibious tetrapod predecessors, they had lungs and limbs. Mammal_sentence_76

Amniotic eggs, however, have internal membranes that allow the developing embryo to breathe but keep water in. Mammal_sentence_77

Hence, amniotes can lay eggs on dry land, while amphibians generally need to lay their eggs in water. Mammal_sentence_78

The first amniotes apparently arose in the Pennsylvanian subperiod of the Carboniferous. Mammal_sentence_79

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. Mammal_sentence_80

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 and dinosaurs (including birds). Mammal_sentence_81

Synapsids have a single hole (temporal fenestra) low on each side of the skull. Mammal_sentence_82

One synapsid group, the pelycosaurs, included the largest and fiercest animals of the early Permian. Mammal_sentence_83

Nonmammalian synapsids are sometimes (inaccurately) called "mammal-like reptiles". Mammal_sentence_84

Therapsids, a group of synapsids, descended from pelycosaurs in the Middle Permian, about 265 million years ago, and became the dominant land vertebrates. Mammal_sentence_85

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. Mammal_sentence_86

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. Mammal_sentence_87

Those stages were characterized by: Mammal_sentence_88


  • The gradual development of a bony secondary palate.Mammal_item_4_53
  • 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.Mammal_item_4_54
  • 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).Mammal_item_4_55

First mammals Mammal_section_7

The Permian–Triassic extinction event about 252 million years ago, which was a prolonged event due to the accumulation of several extinction pulses, ended the dominance of carnivorous therapsids. Mammal_sentence_89

In the early Triassic, most medium to large land carnivore niches were taken over by archosaurs which, over an extended period (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. Mammal_sentence_90

By the Jurassic, the dinosaurs had come to dominate the large terrestrial herbivore niches as well. Mammal_sentence_91

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. Mammal_sentence_92

They expanded out of their nocturnal insectivore niche from the mid-Jurassic onwards; The Jurassic Castorocauda, for example, was a close relative of true mammals that had adaptations for swimming, digging and catching fish. Mammal_sentence_93

Most, if not all, are thought to have remained nocturnal (the nocturnal bottleneck), accounting for much of the typical mammalian traits. Mammal_sentence_94

The majority of the mammal species that existed in the Mesozoic Era were multituberculates, eutriconodonts and spalacotheriids. Mammal_sentence_95

The earliest known metatherian is Sinodelphys, found in 125 million-year-old Early Cretaceous shale in China's northeastern Liaoning Province. Mammal_sentence_96

The fossil is nearly complete and includes tufts of fur and imprints of soft tissues. Mammal_sentence_97

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. Mammal_sentence_98

A later eutherian relative, 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. Mammal_sentence_99

In particular, the epipubic bones extend forwards from the pelvis. Mammal_sentence_100

These are not found in any modern placental, but they are found in marsupials, monotremes, other nontherian mammals and Ukhaatherium, an early Cretaceous animal in the eutherian order Asioryctitheria. Mammal_sentence_101

This also applies to the multituberculates. Mammal_sentence_102

They are apparently an ancestral feature, which subsequently disappeared in the placental lineage. Mammal_sentence_103

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. Mammal_sentence_104

A narrow pelvic outlet indicates that the young were very small at birth and therefore pregnancy was short, as in modern marsupials. Mammal_sentence_105

This suggests that the placenta was a later development. Mammal_sentence_106

One of the earliest known monotremes was Teinolophos, which lived about 120 million years ago in Australia. Mammal_sentence_107

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. Mammal_sentence_108

Earliest appearances of features Mammal_section_8

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. Mammal_sentence_109

The earliest clear evidence of hair or fur is in fossils of Castorocauda and Megaconus, from 164 million years ago in the mid-Jurassic. Mammal_sentence_110

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. Mammal_sentence_111

Popular sources, nevertheless, continue to attribute whiskers to Thrinaxodon. Mammal_sentence_112

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. Mammal_sentence_113

When endothermy first appeared in the evolution of mammals is uncertain, though it is generally agreed to have first evolved in non-mammalian therapsids. Mammal_sentence_114

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. Mammal_sentence_115

Likewise, some modern therians like afrotheres and xenarthrans have secondarily developed lower body temperatures. Mammal_sentence_116

The evolution of erect limbs in mammals is incomplete—living and fossil monotremes have sprawling limbs. Mammal_sentence_117

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. Mammal_sentence_118

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. Mammal_sentence_119

They are omnipresent in non-placental mammaliformes, though Megazostrodon and Erythrotherium appear to have lacked them. Mammal_sentence_120

It has been suggested that the original function of lactation (milk production) was to keep eggs moist. Mammal_sentence_121

Much of the argument is based on monotremes, the egg-laying mammals. Mammal_sentence_122

Rise of the mammals Mammal_section_9

Therian mammals took over the medium- to large-sized ecological niches in the Cenozoic, after the Cretaceous–Paleogene extinction event approximately 66 million years ago emptied ecological space once filled by non-avian dinosaurs and other groups of reptiles, as well as various other mammal groups, and underwent an exponential increase in body size (megafauna). Mammal_sentence_123

Then mammals diversified very quickly; both birds and mammals show an exponential rise in diversity. Mammal_sentence_124

For example, the earliest known bat dates from about 50 million years ago, only 16 million years after the extinction of the non-avian dinosaurs. Mammal_sentence_125

Molecular phylogenetic studies initially suggested 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. Mammal_sentence_126

However, no placental fossils have been found from before the end of the Cretaceous. Mammal_sentence_127

The earliest undisputed fossils of placentals comes from the early Paleocene, after the extinction of the non-avian dinosaurs. Mammal_sentence_128

In particular, scientists have identified an early Paleocene animal named Protungulatum donnae as one of the first placental mammals. Mammal_sentence_129

however it has been reclassified as a non-placental eutherian. Mammal_sentence_130

Recalibrations of genetic and morphological diversity rates have suggested a Late Cretaceous origin for placentals, and a Paleocene origin for most modern clades. Mammal_sentence_131

The earliest known ancestor of primates is Archicebus achilles from around 55 million years ago. Mammal_sentence_132

This tiny primate weighed 20–30 grams (0.7–1.1 ounce) and could fit within a human palm. Mammal_sentence_133

Anatomy Mammal_section_10

Distinguishing features Mammal_section_11

Living mammal species can be identified by the presence of sweat glands, including those that are specialized to produce milk to nourish their young. Mammal_sentence_134

In classifying fossils, however, other features must be used, since soft tissue glands and many other features are not visible in fossils. Mammal_sentence_135

Many traits shared by all living mammals appeared among the earliest members of the group: Mammal_sentence_136


