Holotheria

Mammalia is a class of animal within the phylum Chordata. Mammal classification has been through several iterations since Carl Linnaeus initially defined the class. No classification system is universally accepted; McKenna & Bell (1997) and Wilson & Reader (2005) provide useful recent compendiums.^[1] Many earlier ideas from Linnaeus et al. have been completely abandoned by modern taxonomists, among these are the idea that bats are related to birds or that humans represent a group outside of other living things.^[2] 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) taxonomy text 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 Though field work gradually made Simpson's classification outdated, it remained the closest thing to an official classification of mammals. See List of placental mammals and List of monotremes and marsupials for more detailed information on mammal genera and species.

Molecular classification of placentals

Molecular studies by molecular systematists, based on DNA analysis, in the early 21st century have revealed new relationships among mammal families. Classification systems based on molecular studies reveal three major groups or lineages of placental mammals, Afrotheria, Xenarthra, and Boreotheria. which diverged from early common ancestors in the Cretaceous.^[3]

The relationships between these three lineages are contentious, and all three have been proposed as basal in different hypotheses.^[3]^[4]^[5]

The following taxonomy only includes living placentals (infraclass Eutheria):^{[citation needed]}

Atlantogenata

Afrotheria

Clade Afroinsectiphilia
- Order Macroscelidea
  - Family Macroscelididae: (20 species), sengis or elephant shrews (Africa)^[6]
- Order Afrosoricida
  - Family Tenrecidae: (31 species^[7]), tenrecs (Madagascar)
  - Family Potamogalidae: (3 species^[8]), otter-shrews (West and Central Africa)
  - Family Chrysochloridae: (21 species), golden moles (Africa south of the Sahara)
- Order Tubulidentata
  - Family Orycteropodidae: (1 species), aardvark (Africa south of the Sahara)
Clade Paenungulata
- Order Proboscidea
  - Family Elephantidae: (3 species), elephants (Africa, Southeast Asia)
- Order Hyracoidea
  - Family Procaviidae: (4 species), hyraxes, dassies (Africa, Arabia)
- Order Sirenia
  - Family Dugongidae: (1 species), dugong (East Africa, Red Sea, North Australia)
  - Family Trichechidae: (3 species), manatees (tropical Atlantic coasts and adjacent rivers)

Xenarthra

Order Cingulata^[9]
- Family Chlamyphoridae: (14 species), armadillos (Neotropical)
- Family Dasypodidae: (7 species), long-nosed armadillos (Neotropical and Nearctic)
Order Pilosa (=Dasypoda)^[9]
- Suborder Vermilingua (anteaters)
  - Family Cyclopedidae: (1 species), silky anteater (Neotropical)
  - Family Myrmecophagidae: (3 species), anteaters (Neotropical)
- Suborder Folivora (sloths)
  - Family Choloepodidae: (2 species), two-toed sloths (Neotropical)
  - Family Bradypodidae: (4 species), three-toed sloths (Neotropical)

