Mammal classification

Mammalia is a class of animal within the Phylum Chordata. Mammal classification has been through several iterations since Carolus Linnaeus initially defined the class. Many earlier ideas have been completely abandoned by modern taxonomists, among these are the idea that bats are related to birds or that humans represent a completely distinct group. Competing ideas about the relationships of mammal orders do persist and are currently in development. Most significantly in recent years, cladistic thinking has led to an effort to ensure that all taxonomic designations represent monophyletic groups. The field has also seen a recent surge in interest and modification due to the results of molecular phylogenetics.

George Gaylord Simpson's classic "Principles of Classification and a Classification of Mammals" (Simpson, 1945) was the original source for the taxonomy listed here. Simpson laid out a systematics of mammal origins and relationships that was universally taught until the end of the 20th century.

Since Simpson's 1945 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 Though field work gradually made Simpson's classification outdated, it remained the closest thing to an official classification of mammals.

Molecular classification of mammals
Molecular studies by molecular systematists, based on DNA analysis, have revealed new relationships among mammal families over the last few years. The most recent classification systems based on molecular studies reveal four groups or lineages of placental mammals which diverged from early common ancestors in the Cretaceous.

The first divergence was that of the Afrotheria 110–100 million years ago (mya). The Afrotheria proceeded to evolve and diversify in the isolation of the African-Arabian continent. The Xenarthra, isolated in South America, diverged from the Boreoeutheria approximately 100–95 mya. The Boreoeutheria split into the Laurasiatheria and Euarchontoglires between 95 and 85 mya; both of these groups evolved on the northern continent of Laurasia.

After tens of millions of years of relative isolation, Africa-Arabia collided with Eurasia, and the formation of the Isthmus of Panama linked South America and North America, facilitating the distribution of mammals seen today. With the exception of bats and murine rodents, no placental land mammals reached Australasia until the first human settlers arrived approximately 50,000 years ago.

It should however be noted that these molecular results are still controversial mainly because they are not reflected by morphological data and thus not accepted by many systematists. It is also important to note that fossil taxa are not and, in most cases cannot, be included. Although there are instances of DNA being recovered from prehistoric mammals such as the ground sloth Mylodon and Neanderthal humans, Homo neanderthalensis, fossils can generally only be incorporated in morphological analyses.

The following taxonomy only includes living placentals (infraclass Eutheria):

Group I: Afrotheria

 * Clade Afroinsectiphilia
 * Order Macroscelidea
 * Family Macroscelididae: elephant shrews (Africa).
 * Order Afrosoricida
 * Family Tenrecidae: tenrecs (Madagascar) and otter-shrews (West and Central Africa).
 * Family Chrysochloridae: golden moles (Africa south of the Sahara).
 * Order Tubulidentata
 * Family Orycteropodidae: aardvark (Africa south of the Sahara).
 * Clade Paenungulata
 * Order Proboscidea
 * Family Elephantidae: elephants (Africa, Southeast Asia).
 * Order Hyracoidea
 * Family Procaviidae: hyraxes, dassies (Africa, Arabia).
 * Order Sirenia
 * Family Dugongidae: dugong (East Africa, Red Sea, North Australia).
 * Family Trichechidae: manatees (tropical Atlantic coasts and adjacent rivers).

Group II: Xenarthra

 * Order Cingulata
 * Family Dasypodidae: armadillos (Neotropical and Nearctic)
 * Order Pilosa
 * Family Myrmecophagidae: anteaters (Neotropical)
 * Family Megalonychidae: two-toed sloths
 * Family Bradypodidae: three-toed sloths

Group III Euarchontoglires

 * Superorder Euarchonta
 * Order Scandentia
 * Family Ptilocercidae
 * Family Tupaiidae: tree shrews (Southeast Asia).
 * Clade Primatomorpha
 * Order Dermoptera
 * Family Cynocephalidae: flying lemurs or colugos (Southeast Asia).
 * Order Primates: lemurs, bushbabies, monkeys, apes (cosmopolitan).
 * Family Cheirogaleidae: dwarf lemurs (Madagascar)
 * Family Lemuridae: lemurs (Madagascar)
 * Family Lepilemuridae: mongoose lemurs (Madagascar)
 * Family Indriidae: indri and sifakas (Madagascar)
 * Family Daubentoniidae: aye-aye (Madagascar area)
 * Family Lorisidae: lorises and potto (Africa and Southeast Asia)
 * Family Galagidae: galagos (Africa)
 * Family Tarsiidae: tarsiers (Southeast Asia)
 * Family Callitrichidae: marmosets and tamarins (South America)
 * Family Cebidae: New World monkeys (South America)
 * Family Cercopithecidae: Old World monkeys (Africa and Eurasia)
 * Family Hylobatidae: gibbons (Southeast Asia)
 * Family Hominidae: great apes (worldwide)
 * Superorder Glires
 * Order Lagomorpha: pikas, rabbits, hares (Eurasia, Africa, Americas).
 * Family Leporidae: rabbits and hares (Eurasia, Africa, Americas)
 * Family Ochotonidae: pikas (Holarctic)
 * Order Rodentia: rodents (cosmopolitan)
 * Family Aplodontiidae: mountain beaver (North America)
 * Family Sciuridae: squirrels, chipmunks, and marmots (cosmopolitan except Australia)
 * Family Gliridae: dormice (Africa, Eurasia)
 * Family Castoridae: beavers (Holarctic)
 * Family Geomyidae: pocket gophers (North America)
 * Family Heteromyidae: kangaroo rats (North America)
 * Family Dipodidae: jerboas and jumping mice (Africa, Eurasia, North America)
 * Family Platacanthomyidae: spiny dormouse (Southeast Asia)
 * Family Spalacidae: zokors, root rats, blind mole rats (Africa, Eurasia)
 * Family Calomyscidae: mouse-like hamsters (Asia)
 * Family Nesomyidae: old endemic African muroids (Africa, Madagascar)
 * Family Cricetidae: hamsters, voles, and New World rats and mice (Holarctic, South America)
 * Family Muridae: Old World rats and mice and gerbils (Africa, Eurasia, Australia)
 * Family Anomaluridae: scaly-tailed flying squirrels (Africa)
 * Family Pedetidae: springhaas (Africa)
 * Family Ctenodactylidae: gundis (Africa, Asia)
 * Family Hystricidae: Old World porcupines (Africa, Asia)
 * Family Bathyergidae: African mole-rats (Africa)
 * Family Petromuridae: rock dassies (Africa)
 * Family Thryonomyidae: cane rats (Africa)
 * Family Erethizontidae: New World porcupines (New World)
 * Family Chinchillidae: chinchillas and viscachas (South America)
 * Family Dinomyidae: pacarana (South America)
 * Family Caviidae: cavies and capybara (South America)
 * Family Dasyproctidae: agoutis and acouchis (South America)
 * Family Agoutidae: paca (South America)
 * Family Ctenomyidae: tuco-tucos (South America)
 * Family Octodontidae: degus (South America)
 * Family Abrocomidae: chinchilla-rats (South America)
 * Family Echimyidae: spiny rats (South America)
 * Family Capromyidae: hutias (South America)
 * Family Myocastoridae: nutrias (South America)