  • 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).Mammal_item_5_56
  • 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.Mammal_item_5_57
  • Tooth replacement – Teeth can be replaced once (diphyodonty) or (as in toothed whales and murid rodents) not at all (monophyodonty). Elephants, manatees, and kangaroos continually grow new teeth throughout their life (polyphyodonty).Mammal_item_5_58
  • 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.Mammal_item_5_59
  • 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.Mammal_item_5_60

For the most part, these characteristics were not present in the Triassic ancestors of the mammals. Mammal_sentence_137

Nearly all mammaliaforms possess an epipubic bone, the exception being modern placentals. Mammal_sentence_138

Sexual dimorphism Mammal_section_12

On average, male mammals are larger than females, with males being at least 10% larger than females in over 45% of investigated species. Mammal_sentence_139

Most mammalian orders are also exhibit male-biased sexual dimorphism, although some orders do not show any bias or are significantly female-biased (Lagomorpha). Mammal_sentence_140

Sexual size dimorphism increases with body size across mammals (Rensch’s rule), suggesting that there are parallel selection pressures on both male and female size. Mammal_sentence_141

Male-biased dimorphism relates to sexual selection on males through male–male competition for females, as there is a positive correlation between the degree of sexual selection, as indicated by mating systems, and the degree of male-biased size dimorphism. Mammal_sentence_142

The degree of sexual selection is also positively correlated with male and female size across mammals. Mammal_sentence_143

Further, a parallel selection pressure on female mass is identified in that age at weaning is significantly higher in more polygynous species, even when correcting for body mass. Mammal_sentence_144

Also, reproductive rate is lower for larger females, indicating that fecundity selection selects for smaller females in mammals. Mammal_sentence_145

Although these patterns hold across mammals as a whole, there is considerable variation across orders. Mammal_sentence_146

Biological systems Mammal_section_13

Main article: Biological system Mammal_sentence_147

The majority of mammals have seven cervical vertebrae (bones in the neck)\. Mammal_sentence_148

The exceptions are the manatee and the two-toed sloth, which have six, and the three-toed sloth which has nine. Mammal_sentence_149

All mammalian brains possess a neocortex, a brain region unique to mammals. Mammal_sentence_150

Placental brains have a corpus callosum, unlike monotremes and marsupials. Mammal_sentence_151

The lungs of mammals are spongy and honeycombed. Mammal_sentence_152

Breathing is mainly achieved with the diaphragm, which divides the thorax from the abdominal cavity, forming a dome convex to the thorax. Mammal_sentence_153

Contraction of the diaphragm flattens the dome, increasing the volume of the lung cavity. Mammal_sentence_154

Air enters through the oral and nasal cavities, and travels through the larynx, trachea and bronchi, and expands the alveoli. Mammal_sentence_155

Relaxing the diaphragm has the opposite effect, decreasing the volume of the lung cavity, causing air to be pushed out of the lungs. Mammal_sentence_156

During exercise, the abdominal wall contracts, increasing pressure on the diaphragm, which forces air out quicker and more forcefully. Mammal_sentence_157

The rib cage is able to expand and contract the chest cavity through the action of other respiratory muscles. Mammal_sentence_158

Consequently, air is sucked into or expelled out of the lungs, always moving down its pressure gradient. Mammal_sentence_159

This type of lung is known as a bellows lung due to its resemblance to blacksmith bellows. Mammal_sentence_160

The mammalian heart has four chambers, two upper atria, the receiving chambers, and two lower ventricles, the discharging chambers. Mammal_sentence_161

The heart has four valves, which separate its chambers and ensures blood flows in the correct direction through the heart (preventing backflow). Mammal_sentence_162

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. Mammal_sentence_163

Blood flows nearly continuously back into the atrium, which acts as the receiving chamber, and from here through an opening into the left ventricle. Mammal_sentence_164

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. Mammal_sentence_165

The heart also requires nutrients and oxygen found in blood like other muscles, and is supplied via coronary arteries. Mammal_sentence_166

The integumentary system (skin) is made up of three layers: the outermost epidermis, the dermis and the hypodermis. Mammal_sentence_167

The epidermis is typically 10 to 30 cells thick; its main function is to provide a waterproof layer. Mammal_sentence_168

Its outermost cells are constantly lost; its bottommost cells are constantly dividing and pushing upward. Mammal_sentence_169

The middle layer, the dermis, is 15 to 40 times thicker than the epidermis. Mammal_sentence_170

The dermis is made up of many components, such as bony structures and blood vessels. Mammal_sentence_171

The hypodermis is made up of adipose tissue, which stores lipids and provides cushioning and insulation. Mammal_sentence_172

The thickness of this layer varies widely from species to species; marine mammals require a thick hypodermis (blubber) for insulation, and right whales have the thickest blubber at 20 inches (51 cm). Mammal_sentence_173

Although other animals have features such as whiskers, feathers, setae, or cilia that superficially resemble it, no animals other than mammals have hair. Mammal_sentence_174

It is a definitive characteristic of the class, though some mammals have very little. Mammal_sentence_175

Herbivores have developed a diverse range of physical structures to facilitate the consumption of plant material. Mammal_sentence_176

To break up intact plant tissues, mammals have developed teeth structures that reflect their feeding preferences. Mammal_sentence_177

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. Mammal_sentence_178

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. Mammal_sentence_179

Most carnivorous mammals have carnassialiforme teeth (of varying length depending on diet), long canines and similar tooth replacement patterns. Mammal_sentence_180

The stomach of even-toed ungulates (Artiodactyla) is divided into four sections: the rumen, the reticulum, the omasum and the abomasum (only ruminants have a rumen). Mammal_sentence_181

After the plant material is consumed, it is mixed with saliva in the rumen and reticulum and separates into solid and liquid material. Mammal_sentence_182

The solids lump together to form a bolus (or cud), and is regurgitated. Mammal_sentence_183

When the bolus enters the mouth, the fluid is squeezed out with the tongue and swallowed again. Mammal_sentence_184

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. Mammal_sentence_185

Perissodactyls, in contrast to the ruminants, store digested food that has left the stomach in an enlarged cecum, where it is fermented by bacteria. Mammal_sentence_186

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. Mammal_sentence_187

The caecum is either absent or short and simple, and the large intestine is not sacculated or much wider than the small intestine. Mammal_sentence_188

The mammalian excretory system involves many components. Mammal_sentence_189

Like most other land animals, mammals are ureotelic, and convert ammonia into urea, which is done by the liver as part of the urea cycle. Mammal_sentence_190

Bilirubin, a waste product derived from blood cells, is passed through bile and urine with the help of enzymes excreted by the liver. Mammal_sentence_191

The passing of bilirubin via bile through the intestinal tract gives mammalian feces a distinctive brown coloration. Mammal_sentence_192

Distinctive features of the mammalian kidney include the presence of the renal pelvis and renal pyramids, and of a clearly distinguishable cortex and medulla, which is due to the presence of elongated loops of Henle. Mammal_sentence_193