Boreoeutheria

Euarchontoglires

Superorder Euarchonta
- Order Scandentia
  - Family Ptilocercidae (1 species), pen-tailed treeshrews (Southeast Asia)
  - Family Tupaiidae: (19 species), treeshrews (Southeast Asia)
- Mirorder Primatomorpha
  - Order Dermoptera
    - Family Cynocephalidae: (2 species), flying lemurs or colugos (Southeast Asia)
  - Order Primates: lemurs, bushbabies, monkeys, apes (cosmopolitan)
    Aye aye (Daubentonid)
    - Family Cheirogaleidae: (32 species), dwarf lemurs (Madagascar)
    - Family Lemuridae: (22 species), lemurs (Madagascar)
    - Family Lepilemuridae: (26 species), sportive lemurs (Madagascar)
    - Family Indriidae: (19 species), indri and sifakas (Madagascar)
    - Family Daubentoniidae: (1 species), aye-aye (Madagascar area)
    - Family Lorisidae: (9 species), lorises and potto (Africa and Southeast Asia)
    - Family Galagidae: (19 species), galagos (Africa)
      Capuchin monkey (Cebid)
    - Family Tarsiidae: (9 species), tarsiers (Southeast Asia)
    - Family Callitrichidae: (41 species), marmosets and tamarins (South America)
    - Family Cebidae: (14 species), New World monkeys (South America)
    - Family Cercopithecidae: (137 species), Old World monkeys (Africa and Eurasia)
    - Family Hylobatidae: (14 species), gibbons (Southeast Asia)
    - Family Hominidae: (8 species), great apes (worldwide)
Superorder Glires
- Order Lagomorpha: pikas, rabbits, hares (Eurasia, Africa, Americas)
  Arctic hare (Leporid)
  - Family Leporidae: (60 species), rabbits and hares (Eurasia, Africa, Americas)
  - Family Ochotonidae: (30 species), pikas (Holarctic)
- Order Rodentia: rodents (cosmopolitan)
  - Suborder Castorimorpha
    - Family Castoridae: (2 species) beavers (Holarctic)
    - Family Geomyidae: (about 35 species) pocket gophers (North America)
    - Family Heteromyidae: (about 59 species) kangaroo rats and kangaroo mice (North America)
  - Suborder Myomorpha
    - Family Dipodidae: (33 species) jerboas (Africa, Eurasia, North America)
    - Family Zapodidae: (11 species) jumping mice (North America, Asia)
    - Family Sicistidae: (19 species) birch mice (Eurasia)
    - Family Platacanthomyidae: (3 species) spiny dormouse (Southeast Asia)
    - Family Spalacidae: (37 species) zokors, root rats, blind mole rats (Africa, Eurasia)
    - Family Calomyscidae: (8 species) mouse-like hamsters (Asia)
    - Family Nesomyidae: (68 species) old endemic African muroids (Africa, Madagascar)
    - Family Cricetidae: (about 580 species) hamsters, voles, and New World rats and mice (Holarctic, South America)
    - Family Muridae: (about 1,383 species) Old World rats and mice and gerbils (Africa, Eurasia, Australia)
  - Suborder Anomaluromorpha
    - Family Anomaluridae: (6 species) scaly-tailed flying squirrels (Africa)
    - Family Pedetidae: (2 species) springhares or springhaas (Africa)
  - Suborder Hystricomorpha
    - Family Ctenodactylidae: (5 species) gundis (Africa, Asia)
    - Family Diatomyidae: (1 species) Laotian rock rat (Southeast Asia)
    - Family Hystricidae: (11 Species) Old World porcupines (Africa, Asia)
    - Family Bathyergidae: (about 21 species) African mole-rats (Africa)
    - Family Petromuridae: (1 species) rock dassies (Africa)
    - Family Thryonomyidae: (2 species) cane rats (Africa)
    - Family Erethizontidae: (19 species) New World porcupines (New World)
    - Family Chinchillidae: (3 species) chinchillas and viscachas (South America)
    - Family Dinomyidae: (1 species) pacarana (South America)
    - Family Caviidae: (18 species) cavies and capybara (South America)
    - Family Dasyproctidae: (13 species) agoutis and acouchis (South America)
    - Family Cuniculidae: (about 3 species) paca (South America)
    - Family Ctenomyidae: (about 60 species) tuco-tucos (South America)
    - Family Octodontidae: (14 species) degus (South America)
    - Family Abrocomidae: (9 species) chinchilla-rats (South America)
    - Family Echimyidae: spiny rats (South America)
    - Family Capromyidae: (10 species) hutias (South America)
    - Family Heptaxodontidae: giant Hutias (recently extinct)
    - Family Myocastoridae: (57 species) nutrias (South America)
  - Suborder Sciuromorpha
    Mountain beaver (Aplodont)
    - Family Aplodontiidae: (1 species) mountain beaver (western North America)
    - Family Sciuridae: (about 285 species) squirrels, chipmunks, and marmots (cosmopolitan except Australia)
    - Family Gliridae: (29 species) dormice (Africa, Eurasia)