Group IV: Laurasiatheria

 * Order Soricomorpha
 * Family Solenodontidae: solenodons (Cuba, Hispaniola).
 * Family Soricidae: shrews (Eurasia, Africa, North America to northern South America).
 * Family Talpidae: moles, shrew-moles, desmans (Eurasia, North America).
 * Order Erinaceomorpha
 * Family Erinaceidae: hedgehogs, moonrats (Eurasia, Africa).
 * Clade Ferungulata
 * Order Cetartiodactyla: includes former orders Artiodactyla and Cetacea
 * Family Camelidae: camels (South America, Asia)
 * Family Suidae: pigs (Africa, Eurasia)
 * Family Tayassuidae: peccaries (New World)
 * Family Hippopotamidae: hippos (Africa)
 * Family Balaenopteridae: rorquals and grey whales
 * Family Balaenidae: right and bowhead whales
 * Family Physeteridae: sperm whales
 * Family Hyperoodontidae: beaked whales
 * Family Platanistidae: river dolphins
 * Family Delphinidae: dolphins
 * Family Pontoporiidae: La Plata River dolphin
 * Family Lipotidae: baiji
 * Family Iniidae: Amazon River dolphin
 * Family Monodontidae: beluga and narwhal
 * Family Phocoenidae: porpoises
 * Family Tragulidae: mouse-deer (Africa, Asia)
 * Family Antilocapridae: pronghorn (North America)
 * Family Giraffidae: giraffe and okapi (Africa)
 * Family Cervidae: deer (Holarctic, South America)
 * Family Moschidae: musk deer (Asia)
 * Family Bovidae: cattle, antelope, sheep, etc. (Africa, Holarctic)
 * Clade Pegasoferae
 * Order Chiroptera: bats (cosmopolitan)
 * Family Pteropodidae: flying foxes (Africa, Eurasia, Australia)
 * Family Rhinolophidae: Old World horseshoe and leaf-nosed bats (Old World)
 * Family Emballonuridae: sac-winged bats (southern continents)
 * Family Craseonycteridae: Kitti's hog-nosed bat (Thailand)
 * Family Rhinopomatidae: mouse-tailed bats (Africa, Southeast Asia)
 * Family Nycteridae: slit-faced bats (Africa, Southeast Asia)
 * Family Megadermatidae: false vampire bats (Africa, Southeast Asia, Australia)
 * Family Phyllostomidae: leaf-nosed bats (South America)
 * Family Mormoopidae: leaf-chinned bats (South America)
 * Family Noctilionidae: fishing bats (South America)
 * Family Mystacinidae: short-tailed bats (New Zealand)
 * Family Molossidae: free-tailed bats (cosmopolitan)
 * Family Myzopodidae: sucker-footed bats (Madagascar)
 * Family Thyropteridae: sucker-footed bats (South America)
 * Family Furipteridae: smoky bats (South America)
 * Family Natalidae: funnel-eared bats (South America)
 * Family Vespertilionidae: vesper bats (cosmopolitan)
 * Order Perissodactyla: odd-toed ungulates
 * Family Equidae: horses, zebras, donkeys (Africa, West and Central Asia).
 * Family Tapiridae: tapirs (Central and South America, Southeast Asia).
 * Family Rhinocerotidae: rhinoceroses (Africa, Southeast Asia).
 * Clade Ferae
 * Order Pholidota
 * Family Manidae: pangolins, scaly anteaters (Africa, South Asia).
 * Order Carnivora: carnivorans (cosmopolitan)
 * Family Felidae: cats
 * Family Viverridae: civets, Asiatic palm civets
 * Family Herpestidae: mongooses
 * Family Hyaenidae: hyaenas, aardwolf
 * Family Canidae: dogs
 * Family Ursidae: bears
 * Family Otariidae: eared seals
 * Family Odobenidae: walrus
 * Family Phocidae: seals, walrus
 * Family Ailuridae: red panda
 * Family Mephitidae: skunks
 * Family Mustelidae: weasels and relatives
 * Family Procyonidae: ringtails, olingos, kinkajou, raccoons, coatis, red panda

Standardized textbook classification
A somewhat standardized classification system has been adopted by most current mammalogy classroom textbooks. The following taxonomy of extant and recently extinct mammals is taken from Vaughan et al. (2000). This approach emphasizes an initial split between egg-laying prototherians and live-bearing therians. The therians are further divided into the marsupial Metatheria and the "placental" Eutheria. No attempt is made here to further distinguish among the orders within these subclasses and infraclasses. This system also makes no note of the position of entirely fossil groups.

In this and later taxonomies listed here, families are merely listed under the order to which they belong. Please see the pages associated with specific orders to see more detailed relationships among families in that order.