Only the mammalian kidney has a bean shape, although there are some exceptions, such as the multilobed reniculate kidneys of pinnipeds, cetaceans and bears. Mammal_sentence_194

Most adult placental mammals have no remaining trace of the cloaca. Mammal_sentence_195

In the embryo, the embryonic cloaca divides into a posterior region that becomes part of the anus, and an anterior region that has different fates depending on the sex of the individual: in females, it develops into the vestibule that receives the urethra and vagina, while in males it forms the entirety of the penile urethra. Mammal_sentence_196

However, the tenrecs, golden moles, and some shrews retain a cloaca as adults. Mammal_sentence_197

In marsupials, the genital tract is separate from the anus, but a trace of the original cloaca does remain externally. Mammal_sentence_198

Monotremes, which translates from Greek into "single hole", have a true cloaca. Mammal_sentence_199

Sound production Mammal_section_14

As in all other tetrapods, mammals have a larynx that can quickly open and close to produce sounds, and a supralaryngeal vocal tract which filters this sound. Mammal_sentence_200

The lungs and surrounding musculature provide the air stream and pressure required to phonate. Mammal_sentence_201

The larynx controls the pitch and volume of sound, but the strength the lungs exert to exhale also contributes to volume. Mammal_sentence_202

More primitive mammals, such as the echidna, can only hiss, as sound is achieved solely through exhaling through a partially closed larynx. Mammal_sentence_203

Other mammals phonate using vocal folds, as opposed to the vocal cords seen in birds and reptiles. Mammal_sentence_204

The movement or tenseness of the vocal folds can result in many sounds such as purring and screaming. Mammal_sentence_205

Mammals can change the position of the larynx, allowing them to breathe through the nose while swallowing through the mouth, and to form both oral and nasal sounds; nasal sounds, such as a dog whine, are generally soft sounds, and oral sounds, such as a dog bark, are generally loud. Mammal_sentence_206

Some mammals have a large larynx and thus a low-pitched voice, namely the hammer-headed bat (Hypsignathus monstrosus) where the larynx can take up the entirety of the thoracic cavity while pushing the lungs, heart, and trachea into the abdomen. Mammal_sentence_207

Large vocal pads can also lower the pitch, as in the low-pitched roars of big cats. Mammal_sentence_208

The production of infrasound is possible in some mammals such as the African elephant (Loxodonta spp.) and baleen whales. Mammal_sentence_209

Small mammals with small larynxes have the ability to produce ultrasound, which can be detected by modifications to the middle ear and cochlea. Mammal_sentence_210

Ultrasound is inaudible to birds and reptiles, which might have been important during the Mesozoic, when birds and reptiles were the dominant predators. Mammal_sentence_211

This private channel is used by some rodents in, for example, mother-to-pup communication, and by bats when echolocating. Mammal_sentence_212

Toothed whales also use echolocation, but, as opposed to the vocal membrane that extends upward from the vocal folds, they have a melon to manipulate sounds. Mammal_sentence_213

Some mammals, namely the primates, have air sacs attached to the larynx, which may function to lower the resonances or increase the volume of sound. Mammal_sentence_214

The vocal production system is controlled by the cranial nerve nuclei in the brain, and supplied by the recurrent laryngeal nerve and the superior laryngeal nerve, branches of the vagus nerve. Mammal_sentence_215

The vocal tract is supplied by the hypoglossal nerve and facial nerves. Mammal_sentence_216

Electrical stimulation of the periaqueductal gray (PEG) region of the mammalian midbrain elicit vocalizations. Mammal_sentence_217

The ability to learn new vocalizations is only exemplified in humans, seals, cetaceans, elephants and possibly bats; in humans, this is the result of a direct connection between the motor cortex, which controls movement, and the motor neurons in the spinal cord. Mammal_sentence_218

Fur Mammal_section_15

Main article: Fur Mammal_sentence_219

The primary function of the fur of mammals is thermoregulation. Mammal_sentence_220

Others include protection, sensory purposes, waterproofing, and camouflage. Mammal_sentence_221

Different types of fur serve different purposes: Mammal_sentence_222


  • Definitive – which may be shed after reaching a certain lengthMammal_item_6_61
  • Vibrissae – sensory hairs, most commonly whiskersMammal_item_6_62
  • Pelage – guard hairs, under-fur, and awn hairMammal_item_6_63
  • Spines – stiff guard hair used for defense (such as in porcupines)Mammal_item_6_64
  • Bristles – long hairs usually used in visual signals. (such as a lion's mane)Mammal_item_6_65
  • Velli – often called "down fur" which insulates newborn mammalsMammal_item_6_66
  • Wool – long, soft and often curlyMammal_item_6_67

Thermoregulation Mammal_section_16

Hair length is not a factor in thermoregulation: for example, some tropical mammals such as sloths have the same length of fur length as some arctic mammals but with less insulation; and, conversely, other tropical mammals with short hair have the same insulating value as arctic mammals. Mammal_sentence_223

The denseness of fur can increase an animal's insulation value, and arctic mammals especially have dense fur; for example, the musk ox has guard hairs measuring 30 cm (12 in) as well as a dense underfur, which forms an airtight coat, allowing them to survive in temperatures of −40 °C (−40 °F). Mammal_sentence_224

Some desert mammals, such as camels, use dense fur to prevent solar heat from reaching their skin, allowing the animal to stay cool; a camel's fur may reach 70 °C (158 °F) in the summer, but the skin stays at 40 °C (104 °F). Mammal_sentence_225

Aquatic mammals, conversely, trap air in their fur to conserve heat by keeping the skin dry. Mammal_sentence_226

Coloration Mammal_section_17

Mammalian coats are colored for a variety of reasons, the major selective pressures including camouflage, sexual selection, communication, and thermoregulation. Mammal_sentence_227

Coloration in both the hair and skin of mammals is mainly determined by the type and amount of melanin; eumelanins for brown and black colors and pheomelanin for a range of yellowish to reddish colors, giving mammals an earth tone. Mammal_sentence_228

Some mammals, like the mandrill, have more vibrant colors due to structural coloration. Mammal_sentence_229

Many sloths appear green because their fur hosts green algae; this may be a symbiotic relation that affords camouflage to the sloths. Mammal_sentence_230

Camouflage is a powerful influence in a large number of mammals, as it helps to conceal individuals from predators or prey. Mammal_sentence_231

In arctic and subarctic mammals such as the arctic fox (Alopex lagopus), collared lemming (Dicrostonyx groenlandicus), stoat (Mustela erminea), and snowshoe hare (Lepus americanus), seasonal color change between brown in summer and white in winter is driven largely by camouflage. Mammal_sentence_232

Some arboreal mammals, notably primates and marsupials, have shades of violet, green, or blue skin on parts of their bodies, indicating some distinct advantage in their largely arboreal habitat due to convergent evolution. Mammal_sentence_233