Laurasiatheria

Order Eulipotyphla
- Family Solenodontidae: (2 species) solenodons (Cuba, Hispaniola)
- Family Nesophontidae: nesophontes (West Indies shrews) (recently extinct)
- Family Soricidae: (385 species) shrews (Eurasia, Africa, North America to northern South America)
- Family Talpidae: (59 species) moles, shrew-moles, desmans (Eurasia, North America)
- Family Erinaceidae: (26 species) hedgehogs, gymnures (Eurasia, Africa)
- Family Galericidae: (8 species) moonrats (southeast Asia)
Grandorder Chiroptera
- Order Chiroptera: bats
  - Suborder Yinpterochiroptera
    - Family Pteropodidae: (about 197 species) flying foxes (Africa, Eurasia, Australia)
    - Family Hipposideridae: (84 species) trident bats, leaf-nosed bats
    - Family Rhinolophidae: (106 species) horseshoe bats (Old World)
    - Family Rhinopomatidae: (6 species) mouse-tailed bats (Africa, Southeast Asia)
    - Family Craseonycteridae: (1 species) Kitti's hog-nosed bat (Thailand)
    - Family Megadermatidae: (6 species) false vampire bats (Africa, Southeast Asia, Australia)
  - Suborder Yangochiroptera
    - Family Emballonuridae: (54 species) sac-winged bats (southern continents)
    - Family Nycteridae: (about 15 species) slit-faced bats (Africa, Southeast Asia)
    - Family Mystacinidae: (about 2 species) short-tailed bats (New Zealand)
    - Family Thyropteridae: (5 species) sucker-footed bats (South America)
    - Family Furipteridae: (2 species) smoky bats (South America)
    - Family Noctilionidae: (2 species) fishing bats (South America)
    - Family Mormoopidae: (about 11 species) leaf-chinned bats (South America)
    - Family Phyllostomidae: (192 species) leaf-nosed bats (South America)
    - Family Myzopodidae: (2 species) sucker-footed bats (Madagascar)
    - Family Natalidae: (10 species) funnel-eared bats (South America)
    - Family Molossidae: (about 110 species) free-tailed bats (cosmopolitan)
    - Family Miniopteridae: (about 40 species) long-fingered bats (Africa, Eurasia, Australia)
    - Family Cistugidae: (2 species) wing-gland bats (Southern Africa)
    - Family Vespertilionidae: (over 300 species) vesper bats (cosmopolitan)
Grandorder Ferae
- Order Pholidota
  - Family Manidae: (about 8 species) pangolins, scaly anteaters (Africa, South Asia)
- Order Carnivora: carnivorans (cosmopolitan)
  - Suborder Feliformia
    - Family Nandiniidae: (4 species) African palm civet (Central Africa)
    - Family Prionodontidae: (2 species) Asiatic linsangs (Southeast Asia)
    - Family Felidae: (41 species) cats (cosmopolitan except Australia)
    - Family Viverridae: (33 species) civets, Asiatic palm civets (Africa, Southern Europe, Southeast Asia)
    - Family Herpestidae: (34 species) mongooses (Africa, Asia, Southern Europe)
    - Family Eupleridae: (10 species) Malagasy carnivorans (Madagascar)
    - Family Hyaenidae: (4 species) hyaenas, aardwolf (Africa)
  - Suborder Caniformia
    - Family Canidae: (38 species) dogs (cosmopolitan)
    - Family Ursidae: (8 species) bears (Europe, Asia, New World)
    - Family Otariidae: (15 species) eared seals (cosmopolitan except North Atlantic)
    - Family Odobenidae: (1 species) walrus (Northern North American, Northern Europe, Northern Asia)
    - Family Phocidae: (18 species) true seals (cosmopolitan)
    - Family Ailuridae: (1 species) red panda (South-Central Asia)
    - Family Mephitidae: (12 species) skunks (Southeast Asia, New World)
    - Family Mustelidae: (about 69 species) weasels and relatives (cosmopolitan except Australia)
    - Family Procyonidae: (14 species) ringtails, olingos, kinkajou, raccoons, coatis (New World)
Grandorder Euungulata
- Order Perissodactyla: odd-toed ungulates
  - Family Equidae: (13 species) horses, zebras, donkeys (Africa, West and Central Asia)
  - Family Tapiridae: (3 species) tapirs (Central and South America, Southeast Asia)
  - Family Rhinocerotidae: (5 species) rhinoceroses (Africa, Southeast Asia)
- Order Artiodactyla: even-toed ungulates (now includes Cetaceans)
  - Suborder Suiformes
    - Family Suidae: (18 species) pigs (Africa, Eurasia)
      Pig and piglet
    - Family Tayassuidae: (about 3 species) peccaries (New World)
  - Suborder Tylopoda
    - Family Camelidae: (7 species) camels (South America, Asia)
  - Suborder Ruminantia
    - Family Tragulidae: (10 species) mouse-deer (Africa, Asia)
    - Family Antilocapridae: (1 species) pronghorn (North America)
    - Family Giraffidae: (2-9 species) giraffe and okapi (Africa)
      Giraffe
    - Family Cervidae: (26 species) deer (Holarctic, South America)
    - Family Moschidae: (7 species) musk deer (Asia)
      Muntjac deer
    - Family Bovidae: (143 species) cattle, antelope, sheep, etc. (Africa, Holarctic)
      Pair of Icelandic Sheep
  - Suborder Whippomorpha
    - Family Hippopotamidae: (2 species) hippos (Africa)
    - Infraorder Cetacea
      - Parvorder Mysticeti
        Family Balaenopteridae: (10 species) rorquals and grey whales (cosmopolitan)
        