Subclass Prototheria

 * Order Monotremata
 * Family Tachyglossidae (echidnas)
 * Family Ornithorhynchidae (platypuses)

Subclass Theria

 * Infraclass Metatheria (marsupials and their nearest ancestors)
 * Order Didelphimorphia
 * Family Didelphidae (opossums, etc.)
 * Order Paucituberculata
 * Family Caenolestidae (shrew opossums)
 * Order Microbiotheria
 * Family Microbiotheriidae (monito del montes)
 * Order Dasyuromorphia (most carnivorous marsupials)
 * Family Thylacinidae (Tasmanian tigers)
 * Family Myrmecobiidae (numbats)
 * Family Dasyuridae (Tasmanian devils, quolls, dunnarts, planigale, etc.)
 * Order Peramelemorphia (bandicoots, bilbies, etc.)
 * Family Peramelidae
 * Family Peroryctidae
 * Order Notoryctemorphia (marsupial moles)
 * Family Notoryctidae
 * Order Diprotodontia
 * Family Phascolarctidae (koalas)
 * Family Vombatidae (wombats)
 * Family Phalangeridae (brushtail possums and cuscuses)
 * Family Potoroidae (bettongs, potaroos and rat kangaroos)
 * Family Macropodidae (kangaroos, wallabies, etc.)
 * Family Burramyidae (pygmy possums)
 * Family Pseudocheiridae (ringtailed possums, etc.)
 * Family Petauridae (Striped Possum, Leadbeater's Possum, Yellow-bellied Glider, Sugar Glider, Mahogany Glider and Squirrel Glider)
 * Family Tarsipedidae (honey possum)
 * Family Acrobatidae (Feathertail Glider and Feather-tailed Possum)
 * Infraclass Eutheria
 * Order Xenarthra
 * Family Bradypodidae
 * Family Megalonychidae
 * Family Dasypodidae
 * Family Myrmecophagidae
 * Order Insectivora
 * Family Solenodontidae
 * Family Nesophontidae
 * Family Tenrecidae
 * Family Chrysochloridae
 * Family Erinaceidae
 * Family Soricidae
 * Family Talpidae
 * Order Scandentia
 * Family Tupaiidae
 * Order Dermoptera
 * Family Cynocephalidae
 * Order Chiroptera
 * Family Pteropodidae
 * Family Emballonuridae
 * Family Craseonycteridae
 * Family Rhinopomatidae
 * Family Nycteridae
 * Family Megadermatidae
 * Family Rhinolophidae
 * Family Phyllostomidae
 * Family Mormoopidae
 * Family Noctilionidae
 * Family Mystacinidae
 * Family Molossidae
 * Family Myzopodidae
 * Family Thyropteridae
 * Family Furipteridae
 * Family Natalidae
 * Family Vespertilionidae
 * Order Primates
 * Family Daubentoniidae
 * Family Lemuridae
 * Family Lepilemuridae
 * Family Galagidae
 * Family Lorisidae
 * Family Cheirogaleidae
 * Family Indriidae
 * Family Tarsiidae
 * Family Cercopithecidae
 * Family Hominidae
 * Family Hylobatidae
 * Family Callitrichidae
 * Family Cebidae
 * Order Carnivora
 * Family Felidae
 * Family Viverridae
 * Family Herpestidae
 * Family Hyaenidae
 * Family Canidae
 * Family Ursidae
 * Family Otariidae
 * Family Phocidae
 * Family Odobenidae
 * Family Mustelidae
 * Family Procyonidae
 * Order Cetacea
 * Family Balaenopteridae
 * Family Eschrichtiidae
 * Family Balaenidae
 * Family Neobalaenidae
 * Family Physeteridae
 * Family Ziphiidae
 * Family Platanistidae
 * Family Delphinidae
 * Family Monodontidae
 * Family Phocoenidae
 * Order Sirenia
 * Family Dugongidae
 * Family Trichechidae
 * Order Proboscidea
 * Family Elephantidae
 * Order Perissodactyla
 * Family Equidae
 * Family Tapiridae
 * Family Rhinocerotidae
 * Order Hyracoidea
 * Family Procaviidae
 * Order Tubulidentata
 * Family Orycteropodidae
 * Order Artiodactyla
 * Family Suidae
 * Family Tayassuidae
 * Family Hippopotamidae
 * Family Camelidae
 * Family Tragulidae
 * Family Giraffidae
 * Family Moschidae
 * Family Cervidae
 * Family Antilocapridae
 * Family Bovidae
 * Order Pholidota
 * Family Manidae
 * Order Rodentia
 * Family Aplodontiidae
 * Family Sciuridae
 * Family Castoridae
 * Family Geomyidae
 * Family Heteromyidae
 * Family Dipodidae
 * Family Muridae
 * Family Anomaluridae
 * Family Pedetidae
 * Family Ctenodactylidae
 * Family Myoxidae
 * Family Bathyergidae
 * Family Hystricidae
 * Family Petromuridae
 * Family Thryonomyidae
 * Family Erethizontidae
 * Family Chinchillidae
 * Family Dinomyidae
 * Family Caviidae
 * Family Hydrochaeridae
 * Family Dasyproctidae
 * Family Agoutidae
 * Family Ctenomyidae
 * Family Octodontidae
 * Family Abrocomidae
 * Family Echimyidae
 * Family Capromyidae
 * Family Heptaxodontidae
 * Family Myocastoridae
 * Order Lagomorpha
 * Family Ochotonidae
 * Family Leporidae
 * Order Macroscelidea
 * Family Macroscelididae

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

McKenna and Bell, Classification of Mammals: Above the species level, (McKenna & Bell, 1997) is the most comprehensive work to date on the systematics, relationships, and occurrences of all mammal taxa, living and extinct, down through the rank of genus. The new McKenna/Bell classification was quickly accepted by paleontologists. The authors work 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.

The McKenna/Bell hierarchical listing of all of the terms used for mammal groups above the species includes extinct mammals as well as modern groups, and introduces some fine distinctions such as legions and sublegions (ranks which fall between classes and orders) that are likely to be glossed over by the layman.

The published re-classification forms both a comprehensive and authoritative record of approved names and classifications and a list of invalid names.

Click on the highlighted link for a table comparing the traditional and the new McKenna/Bell classifications of mammals

Extinct groups are represented by †.