Aposematism, warning off possible predators, is the most likely explanation of the black-and-white pelage of many mammals which are able to defend themselves, such as in the foul-smelling skunk and the powerful and aggressive honey badger. Mammal_sentence_234

Coat color is sometimes sexually dimorphic, as in many primate species. Mammal_sentence_235

Differences in female and male coat color may indicate nutrition and hormone levels, important in mate selection. Mammal_sentence_236

Coat color may influence the ability to retain heat, depending on how much light is reflected. Mammal_sentence_237

Mammals with a darker colored coat can absorb more heat from solar radiation, and stay warmer, and some smaller mammals, such as voles, have darker fur in the winter. Mammal_sentence_238

The white, pigmentless fur of arctic mammals, such as the polar bear, may reflect more solar radiation directly onto the skin. Mammal_sentence_239

The dazzling black-and-white striping of zebras appear to provide some protection from biting flies. Mammal_sentence_240

Reproductive system Mammal_section_18

Main article: Mammalian reproduction Mammal_sentence_241

In male placentals, the penis is used both for urination and copulation. Mammal_sentence_242

Depending on the species, an erection may be fueled by blood flow into vascular, spongy tissue or by muscular action. Mammal_sentence_243

A penis may be contained in a prepuce when not erect, and some placentals also have a penis bone (baculum). Mammal_sentence_244

Marsupials typically have forked penises, while the echidna penis generally has four heads with only two functioning. Mammal_sentence_245

The testes of most mammals descend into the scrotum which is typically posterior to the penis but is often anterior in marsupials. Mammal_sentence_246

Female mammals generally have a clitoris, labia majora and labia minora on the outside, while the internal system contains paired oviducts, 1-2 uteri, 1-2 cervices and a vagina. Mammal_sentence_247

Marsupials have two lateral vaginas and a medial vagina. Mammal_sentence_248

The "vagina" of monotremes is better understood as a "urogenital sinus". Mammal_sentence_249

The uterine systems of placental mammals can vary between a duplex, were there are two uteri and cervices which open into the vagina, a bipartite, were two uterine horns have a single cervix that connects to the vagina, a bicornuate, which consists where two uterine horns that are connected distally but separate medially creating a Y-shape, and a simplex, which has a single uterus. Mammal_sentence_250

The ancestral condition for mammal reproduction is the birthing of relatively undeveloped, either through direct vivipary or a short period as soft-shelled eggs. Mammal_sentence_251

This is likely due to the fact that the torso could not expand due to the presence of epipubic bones. Mammal_sentence_252

The oldest demonstration of this reproductive style is with Kayentatherium, which produced undeveloped perinates, but at much higher litter sizes than any modern mammal, 38 specimens. Mammal_sentence_253

Most modern mammals are viviparous, giving birth to live young. Mammal_sentence_254

However, the five species of monotreme, the platypus and the four species of echidna, lay eggs. Mammal_sentence_255

The monotremes have a sex determination system different from that of most other mammals. Mammal_sentence_256

In particular, the sex chromosomes of a platypus are more like those of a chicken than those of a therian mammal. Mammal_sentence_257

Viviparous mammals are in the subclass Theria; those living today are in the marsupial and placental infraclasses. Mammal_sentence_258

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. Mammal_sentence_259

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. Mammal_sentence_260

Even non-placental eutherians probably reproduced this way. Mammal_sentence_261

The placentals give birth to relatively complete and developed young, usually after long gestation periods. Mammal_sentence_262

They get their name from the placenta, which connects the developing fetus to the uterine wall to allow nutrient uptake. Mammal_sentence_263

In placental mammals, the epipubic is either completely lost or converted into the baculum; allowing the torso to be able to expand and thus birth developed offspring. Mammal_sentence_264

The mammary glands of mammals are specialized to produce milk, the primary source of nutrition for newborns. Mammal_sentence_265

The monotremes branched early from other mammals and do not have the nipples seen in most mammals, but they do have mammary glands. Mammal_sentence_266

The young lick the milk from a mammary patch on the mother's belly. Mammal_sentence_267

Compared to placental mammals, the milk of marsupials changes greatly in both production rate and in nutrient composition, due to the underdeveloped young. Mammal_sentence_268

In addition, the mammary glands have more autonomy allowing them to supply separate milks to young at different development stages. Mammal_sentence_269

Lactose is the main sugar in placental mammal milk while monotreme and marsupial milk is dominated by oligosaccharides. Mammal_sentence_270

Weaning is the process in which a mammal becomes less dependent on their mother's milk and more on solid food. Mammal_sentence_271

Endothermy Mammal_section_19

Nearly all mammals are endothermic ("warm-blooded"). Mammal_sentence_272

Most mammals also have hair to help keep them warm. Mammal_sentence_273

Like birds, mammals can forage or hunt in weather and climates too cold for ectothermic ("cold-blooded") reptiles and insects. Mammal_sentence_274

Endothermy requires plenty of food energy, so mammals eat more food per unit of body weight than most reptiles. Mammal_sentence_275

Small insectivorous mammals eat prodigious amounts for their size. Mammal_sentence_276

A rare exception, the naked mole-rat produces little metabolic heat, so it is considered an operational poikilotherm. Mammal_sentence_277

Birds are also endothermic, so endothermy is not unique to mammals. Mammal_sentence_278

Species lifespan Mammal_section_20

See also: Life expectancy and Maximum life span Mammal_sentence_279

Among mammals, species maximum lifespan varies significantly (for example the shrew has a lifespan of two years, whereas the oldest bowhead whale is recorded to be 211 years). Mammal_sentence_280

Although the underlying basis for these lifespan differences is still uncertain, numerous studies indicate that the ability to repair DNA damage is an important determinant of mammalian lifespan. Mammal_sentence_281

In a 1974 study by Hart and Setlow, it was found that DNA excision repair capability increased systematically with species lifespan among seven mammalian species. Mammal_sentence_282

Species lifespan was observed to be robustly correlated with the capacity to recognize DNA double-strand breaks as well as the level of the DNA repair protein Ku80. Mammal_sentence_283

In a study of the cells from sixteen mammalian species, genes employed in DNA repair were found to be up-regulated in the longer-lived species. Mammal_sentence_284

The cellular level of the DNA repair enzyme poly ADP ribose polymerase was found to correlate with species lifespan in a study of 13 mammalian species. Mammal_sentence_285

Three additional studies of a variety of mammalian species also reported a correlation between species lifespan and DNA repair capability. Mammal_sentence_286

Locomotion Mammal_section_21

Main article: Animal locomotion Mammal_sentence_287

Terrestrial Mammal_section_22

Main article: Terrestrial locomotion Mammal_sentence_288

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. Mammal_sentence_289

Many mammals, such as cats and dogs, are digitigrade, walking on their toes, the greater stride length allowing more speed. Mammal_sentence_290

Digitigrade mammals are also often adept at quiet movement. Mammal_sentence_291

Some animals such as horses are unguligrade, walking on the tips of their toes. Mammal_sentence_292

This even further increases their stride length and thus their speed. Mammal_sentence_293

A few mammals, namely the great apes, are also known to walk on their knuckles, at least for their front legs. Mammal_sentence_294

Giant anteaters and platypuses are also knuckle-walkers. Mammal_sentence_295

Some mammals are bipeds, using only two limbs for locomotion, which can be seen in, for example, humans and the great apes. Mammal_sentence_296

Bipedal species have a larger field of vision than quadrupeds, conserve more energy and have the ability to manipulate objects with their hands, which aids in foraging. Mammal_sentence_297

Instead of walking, some bipeds hop, such as kangaroos and kangaroo rats. Mammal_sentence_298

Animals will use different gaits for different speeds, terrain and situations. Mammal_sentence_299

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. Mammal_sentence_300

Animals may also have unusual gaits that are used occasionally, such as for moving sideways or backwards. Mammal_sentence_301

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. Mammal_sentence_302

Mammals show a vast range of gaits, the order that they place and lift their appendages in locomotion. Mammal_sentence_303

Gaits can be grouped into categories according to their patterns of support sequence. Mammal_sentence_304

For quadrupeds, there are three main categories: walking gaits, running gaits and leaping gaits. Mammal_sentence_305

Walking is the most common gait, where some feet are on the ground at any given time, and found in almost all legged animals. Mammal_sentence_306

Running is considered to occur when at some points in the stride all feet are off the ground in a moment of suspension. Mammal_sentence_307

Arboreal Mammal_section_23

Main article: Arboreal locomotion Mammal_sentence_308

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 (swing between trees). Mammal_sentence_309

Many arboreal species, such as tree porcupines, silky anteaters, spider monkeys, and possums, use prehensile tails to grasp branches. Mammal_sentence_310

In the spider monkey, the tip of the tail has either a bare patch or adhesive pad, which provides increased friction. Mammal_sentence_311

Claws can be used to interact with rough substrates and reorient the direction of forces the animal applies. Mammal_sentence_312

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. Mammal_sentence_313

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. Mammal_sentence_314

Frictional gripping is used by primates, relying upon hairless fingertips. Mammal_sentence_315

Squeezing the branch between the fingertips generates frictional force that holds the animal's hand to the branch. Mammal_sentence_316

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. Mammal_sentence_317

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. Mammal_sentence_318

This allows the claws to hook into the rough surface of the bark, opposing the force of gravity. Mammal_sentence_319

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. Mammal_sentence_320

Size relating to weight affects gliding animals such as the sugar glider. Mammal_sentence_321

Some species of primate, bat and all species of sloth achieve passive stability by hanging beneath the branch. Mammal_sentence_322

Both pitching and tipping become irrelevant, as the only method of failure would be losing their grip. Mammal_sentence_323

Aerial Mammal_section_24

Main article: Aerial locomotion Mammal_sentence_324

Bats are the only mammals that can truly fly. Mammal_sentence_325

They fly through the air at a constant speed by moving their wings up and down (usually with some fore-aft movement as well). Mammal_sentence_326

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. Mammal_sentence_327

This generates a lift force vector pointing forwards and upwards, and a drag force vector pointing rearwards and upwards. Mammal_sentence_328

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. Mammal_sentence_329

The wings of bats are much thinner and consist of more bones than those of birds, allowing bats to maneuver more accurately and fly with more lift and less drag. Mammal_sentence_330

By folding the wings inwards towards their body on the upstroke, they use 35% less energy during flight than birds. Mammal_sentence_331

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. Mammal_sentence_332

The surface of their wings is equipped with touch-sensitive receptors on small bumps called Merkel cells, also found on human fingertips. Mammal_sentence_333

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. Mammal_sentence_334

Fossorial and subterranean Mammal_section_25

See also: Fossorial and Burrow Mammal_sentence_335

A fossorial (from Latin fossor, meaning "digger") is an animal adapted to digging which lives primarily, but not solely, underground. Mammal_sentence_336

Some examples are badgers, and naked mole-rats. Mammal_sentence_337

Many rodent species are also considered fossorial because they live in burrows for most but not all of the day. Mammal_sentence_338

Species that live exclusively underground are subterranean, and those with limited adaptations to a fossorial lifestyle sub-fossorial. Mammal_sentence_339

Some organisms are fossorial to aid in temperature regulation while others use the underground habitat for protection from predators or for food storage. Mammal_sentence_340

Fossorial mammals have a fusiform body, thickest at the shoulders and tapering off at the tail and nose. Mammal_sentence_341

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. Mammal_sentence_342

External ears flaps are also very small or absent. Mammal_sentence_343

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. Mammal_sentence_344

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. Mammal_sentence_345

Most have large incisors to prevent dirt from flying into their mouth. Mammal_sentence_346

Many fossorial mammals such as shrews, hedgehogs, and moles were classified under the now obsolete order Insectivora. Mammal_sentence_347

Aquatic Mammal_section_26

Main articles: Aquatic locomotion, Marine mammal, and Aquatic mammal Mammal_sentence_348

Fully aquatic mammals, the cetaceans and sirenians, have lost their legs and have a tail fin to propel themselves through the water. Mammal_sentence_349

Flipper movement is continuous. Mammal_sentence_350

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. Mammal_sentence_351

Their skeletal anatomy allows them to be fast swimmers. Mammal_sentence_352

Most species have a dorsal fin to prevent themselves from turning upside-down in the water. Mammal_sentence_353

The flukes of sirenians are raised up and down in long strokes to move the animal forward, and can be twisted to turn. Mammal_sentence_354

The forelimbs are paddle-like flippers which aid in turning and slowing. Mammal_sentence_355

Semi-aquatic mammals, like pinnipeds, have two pairs of flippers on the front and back, the fore-flippers and hind-flippers. Mammal_sentence_356

The elbows and ankles are enclosed within the body. Mammal_sentence_357

Pinnipeds have several adaptions for reducing drag. Mammal_sentence_358

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. Mammal_sentence_359

They also lack arrector pili, so their fur can be streamlined as they swim. Mammal_sentence_360

They rely on their fore-flippers for locomotion in a wing-like manner similar to penguins and sea turtles. Mammal_sentence_361

Fore-flipper movement is not continuous, and the animal glides between each stroke. Mammal_sentence_362

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. Mammal_sentence_363

Other semi-aquatic mammals include beavers, hippopotamuses, otters and platypuses. Mammal_sentence_364

Hippos are very large semi-aquatic mammals, and their barrel-shaped bodies have skeletal structures, adapted to carrying their enormous weight, and their specific gravity allows them to sink and move along the bottom of a river. Mammal_sentence_365