Subclass Prototheria
(monotremes)
 * Order Platypoda: platypuses
 * Family Ornithorhynchidae: platypuses
 * Order Tachyglossa: echidnas (spiny anteaters)
 * Family Tachyglossidae: echidnas

Subclass Theriiformes

 * Infraclass †Allotheria
 * Order †Multituberculata: multituberculates
 * Family †Plagiaulacidae
 * Family †Bolodontidae
 * Family †Hahnodontidae
 * Family †Albionbaataridae
 * Family †Arginbaataridae
 * Family †Kogaionidae
 * Family †Sloanbaataridae
 * Family †Cimolodontidae
 * Family †Ptilodontidae
 * Family †Cimolomyidae
 * Family †Eucosmodontidae
 * Family †Taeniolabididae
 * Family †Ferugliotheriidae
 * Family †Sudamericidae
 * Infraclass †Triconodonta
 * Family †Austrotriconodontidae
 * Family †Amphilestidae
 * Family †Triconodontidae
 * Infraclass Holotheria
 * Family †Chronoperatidae
 * Superlegion †Kuehneotheria
 * Family †Kuehneotheriidae
 * Family †Woutersiidae
 * Superlegion Trechnotheria
 * Legion †Symmetrodonta
 * Family †Shuotheriidae
 * Order †Amphidontoidea
 * Family †Amphidontidae
 * Order †Spalacotherioidea
 * Family †Tinodontidae
 * Family †Spalacotheriidae
 * Family †Barbereniidae
 * Legion Cladotheria
 * Sublegion †Dryolestoidea
 * Order †Dryolestida
 * Family †Dryolestidae
 * Family †Paurodontidae
 * Family †Donodontidae
 * Family †Mesungulatidae
 * Family †Reigitheriidae
 * Family †Brandoniidae
 * Order †Amphitheriida
 * Family †Amphitheriidae
 * Sublegion Zatheria
 * Family †Arguitheriidae
 * Family †Arguimuridae
 * Family †Vincelestidae
 * Infralegion †Peramura
 * Family †Peramuridae
 * Infralegion Tribosphenida
 * Family †Necrolestidae
 * Supercohort †Aegialodontia
 * Family †Aegialodontidae
 * Supercohort Theria: therian mammals
 * Family †Pappotheriidae
 * Family †Holoclemensiidae
 * Family †Kermackiidae
 * Family †Endotheriidae
 * Family †Picopsidae
 * Family †Potamotelsidae
 * Family †Plicatodontidae
 * Order †Deltatheroida
 * Family †Deltatheridiidae
 * Family †Deltatheroididae
 * Order †Asiadelphia
 * Family †Asiatheriidae
 * Cohort Marsupialia: marsupials
 * Family †Yingabalanaridae
 * Family †Stagodontidae
 * Family †Pediomyidae
 * Magnorder Australidelphia
 * Superorder Microbiotheria
 * Family Microbiotheriidae: monito del monte
 * Superorder Eometatheria
 * Order †Yalkaparidontia
 * Family †Yalkaparidontidae
 * Order Notoryctemorphia: marsupial moles
 * Family Notoryctidae: marsupial moles
 * Grandorder Dasyuromorphia: marsupial carnivores
 * Family †Thylacinidae: recently extinct Tasmanian tiger and relatives
 * Family Dasyuridae: Tasmanian devil, quolls, etc.
 * Family Myrmecobiidae: numbat
 * Grandorder Syndactyli: syndactylous marsupials
 * Order Peramelia: bandicoots
 * Family Peramelidae
 * Family Peroryctidae
 * Order Diprotodontia
 * Family †Palorchestidae
 * Family †Wynardiidae
 * Family †Thylacoleonidae
 * Family Tarsipedidae: honey possum
 * Family †Ilariidae
 * Family †Diprotodontidae
 * Family Vombatidae: wombats
 * Family Phalangeridae: phalangers
 * Family Burramyidae: pygmy possums
 * Family Macropodidae: rat kangaroos, kangaroos and wallabies
 * Family Petauridae: gliders
 * Family †Ektopodontidae
 * Family Phascolarctidae: koala
 * Family †Pilkipildridae
 * Family †Miralinidae
 * Family Acrobatidae: feather-tail glider, pen-tailed phalanger
 * Magnorder Ameridelphia
 * Order Didelphimorphia: opossums
 * Family Didelphidae: opossums
 * Family †Sparassocynidae
 * Order Paucituberculata
 * Family †Sternbergiidae
 * Family Caenolestidae: rat or shrew opossums
 * Family †Paleothentidae
 * Family †Abderitidae
 * Family †Sillustaniidae
 * Family †Polydolopidae
 * Family †Prepidolopidae
 * Family †Bonapartheriidae
 * Family †Argyrolagidae
 * Family †Patagoniidae
 * Family †Groeberiidae
 * Family †Glasbiidae
 * Family †Caroloameghiniidae
 * Order †Sparassodonta
 * Family †Mayulestidae
 * Family †Hondadelphidae
 * Family †Borhyaenidae
 * Cohort Placentalia: placentals
 * Order †Bibymalagasia
 * Magnorder Xenarthra: edentates
 * Order Cingulata: armadillos and relatives
 * Family Dasypodidae: armadillos
 * Family †Peltephilidae
 * Family †Pampatheriidae
 * Family †Palaeopeltidae
 * Family †Glyptodontidae: glyptodonts
 * Order Pilosa: anteaters, sloths, and relatives
 * Family †Entelopidae
 * Family Myrmecophagidae: giant anteaters and relatives
 * Family Cyclopedidae: pygmy anteater
 * Family †Rathymotheriidae
 * Family †Scelidotheriidae
 * Family †Mylodontidae
 * Family †Megatheriidae: ground sloths
 * Family Megalonychidae: two-toed sloths
 * Family Bradypodidae: three-toed sloths
 * Magnorder Epitheria: epitheres
 * Superorder †Leptictida
 * Family †Gypsonictopidae
 * Family †Kulbeckiidae
 * Family †Didymoconidae
 * Family †Leptictidae
 * Superorder Preptotheria
 * Grandorder Anagalida
 * Family †Zambdalestidae
 * Family †Anagalidae
 * Family †Pseudictopidae
 * Mirorder Macroscelidea: elephant shrews
 * Family Macroscelididae: elephant shrews
 * Mirorder Duplicidentata
 * Order †Mimotonida
 * Family †Mimotonidae
 * Order Lagomorpha
 * Family Ochotonidae: pikas
 * Family Leporidae: rabbits
 * Mirorder Simplicidentata