Behavior Mammal_section_27

Communication and vocalization Mammal_section_28

Further information: Animal communication and Animal echolocation Mammal_sentence_366

Many mammals communicate by vocalizing. Mammal_sentence_367

Vocal communication serves many purposes, including in mating rituals, as warning calls, to indicate food sources, and for social purposes. Mammal_sentence_368

Males often call during mating rituals to ward off other males and to attract females, as in the roaring of lions and red deer. Mammal_sentence_369

The songs of the humpback whale may be signals to females; they have different dialects in different regions of the ocean. Mammal_sentence_370

Social vocalizations include the territorial calls of gibbons, and the use of frequency in greater spear-nosed bats to distinguish between groups. Mammal_sentence_371

The vervet monkey gives a distinct alarm call for each of at least four different predators, and the reactions of other monkeys vary according to the call. Mammal_sentence_372

For example, if an alarm call signals a python, the monkeys climb into the trees, whereas the eagle alarm causes monkeys to seek a hiding place on the ground. Mammal_sentence_373

Prairie dogs similarly have complex calls that signal the type, size, and speed of an approaching predator. Mammal_sentence_374

Elephants communicate socially with a variety of sounds including snorting, screaming, trumpeting, roaring and rumbling. Mammal_sentence_375

Some of the rumbling calls are infrasonic, below the hearing range of humans, and can be heard by other elephants up to 6 miles (9.7 km) away at still times near sunrise and sunset. Mammal_sentence_376

Mammals signal by a variety of means. Mammal_sentence_377

Many give visual anti-predator signals, as when deer and gazelle stot, honestly indicating their fit condition and their ability to escape, or when white-tailed deer and other prey mammals flag with conspicuous tail markings when alarmed, informing the predator that it has been detected. Mammal_sentence_378

Many mammals make use of scent-marking, sometimes possibly to help defend territory, but probably with a range of functions both within and between species. Mammal_sentence_379

Microbats and toothed whales including oceanic dolphins vocalize both socially and in echolocation. Mammal_sentence_380

Feeding Mammal_section_29

To maintain a high constant body temperature is energy expensive—mammals therefore need a nutritious and plentiful diet. Mammal_sentence_381

While the earliest mammals were probably predators, different species have since adapted to meet their dietary requirements in a variety of ways. Mammal_sentence_382

Some eat other animals—this is a carnivorous diet (and includes insectivorous diets). Mammal_sentence_383

Other mammals, called herbivores, eat plants, which contain complex carbohydrates such as cellulose. Mammal_sentence_384

An herbivorous diet includes subtypes such as granivory (seed eating), folivory (leaf eating), frugivory (fruit eating), nectarivory (nectar eating), gummivory (gum eating) and mycophagy (fungus eating). Mammal_sentence_385

The digestive tract of an herbivore is host to bacteria that ferment these complex substances, and make them available for digestion, which are either housed in the multichambered stomach or in a large cecum. Mammal_sentence_386

Some mammals are coprophagous, consuming feces to absorb the nutrients not digested when the food was first ingested. Mammal_sentence_387

An omnivore eats both prey and plants. Mammal_sentence_388

Carnivorous mammals have a simple digestive tract because the proteins, lipids and minerals found in meat require little in the way of specialized digestion. Mammal_sentence_389

Exceptions to this include baleen whales who also house gut flora in a multi-chambered stomach, like terrestrial herbivores. Mammal_sentence_390

The size of an animal is also a factor in determining diet type (Allen's rule). Mammal_sentence_391

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. Mammal_sentence_392

Mammals that weigh less than about 18 ounces (510 g; 1.1 lb) are mostly insectivorous because they cannot tolerate the slow, complex digestive process of an herbivore. Mammal_sentence_393

Larger animals, on the other hand, generate more heat and less of this heat is lost. Mammal_sentence_394

They can therefore tolerate either a slower collection process (carnivores that feed on larger vertebrates) or a slower digestive process (herbivores). Mammal_sentence_395

Furthermore, mammals that weigh more than 18 ounces (510 g; 1.1 lb) usually cannot collect enough insects during their waking hours to sustain themselves. Mammal_sentence_396

The only large insectivorous mammals are those that feed on huge colonies of insects (ants or termites). Mammal_sentence_397

Some mammals are omnivores and display varying degrees of carnivory and herbivory, generally leaning in favor of one more than the other. Mammal_sentence_398

Since plants and meat are digested differently, there is a preference for one over the other, as in bears where some species may be mostly carnivorous and others mostly herbivorous. Mammal_sentence_399

They are grouped into three categories: mesocarnivory (50–70% meat), hypercarnivory (70% and greater of meat), and hypocarnivory (50% or less of meat). Mammal_sentence_400

The dentition of hypocarnivores consists of dull, triangular carnassial teeth meant for grinding food. Mammal_sentence_401

Hypercarnivores, however, have conical teeth and sharp carnassials meant for slashing, and in some cases strong jaws for bone-crushing, as in the case of hyenas, allowing them to consume bones; some extinct groups, notably the Machairodontinae, had saber-shaped canines. Mammal_sentence_402

Some physiological carnivores consume plant matter and some physiological herbivores consume meat. Mammal_sentence_403

From a behavioral aspect, this would make them omnivores, but from the physiological standpoint, this may be due to zoopharmacognosy. Mammal_sentence_404

Physiologically, animals must be able to obtain both energy and nutrients from plant and animal materials to be considered omnivorous. Mammal_sentence_405

Thus, such animals are still able to be classified as carnivores and herbivores when they are just obtaining nutrients from materials originating from sources that do not seemingly complement their classification. Mammal_sentence_406

For example, it is well documented that some ungulates such as giraffes, camels, and cattle, will gnaw on bones to consume particular minerals and nutrients. Mammal_sentence_407

Also, cats, which are generally regarded as obligate carnivores, occasionally eat grass to regurgitate indigestible material (such as hairballs), aid with hemoglobin production, and as a laxative. Mammal_sentence_408

Many mammals, in the absence of sufficient food requirements in an environment, suppress their metabolism and conserve energy in a process known as hibernation. Mammal_sentence_409

In the period preceding hibernation, larger mammals, such as bears, become polyphagic to increase fat stores, whereas smaller mammals prefer to collect and stash food. Mammal_sentence_410

The slowing of the metabolism is accompanied by a decreased heart and respiratory rate, as well as a drop in internal temperatures, which can be around ambient temperature in some cases. Mammal_sentence_411

For example, the internal temperatures of hibernating arctic ground squirrels can drop to −2.9 °C (26.8 °F), however the head and neck always stay above 0 °C (32 °F). Mammal_sentence_412

A few mammals in hot environments aestivate in times of drought or extreme heat, for example the fat-tailed dwarf lemur (Cheirogaleus medius). Mammal_sentence_413

Intelligence Mammal_section_30

See also: Animal cognition Mammal_sentence_414

In intelligent mammals, such as primates, the cerebrum is larger relative to the rest of the brain. Mammal_sentence_415

Intelligence itself is not easy to define, but indications of intelligence include the ability to learn, matched with behavioral flexibility. Mammal_sentence_416

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. Mammal_sentence_417

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. Mammal_sentence_418

Tool use by animals may indicate different levels of learning and cognition. Mammal_sentence_419

The sea otter uses rocks as essential and regular parts of its foraging behaviour (smashing abalone from rocks or breaking open shells), with some populations spending 21% of their time making tools. Mammal_sentence_420

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. Mammal_sentence_421

Tools may even be used in solving puzzles in which the animal appears to experience a "Eureka moment". Mammal_sentence_422

Other mammals that do not use tools, such as dogs, can also experience a Eureka moment. Mammal_sentence_423

Brain size was previously considered a major indicator of the intelligence of an animal. Mammal_sentence_424

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. Mammal_sentence_425

Allometric analysis indicates that mammalian brain size scales at approximately the ​⁄3 or ​⁄4 exponent of the body mass. Mammal_sentence_426

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. Mammal_sentence_427

Sperm whales have the largest brain mass of any animal on earth, averaging 8,000 cubic centimetres (490 in) and 7.8 kilograms (17 lb) in mature males. Mammal_sentence_428

Self-awareness appears to be a sign of abstract thinking. Mammal_sentence_429

Self-awareness, although not well-defined, is believed to be a precursor to more advanced processes such as metacognitive reasoning. Mammal_sentence_430

The traditional method for measuring this is the mirror test, which determines if an animal possesses the ability of self-recognition. Mammal_sentence_431

Mammals that have passed the mirror test include Asian elephants (some pass, some do not); chimpanzees; bonobos; orangutans; humans, from 18 months (mirror stage); bottlenose dolphins killer whales; and false killer whales. Mammal_sentence_432

Social structure Mammal_section_31

Main article: Social animal Mammal_sentence_433

Eusociality is the highest level of social organization. Mammal_sentence_434

These societies have an overlap of adult generations, the division of reproductive labor and cooperative caring of young. Mammal_sentence_435

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. Mammal_sentence_436

Presociality is when animals exhibit more than just sexual interactions with members of the same species, but fall short of qualifying as eusocial. Mammal_sentence_437

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. Mammal_sentence_438

Humans and some species of Callitrichidae (marmosets and tamarins) are unique among primates in their degree of cooperative care of young. Mammal_sentence_439

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. Mammal_sentence_440

A fission-fusion society is a society that changes frequently in its size and composition, making up a permanent social group called the "parent group". Mammal_sentence_441

Permanent social networks consist of all individual members of a community and often varies to track changes in their environment. Mammal_sentence_442

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. Mammal_sentence_443

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. Mammal_sentence_444

Many mammals exhibit this, such as primates (for example orangutans and spider monkeys), elephants, spotted hyenas, lions, and dolphins. Mammal_sentence_445

Solitary animals defend a territory and avoid social interactions with the members of its species, except during breeding season. Mammal_sentence_446

This is to avoid resource competition, as two individuals of the same species would occupy the same niche, and to prevent depletion of food. Mammal_sentence_447

A solitary animal, while foraging, can also be less conspicuous to predators or prey. Mammal_sentence_448

In a hierarchy, individuals are either dominant or submissive. Mammal_sentence_449

A despotic hierarchy is where one individual is dominant while the others are submissive, as in wolves and lemurs, and a pecking order is a linear ranking of individuals where there is a top individual and a bottom individual. Mammal_sentence_450

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. Mammal_sentence_451

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. Mammal_sentence_452

Non-resident males can also be accepted in harems, but some species, such as the common vampire bat (Desmodus rotundus), may be more strict. Mammal_sentence_453

Some mammals 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. Mammal_sentence_454

There are three types of polygamy: either one or multiple dominant males have breeding rights (polygyny), multiple males that females mate with (polyandry), or multiple males have exclusive relations with multiple females (polygynandry). Mammal_sentence_455

It is much more common for polygynous mating to happen, which, excluding leks, are estimated to occur in up to 90% of mammals. Mammal_sentence_456

Lek mating occurs when males congregate around females and try to attract them with various courtship displays and vocalizations, as in harbor seals. Mammal_sentence_457

All higher mammals (excluding monotremes) share two major adaptations for care of the young: live birth and lactation. Mammal_sentence_458

These imply a group-wide choice of a degree of parental care. Mammal_sentence_459

They may build nests and dig burrows to raise their young in, or feed and guard them often for a prolonged period of time. Mammal_sentence_460

Many mammals are K-selected, and invest more time and energy into their young than do r-selected animals. Mammal_sentence_461

When two animals mate, they both share an interest in the success of the offspring, though often to different extremes. Mammal_sentence_462

Mammalian females exhibit some degree of maternal aggression, another example of parental care, which may be targeted against other females of the species or the young of other females; however, some mammals may "aunt" the infants of other females, and care for them. Mammal_sentence_463

Mammalian males may play a role in child rearing, as with tenrecs, however this varies species to species, even within the same genus. Mammal_sentence_464

For example, the males of the southern pig-tailed macaque (Macaca nemestrina) do not participate in child care, whereas the males of the Japanese macaque (M. fuscata) do. Mammal_sentence_465

Humans and other mammals Mammal_section_32

Main article: Human uses of mammals Mammal_sentence_466

In human culture Mammal_section_33

Non-human mammals play a wide variety of roles in human culture. Mammal_sentence_467

They are the most popular of pets, with tens of millions of dogs, cats and other animals including rabbits and mice kept by families around the world. Mammal_sentence_468

Mammals such as mammoths, horses and deer are among the earliest subjects of art, being found in Upper Paleolithic cave paintings such as at Lascaux. Mammal_sentence_469

Major artists such as Albrecht Dürer, George Stubbs and Edwin Landseer are known for their portraits of mammals. Mammal_sentence_470

Many species of mammals have been hunted for sport and for food; deer and wild boar are especially popular as game animals. Mammal_sentence_471

Mammals such as horses and dogs are widely raced for sport, often combined with betting on the outcome. Mammal_sentence_472

There is a tension between the role of animals as companions to humans, and their existence as individuals with rights of their own. Mammal_sentence_473

Mammals further play a wide variety of roles in literature, film, mythology, and religion. Mammal_sentence_474

Uses and importance Mammal_section_34

See also: Livestock, Laboratory animal, and Pack animal Mammal_sentence_475

Domestic mammals form a large part of the livestock raised for meat across the world. Mammal_sentence_476