 * Order †Mixodontia
 * Family †Eurymylidae
 * Order Rodentia: rodents
 * Family †Alagomyidae
 * Family †Laredomyidae
 * Family †Ischyromyidae
 * Family †Allomyidae
 * Family Aplodontiidae: mountain beaver
 * Family †Mylagaulidae
 * Family †Theridomyidae
 * Family †Reithroparamyidae
 * Family Sciuridae: squirrels
 * Family †Eutypomyidae
 * Family Castoridae: beavers
 * Family †Rhizospalacidae
 * Family †Protoptychidae
 * Family †Armintomyidae
 * Family Dipodidae: jumping mice, jerboas
 * Family †Simimyidae
 * Family Muridae: rats, mice, and relatives
 * Family Myoxidae: dormice
 * Family †Eomyidae
 * Family †Florentiamyidae
 * Family Geomyidae: pocket gophers, pocket mice, and kangaroo rats
 * Family Pedetidae: springhaas
 * Family †Parapedetidae
 * Family †Zegdoumyidae
 * Family Anomaluridae: scaly-tailed squirrels
 * Family †Ivanantoniidae
 * Family †Sciuravidae
 * Family †Chapattimyidae
 * Family †Cylindrodontidae
 * Family Ctenodactylidae: gundis
 * Family †Tsaganomyidae
 * Family Hystricidae: Old World porcupines
 * Family Erethizontidae: New World porcupines
 * Family †Myophiomyidae
 * Family †Diamantomyidae
 * Family †Phiomyidae
 * Family †Kenyamyidae
 * Family Petromuridae: rock rats
 * Family Thryonomyidae: cane rats
 * Family Bathyergidae: mole-rats
 * Family †Bathyergoididae
 * Family Agoutidae: agoutis and pacas
 * Family †Eocardiidae
 * Family Dinomyidae: pacarana
 * Family Caviidae: cavies
 * Family Hydrochoeridae: capybara
 * Family Octodontidae: degus, tuco-tucos
 * Family Echimyidae: spiny rats, nutria
 * Family Capromyidae: hutias
 * Family †Heptaxodontidae
 * Family Chinchillidae: chinchillas, viscachas
 * Family †Neoepiblemidae
 * Family Abrocomidae: rat chinchillas
 * Grandorder Ferae
 * Order Cimolesta - pangolins and relatives
 * Family †Palaeoryctidae
 * Family †Cimolestidae
 * Family †Apatemyidae
 * Family †Stylinodontidae
 * Family †Tillotheriidae
 * Family †Wangliidae
 * Family †Harpyodidae
 * Family †Bemalambdidae
 * Family †Pastoralodontidae
 * Family †Titanoideidae
 * Family †Pantolambdidae
 * Family †Barylambdidae
 * Family †Cyriacotheriidae
 * Family †Pantolambdodontidae
 * Family †Coryphodontidae
 * Family †Pantolestidae
 * Family †Paroxyclaenidae
 * Family †Ptolemaiidae
 * Family †Epoicotheriidae
 * Family †Metacheiromyidae
 * Family Manidae: pangolins
 * Family †Ernanodontidae
 * Order †Creodonta: creodonts
 * Family †Hyaenodontidae
 * Family †Oxyaenidae
 * Order Carnivora
 * Family †Viverravidae
 * Family †Nimravidae
 * Family Felidae: cats
 * Family Viverridae: civets, Asiatic palm civets
 * Family Herpestidae: mongooses
 * Family Hyaenidae: hyaenas, aardwolf
 * Family Nandiniidae: African palm civets
 * Family †Miacidae
 * Family Canidae: dogs
 * Family †Amphicyonidae
 * Family Ursidae: bears
 * Family †Hemicyonidae
 * Family Otariidae: eared seals
 * Family Phocidae: seals, walrus
 * Family Mustelidae: weasels, skunks, and relatives
 * Family Procyonidae: ringtails, olingos, kinkajou, raccoons, coatis, red panda
 * Grandorder Lipotyphla
 * Family †Adapisoriculidae
 * Order Chrysochloridea
 * Family Chrysochloridae: golden moles
 * Order Erinaceomorpha
 * Family †Sespedectidae
 * Family †Amphilemuridae
 * Family †Adapisoricidae
 * Family †Creotarsidae
 * Family Erinaceidae: hedgehogs and relatives
 * Family †Proscalopidae
 * Family Talpidae: moles
 * Family †Dimylidae
 * Order Soricomorpha
 * Family †Otlestidae
 * Family †Geolabididae
 * Family †Nesophontidae: recently extinct west Indian shrews
 * Family †Micropternodontidae
 * Family †Apternodontidae
 * Family Solenodontidae: solenodons
 * Family †Plesiosoricidae
 * Family †Nyctitheriidae
 * Family Soricidae: shrews
 * Family Tenrecidae: tenrecs
 * Grandorder Archonta
 * Order Chiroptera: bats
 * Family Pteropodidae: flying foxes
 * Family †Archaeonycteridae
 * Family †Paleochiropterygidae
 * Family †Hassianycterididae
 * Family Emballonuridae: sac-winged bats
 * Family Rhinopomatidae: mouse-tailed bats
 * Family Craseonycteridae: bumblebee bats
 * Family Megadermatidae: false vampire bats
 * Family Nycteridae: hispid bats
 * Family Rhinolophidae: horseshoe and Old World leaf-nosed bats
 * Family Mystacinidae: New Zealand short-tailed bats
 * Family Noctilionidae: fishing bats
 * Family Mormoopidae: spectacled bats
 * Family Phyllostomidae: New World leaf-nosed and vampire bats
 * Family †Philisidae
 * Family Molossidae: free-tailed bats
 * Family Natalidae: funnel-eared bats
 * Family Furipteridae: smoky bats
 * Family Thyropteridae: New World sucker-footed bats
 * Family Myzopodidae: Old World sucker-footed bats
 * Family Vespertilionidae: common bats
 * Order Primates: primates
 * Family †Purgatoriidae
 * Family †Microsyopidae
 * Family †Micromomyidae
 * Family †Picromomyidae
 * Family †Plesiadapidae
 * Family †Palaechthonidae
 * Family †Picrodontidae
 * Family †Paramomyidae
 * Family †Plagiomenidae
 * Family †Mixodectidae
 * Family Galeopithecidae: colugos
 * Family †Plesiopithecidae
 * Family Daubentoniidae: aye-aye
 * Family †Adapidae
 * Family Lemuridae: lemurs