They include (2009) around 1.4 billion cattle, 1 billion sheep, 1 billion domestic pigs, and (1985) over 700 million rabbits. Mammal_sentence_477

Working domestic animals including cattle and horses have been used for work and transport from the origins of agriculture, their numbers declining with the arrival of mechanised transport and agricultural machinery. Mammal_sentence_478

In 2004 they still provided some 80% of the power for the mainly small farms in the third world, and some 20% of the world's transport, again mainly in rural areas. Mammal_sentence_479

In mountainous regions unsuitable for wheeled vehicles, pack animals continue to transport goods. Mammal_sentence_480

Mammal skins provide leather for shoes, clothing and upholstery. Mammal_sentence_481

Wool from mammals including sheep, goats and alpacas has been used for centuries for clothing. Mammal_sentence_482

Mammals serve a major role in science as experimental animals, both in fundamental biological research, such as in genetics, and in the development of new medicines, which must be tested exhaustively to demonstrate their safety. Mammal_sentence_483

Millions of mammals, especially mice and rats, are used in experiments each year. Mammal_sentence_484

A knockout mouse is a genetically modified mouse with an inactivated gene, replaced or disrupted with an artificial piece of DNA. Mammal_sentence_485

They enable the study of sequenced genes whose functions are unknown. Mammal_sentence_486

A small percentage of the mammals are non-human primates, used in research for their similarity to humans. Mammal_sentence_487

Charles Darwin, Jared Diamond and others have noted the importance of domesticated mammals in the Neolithic development of agriculture and of civilization, causing farmers to replace hunter-gatherers around the world. Mammal_sentence_488

This transition from hunting and gathering to herding flocks and growing crops was a major step in human history. Mammal_sentence_489

The new agricultural economies, based on domesticated mammals, caused "radical restructuring of human societies, worldwide alterations in biodiversity, and significant changes in the Earth's landforms and its atmosphere... momentous outcomes". Mammal_sentence_490

Hybrids Mammal_section_35

Main article: Hybrid (biology) Mammal_sentence_491

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. Mammal_sentence_492

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. Mammal_sentence_493

Hybrids between different subspecies within a species (such as between the Bengal tiger and Siberian tiger) are known as intra-specific hybrids. Mammal_sentence_494

Hybrids between different species within the same genus (such as between lions and tigers) are known as interspecific hybrids or crosses. Mammal_sentence_495

Hybrids between different genera (such as between sheep and goats) are known as intergeneric hybrids. Mammal_sentence_496

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. Mammal_sentence_497

Some hybrids have been recognized as species, such as the red wolf (though this is controversial). Mammal_sentence_498

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. Mammal_sentence_499

A breeding-back (intraspecific) hybrid may be very similar to the extinct wildtype in appearance, ecological niche and to some extent genetics, but the initial gene pool of that wild type is lost forever with its extinction. Mammal_sentence_500

As a result, bred-back breeds are at best vague look-alikes of extinct wildtypes, as Heck cattle are of the aurochs. Mammal_sentence_501

Purebred wild species evolved to a specific ecology can be threatened with extinction through the process of genetic pollution, the uncontrolled hybridization, introgression genetic swamping which leads to homogenization or out-competition from the heterosic hybrid species. Mammal_sentence_502

When new populations are imported or selectively bred by people, or when habitat modification brings previously isolated species into contact, extinction in some species, especially rare varieties, is possible. Mammal_sentence_503

Interbreeding can swamp the rarer gene pool and create hybrids, depleting the purebred gene pool. Mammal_sentence_504

For example, the endangered wild water buffalo is most threatened with extinction by genetic pollution from the domestic water buffalo. Mammal_sentence_505

Such extinctions are not always apparent from a morphological standpoint. Mammal_sentence_506

Some degree of gene flow is a normal evolutionary process, nevertheless, hybridization threatens the existence of rare species. Mammal_sentence_507

Threats Mammal_section_36

See also: Holocene extinction Mammal_sentence_508

The loss of species from ecological communities, defaunation, is primarily driven by human activity. Mammal_sentence_509

This has resulted in empty forests, ecological communities depleted of large vertebrates. Mammal_sentence_510

In the Quaternary extinction event, the mass die-off of megafaunal variety coincided with the appearance of humans, suggesting a human influence. Mammal_sentence_511

One hypothesis is that humans hunted large mammals, such as the woolly mammoth, into extinction. Mammal_sentence_512

The 2019 Global Assessment Report on Biodiversity and Ecosystem Services by IPBES states that the total biomass of wild mammals has declined by 82 percent since the beginning of human civilization. Mammal_sentence_513

Wild animals make up just 4% of mammalian biomass on earth, while humans and their domesticated animals make up 96%. Mammal_sentence_514

Various species are predicted to become extinct in the near future, among them the rhinoceros, primates, pangolins, and giraffes. Mammal_sentence_515

According to the WWF's 2020 Living Planet Report, vertebrate wildlife populations have declined by 68% since 1970 as a result of human activities, particularly overconsumption, population growth and intensive farming, which is evidence that humans have triggered a sixth mass extinction event. Mammal_sentence_516

Hunting alone threatens hundreds of mammalian species around the world. Mammal_sentence_517

Scientists claim that the growing demand for meat is contributing to biodiversity loss as this is a significant driver of deforestation and habitat destruction; species-rich habitats, such as significant portions of the Amazon rainforest, are being converted to agricultural land for meat production. Mammal_sentence_518

Another influence is over-hunting and poaching, which can reduce the overall population of game animals, especially those located near villages, as in the case of peccaries. Mammal_sentence_519

The effects of poaching can especially be seen in the ivory trade with African elephants. Mammal_sentence_520

Marine mammals are at risk from entanglement from fishing gear, notably cetaceans, with discard mortalities ranging from 65,000 to 86,000 individuals annually. Mammal_sentence_521

Attention is being given to endangered species globally, notably through the Convention on Biological Diversity, otherwise known as the Rio Accord, which includes 189 signatory countries that are focused on identifying endangered species and habitats. Mammal_sentence_522

Another notable conservation organization is the IUCN, which has a membership of over 1,200 governmental and non-governmental organizations. Mammal_sentence_523

Recent extinctions can be directly attributed to human influences. Mammal_sentence_524

The IUCN characterizes 'recent' extinction as those that have occurred past the cut-off point of 1500, and around 80 mammal species have gone extinct since that time and 2015. Mammal_sentence_525

Some species, such as the Père David's deer are extinct in the wild, and survive solely in captive populations. Mammal_sentence_526

Other species, such as the Florida panther, are ecologically extinct, surviving in such low numbers that they essentially have no impact on the ecosystem. Mammal_sentence_527

Other populations are only locally extinct (extirpated), still existing elsewhere, but reduced in distribution, as with the extinction of gray whales in the Atlantic. Mammal_sentence_528

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