 * Family Lorisidae: lorises and galagos
 * Family Cheirogaleidae: dwarf lemurs
 * Family †Archaeolemuridae
 * Family †Palaeopropithecidae
 * Family Indriidae: indris and sifakas
 * Family †Carpolestidae
 * Family †Omomyidae
 * Family †Microchoeridae
 * Family †Afrotarsiidae
 * Family Tarsiidae: tarsiers
 * Family †Eosimiidae
 * Family †Parapithecidae
 * Family †Pliopithecidae
 * Family Cercopithecidae: Old World monkeys including colobuses
 * Family Hominidae: humans, greater apes, lesser apes
 * Family Callitrichidae: marmosets
 * Family Atelidae: New World monkeys
 * Order Scandentia
 * Family Tupaiidae: tree shrews
 * Grandorder Ungulata: ungulates
 * Order Tubulidentata
 * Family Orycteropodidae: aardvark
 * Order †Dinocerata
 * Family †Uintatheriidae
 * Mirorder Eparctocyona
 * Order †Procreodi
 * Family †Oxyclaenidae
 * Family †Arctocyonidae
 * Order †Condylarthra
 * Family †Hyopsodontidae
 * Family †Mioclaenidae
 * Family †Phenacodontidae
 * Family †Periptychidae
 * Family †Peligrotheriidae
 * Family †Didolodontidae
 * Order †Arctostylopida
 * Family †Arctostylopidae
 * Order Cete: whales and relatives
 * Family †Triisodontidae
 * Family †Mesonychidae: mesonychids
 * Family †Hapalodectidae
 * Family †Basilosauridae
 * Family †Protocetidae
 * Family †Remingtonocetidae
 * Family †Agorophiidae
 * Family †Squalodontidae
 * Family †Rhabdosteidae
 * Family †Aetiocetidae
 * Family †Mammalodontidae
 * Family †Cetotheriidae
 * Family Balaenopteridae: rorquals and grey whales
 * Family Balaenidae: right and bowhead whales
 * Family Physeteridae: sperm whales
 * Family Hyperoodontidae: beaked whales
 * Family Platanistidae: river dolphins
 * Family Delphinidae: dolphins
 * Family Pontoporiidae: La Plata River dolphin
 * Family Lipotidae: baiiji
 * Family Iniidae: Amazon River dolphin
 * Family †Kentridontidae
 * Family Monodontidae: beluga and narwhal
 * Family †Odobenocetopsidae
 * Family †Dalpiazinidae
 * Family †Acrodelphinidae
 * Family Phocoenidae: porpoises
 * Family †Albireonidae
 * Family †Hemisyntrachelidae
 * Order Artiodactyla: even-toed ungulates
 * Family †Raoellidae
 * Family †Choeropotamidae
 * Family Suidae: pigs
 * Family Tayassuidae: peccaries
 * Family †Santheriidae
 * Family Hippopotamidae: hippos
 * Family †Dichobunidae
 * Family †Cebochoeridae
 * Family †Mixtotheriidae
 * Family †Helohyidae
 * Family †Haplobunodontidae
 * Family †Anthracotheriidae
 * Family †Dacrytheriidae
 * Family †Anoplotheriidae
 * Family †Cainotheriidae
 * Family †Agriochoeridae
 * Family †Oreodontidae
 * Family †Entelodontidae
 * Family †Xiphodontidae
 * Family Camelidae: camels and llamas
 * Family †Oromerycidae
 * Family †Protoceratidae
 * Family †Amphimerycidae
 * Family †Hypertragulidae
 * Family Tragulidae: mouse deer
 * Family †Leptomerycidae
 * Family †Bachitheriidae
 * Family †Lophiomerycidae
 * Family †Gelocidae
 * Family Moschidae: musk deer
 * Family Antilocapridae: pronghorn
 * Family †Palaeomerycidae
 * Family †Hoplitomerycidae
 * Family Cervidae: deer
 * Family †Climacoceratidae
 * Family Giraffidae: giraffe and okapi
 * Family Bovidae: cattle, antelope, and relatives
 * Mirorder †Meridiungulata
 * Family †Perutheriidae
 * Family †Amilnedwardsiidae
 * Order †Litopterna
 * Family †Protolipternidae
 * Family †Macraucheniidae
 * Family †Notonychopidae
 * Family †Adianthidae
 * Family †Proterotheriidae
 * Order †Notoungulata: notoungulates
 * Family †Henricosborniidae
 * Family †Notostylopidae
 * Family †Isotemnidae
 * Family †Leontiniidae
 * Family †Notohippidae
 * Family †Toxodontidae
 * Family †Homalodotheriidae
 * Family †Archaeopithecidae
 * Family †Oldfieldthomasiidae
 * Family †Interatheriidae
 * Family †Campanorcidae
 * Family †Mesotheriidae
 * Family †Archaeohyracidae
 * Family †Hegetotheriidae
 * Order †Astrapotheria
 * Family †Eoastrapostylopidae
 * Family †Trigonostylopidae
 * Family †Astrapotheriidae
 * Order †Xenungulata
 * Family †Carodniidae
 * Order †Pyrotheria
 * Family †Pyrotheriidae
 * Mirorder Altungulata
 * Order Perissodactyla: odd-toed ungulates
 * Family Equidae: horses
 * Family †Palaeotheriidae
 * Family †Brontotheriidae
 * Family †Anchilophidae
 * Family †Eomoropidae
 * Family †Chalicotheriidae
 * Family †Hyracodontidae
 * Family Rhinocerotidae: rhinoceroses
 * Family †Helaletidae
 * Family †Isectolophidae
 * Family †Lophiodontidae
 * Family †Deperetellidae
 * Family †Lophialetidae
 * Family Tapiridae: tapirs
 * Order Uranotheria: elephants, manatees, hyraxes, and relatives
 * Family †Pliohyracidae
 * Family Procaviidae: hyraxes
 * Family †Phenacolophidae
 * Family †Arsinoitheriidae
 * Family †Prorastomidae
 * Family Dugongidae: dugongs
 * Family Trichechidae: manatees
 * Family †Desmostylidae
 * Family †Anthracobunidae
 * Family †Moeritheriidae
 * Family †Numidotheriidae
 * Family †Barytheriidae
 * Family †Deinotheriidae
 * Family †Palaeomastodontidae
 * Family †Phiomiidae
 * Family †Hemimastodontidae
 * Family †Mammutidae: mastodons and relatives
 * Family †Gomphotheriidae: gomphotheres
 * Family Elephantidae: modern elephants

Luo, Kielan-Jaworowska, and Cifelli classification
Several important fossil mammal discoveries have been made that have led researchers to question many of the relationships proposed by McKenna and Bell (1997). Additionally, researchers are subjecting taxonomic hypotheses to more rigorous cladistic analyses of early mammal fossils. Luo et al. (2002) summarized existing ideas and proposed new ideas of relationships among mammals at the most basal level. They argued that the term mammal should be defined based on characters (especially the dentary-squamosal jaw articulation) instead of a crown-based definition (the group that contains most recent common ancestor of monotremes and therians and all of its descendants). Their definition of Mammalia is roughly equal to the Mammaliaformes as defined by McKenna and Bell (1997) and other authors. They also define their taxonomic levels as clades and do not apply Linnean hierarchies.

Mammalia
 * †Sinoconodon - earliest and most basal of mammals
 * Unnamed clade 1 - a clade that contains all other mammals. These are characterized by determinant growth and occlusal features of the cheek teeth.
 * †Morganucodontidae - morganucodontids, including †Morganucodon, †Megazostrodon, and others
 * †Docodonta - docodonts, including †Haldanodon and †Castorocauda (Ji et al., 2006)
 * Unnamed clade 2 - a clade containing all living mammals and some fossil relatives. It is characterized by the loss of a postdentary trough and a widened braincase.
 * †Hadrocodium
 * †Kuenotherium
 * Crown-group Mammalia - the group that contains most recent common ancestor of monotremes and therians and all of its descendants. This group is defined by additional characters relating the occlusion of molars and the presence of a well-developed masseteric fossa.
 * Australosphenida - a clade that contains monotremes and their fossil relatives. These fossils include †Ambondro, †Asfaltomylos, †Ausktribosphenos, and †Bishops.  If correct, this clade represents an independent evolution of the tribosphenic molar in southern continents.
 * Trechnotheria - Therians, spalacotheriids and their relatives. They are characterized by features of the scapula, tibia, and humerus.
 * †Spalacotheriidae - including Akidolestes, Zhangheotherium, and Maotherium.
 * Cladotheria - Therians, dryolestids, and their relatives. They are characterized by features of the tribosphenic molar and the angular process of the dentary.
 * †Dryolestidae
 * †Amphitherium - incertae sedis (it may be a prototribosphenidan)
 * Prototribosphenida - Therians and fossil relatives including †Vincelestes. Characterized by features of the cochlea including coiling.
 * †Vincelestes
 * Zatheria - Therians and fossil relatives including the "peramurids". Characterized by the presence of wear in the talonid of the lower molars.
 * †"Peramuridae" - †Peramus and relatives. Known only from preserved mandibles and distinctly zatherian molars.
 * Boreosphenida - Therians and fossil relatives including †Kielantherium. They are characterized by molar features.
 * †Kielantherium
 * †Deltatheroida including †Deltatheridium - incertae sedis (it may represent a metatherian)
 * Crown-group Theria - the group that contains most recent common ancestor of marsupials and placentals and all of its descendants. Characterized by a host of molar features, aspects of the alispenoid, and aspects of the astragalus region.
 * †Eutriconodonta - incertae sedis. Triconodonts appear to be a member of the crown-Mammalia clade, but their relationships within it are unknown.  It is also not certain that they represent a monophyletic group.  Examples include Repenomamus.
 * †Multituberculata - incertae sedis. Luo e al. (2002) argue that multituberculates cannot be confidently placed in a particular clade of mammals.  They suggest that they represent either basal mammals or are sister to the Trechnotheria.

Classification system used in related articles
In light of all the options available, the following classification system has been adopted for use in related articles.

Subclass/Order Monotremata

 * Order Monotremata
 * Family Tachyglossidae: echidnas
 * Family Ornithorhynchidae: platypus
 * Family Kollikodontidae: ancient, extinct monotreme somewhat similar to platypus

Subclass Marsupialia

 * Order Didelphimorphia
 * Family Didelphidae: opossums
 * Order Paucituberculata
 * Family Caenolestidae: shrew or rat opossums
 * Order Microbiotheria
 * Family Microbiotheriidae: Monito del Monte
 * Order Dasyuromorphia
 * Family Thylacinidae: Thylacine
 * Family Dasyuridae: marsupial carnivores
 * Family Myrmecobiidae: Numbat
 * Order Notoryctemorphia
 * Family Notoryctidae: marsupial moles
 * Order Peramelemorphia
 * Family Peramelidae: bandicoots and bilbies
 * Family Peroryctidae: rainforest bandicoots
 * Order Diprotodontia
 * Family Phascolarctidae: Koala
 * Family Vombatidae: wombats
 * Family Phalangeridae: cuscuses, brushtail possums
 * Family Burramyidae: pygmy possums
 * Family Tarsipedidae: Honey Possum
 * Family Petauridae: striped possums, wrist-ringed gliders
 * Family Pseudocheiridae: ringtailed possums and allies
 * Family Potoroidae: potoroos, bettongs
 * Family Acrobatidae: Feathertail Glider
 * Family Hypsiprymnodontidae: Musky Rat Kangaroo
 * Family Macropodidae: kangaroos, wallabies, and allies

Subclass Placentalia

 * Order Xenarthra
 * Family Bradypodidae: three-toed sloths
 * Family Megalonychidae: two-toed sloths
 * Family Cyclopedidae: silky anteaters
 * Family Dasypodidae: armadillos
 * Family Myrmecophagidae: true anteaters
 * Superorder Glires
 * Order Rodentia
 * Suborder Sciurognathi
 * Family Aplodontiidae: Mountain Beaver
 * Family Sciuridae: squirrels, marmots
 * Family Castoridae: beavers
 * Family Geomyidae: pocket gophers
 * Family Heteromyidae: pocket mice, kangaroo rats
 * Family Dipodidae: jerboas, birch mice, jumping mice
 * Family Muridae: rats and mice
 * Family Anomaluridae: scaly-tailed squirrels
 * Family Pedetidae: Springhaas
 * Family Ctenodactylidae: gundis
 * Family Gliridae: dormice
 * Suborder Hystricognathi
 * Family Diatomyidae: Laotian rock rat
 * Family Bathyergidae: mole rats
 * Family Hystricidae: Old World porcupines
 * Family Petromuridae: Dassie Rat
 * Family Thryonomyidae: cane rats
 * Family Erethizontidae: New World porcupines
 * Family Chinchillidae: chinchillas, viscachias
 * Family Dinomyidae: Paracana
 * Family Caviidae: cavies, guinea pigs, Patagonian Hare
 * Family Hydrochoeridae: Capybara
 * Family Dasyproctidae: agoutis, acouchis
 * Family Agoutidae: pacas
 * Family Ctenomyidae: tuco-tucos
 * Family Octodontidae: viscacha rats, coruro
 * Family Abrocomidae: chinchilla rats
 * Family Echimyidae: spiny rats
 * Family Capromyidae: hutias
 * Family Myocastoridae: Nutria
 * Order Lagomorpha
 * Family Ochotonidae: pikas
 * Family Leporidae: rabbits, hares
 * Superorder Euarchonta
 * Order Primates
 * Suborder Strepsirrhini
 * Family Cheirogaleidae: dwarf and mouse lemurs
 * Family Lemuridae: lemurs
 * Family Lepilemuridae: sportive lemurs
 * Family Indriidae: indrid lemurs, sifakas
 * Family Daubentoniidae: Aye-aye
 * Family Lorisidae: lorises, Potto
 * Family Galagidae: galagos
 * Suborder Haplorrhini
 * Family Tarsiidae: tarsiers
 * Family Cebidae: marmosets, tamarins, capuchins and squirrel monkeys
 * Family Aotidae: night or owl monkeys (douroucoulis)
 * Family Pitheciidae: titis, sakis and uakaris
 * Family Atelidae: howler, spider and woolly monkeys
 * Family Cercopithecidae: Old World monkeys
 * Family Hylobatidae: gibbons, siamangs
 * Family Hominidae: Gorilla, chimpanzees, Orangutan, Human
 * Order Scandentia: tree shrews
 * Family Tupaiidae
 * Family Ptilocercidae
 * Order Dermoptera
 * Family Cynocephalidae: colugos
 * Order Insectivora
 * Family Solenodontidae: solenodons
 * Family Nesophontidae: nesophontids
 * Family Erinaceidae: hedgehogs, gymnures
 * Family Soricidae: shrews
 * Family Talpidae: moles and desmans
 * Order Chiroptera
 * Suborder Macrochiroptera
 * Family Pteropodidae: Old World fruit bats
 * Suborder Microchiroptera
 * Family Rhinopomatidae: mouse-tailed bats
 * Family Craseonycteridae: Kitti's Hog-nosed Bat
 * Family Emballonuridae: sac-winged or sheath-tailed bats
 * Family Nycteridae: slit-faced bats
 * Family Megadermatidae: false vampire bats
 * Family Rhinolophidae: horseshoe bats
 * Family Noctilionidae: fishing bats
 * Family Mormoopidae: leaf-chinned bats
 * Family Phyllostomidae: New World leaf-nosed bats
 * Family Natalidae: funnel-eared bats
 * Family Furipteridae: smoky bats
 * Family Thyropteridae: disk-winged bats
 * Family Myzopodidae: Sucker-footed Bat
 * Family Vespertilionidae: common bats
 * Family Mystacinidae: short-tailed bats
 * Family Molossidae: free-tailed bats
 * Order Carnivora
 * Suborder Fissipedia
 * Superfamily Caniformia
 * Family Canidae: wolves, coyotes, foxes, jackals
 * Family Procyonidae: raccoons, coatis, olingos, kinkajou
 * Family Mustelidae: weasels, otters, badgers
 * Family Ailuridae: red panda
 * Family Mephitidae: skunks
 * Family Ursidae: bears, Giant Panda
 * Superfamily Feliformia
 * Family Felidae: cats
 * Family Herpestidae: mongooses
 * Family Hyaenidae: hyenas, Aardwolf
 * Family Viverridae: civets, genets, linsangs
 * Family Nandiniidae: African palm civet
 * Suborder Pinnipedia
 * Superfamily Otarioidae
 * Family Odobenidae: Walrus
 * Family Otariidae: sea lions
 * Superfamily Phocoidae
 * Family Phocidae: seals
 * Order Pholidota
 * Family Manidae: pangolins
 * Superorder Ungulata
 * Order Afrosoricida
 * Family Tenrecidae: tenrecs
 * Family Chrysochloridae: golden moles
 * Order Macroscelidea
 * Family Macroscelididae: elephant shrews
 * Order Tubulidentata
 * Family Orycteropodidae: Aardvark
 * Order Hyracoidea
 * Family Procaviidae: hyraxes
 * Order Proboscidea
 * Family Elephantidae: elephants
 * Order Sirenia
 * Family Dugongidae: Dugong, Stellar Sea Cow
 * Family Trichechidae: manatees
 * Order Perissodactyla
 * Family Equidae: horses, asses, zebras
 * Family Tapiridae: tapirs
 * Family Rhinocerotidae: rhinceroses
 * Order Artiodactyla
 * Suborder Suiformes (also known as Suina)
 * Family Suidae: pigs, warthogs
 * Family Tayassuidae: peccaries
 * Family Hippopotamidae: hippopotamuses
 * Suborder Tylopoda
 * Family Camelidae: camels, llamas, Vicuna
 * Suborder Ruminantia
 * Family Tragulidae: chevrotains
 * Family Giraffidae: Giraffe, Okapi
 * Family Moschidae: musk deer
 * Family Cervidae: true deer
 * Family Antilocapridae: Pronghorn
 * Family Bovidae: antelope, sheep, goats, buffalo, bison, cattle
 * Order Cetacea
 * Suborder Mysticeti
 * Family Balaenidae: Bowhead and right whales
 * Family Balaenopteridae: rorquals
 * Family Eschrichtiidae: Gray Whale
 * Family Neobalaenidae: Pigmy Right Whale
 * Suborder Odontoceti
 * Family Delphinidae: oceanic dolphins
 * Family Monodontidae: Narwhal, Beluga
 * Family Phocoenidae: porpoises
 * Family Physeteridae: sperm whales
 * Family Platanistoidea: river dolphins
 * Family Ziphiidae: beaked whales