        Family Balaenidae: (4 species) right and bowhead whales (polar and temperate waters)
        
        Family Eschrichtiidae: (1 species) gray whale (North Pacific and North Atlantic)
        
        Family Neobalaenidae: (1 species) pygmy right whales (southern hemisphere)
      - Parvorder Odontoceti
        Family Delphinidae: (about 37 species) dolphins (cosmopolitan)
        
        Family Monodontidae: (2 species) beluga and narwhal (Arctic, Atlantic, and Pacific)
        
        Family Phocoenidae: (8 species) porpoises (cosmopolitan)
        
        Family Physeteridae: (3 species) sperm whales (cosmopolitan)
        
        Family Kogiidae: (2 species) dwarf sperm whales (cosmopolitan)
        
        Family Platanistidae: (2 species) South Asian river dolphin (Southern Asia)
        
        Family Iniidae: (1-4 species) Amazon River dolphin (South America)
        
        Family Pontoporiidae: (1 species) La Plata River dolphin (South America)
        
        Family Lipotidae: baiji
        
        Family Ziphiidae: (24 species) beaked whales (cosmopolitan)

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 the 6th edition of Vaughan's Mammalogy.^[1] 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 in this classification 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, families are merely listed under the order to which they belong. More detailed relationships among families is presented in the article of each 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 (monitos del monte)
- 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 (bandicoots, echymiperas)
  - Family †Chaeropodidae (pig-footed bandicoot)
- Order Notoryctemorphia (marsupial moles)
  - Family Notoryctidae
- Order Diprotodontia
  - Family Phascolarctidae (koalas)
  - Family Vombatidae (wombats)
  - Family Phalangeridae (brushtail possums and cuscuses)
  - Family Potoroidae (bettongs, potoroos 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)
  - Family Hypsiprymnodontidae (musky rat kangaroo)
Infraclass Eutheria
- Order Afrosoricida
  - Family Tenrecidae (tenrecs)
  - Family Chrysochloridae (golden moles)
- Order Macroscelidea
  - Family Macroscelididae (elephant-shrews
- Order Tubulidentata
  - Family Orycteropodidae (aardvark)
- Order Proboscidea
  - Family Elephantidae (elephants)
- Order Sirenia
  - Family Dugongidae (dugongs, sea cows)
  - Family Trichechidae (manatees)
- Order Hyracoidea
  - Family Procaviidae (hyraxes)
- Order Pilosa
  - Family Bradypodidae (three-toed tree sloths)
  - Family Megalonychidae (two-toed tree sloths)
  - Family Myrmecophagidae (tamanduas and giant anteater)
  - Family Cyclopedidae (silky anteater)
- Order Cingulata
  - Family Dasypodidae (armadillos)
- Order Dermoptera
  - Family Cynocephalidae (colugos)
- Order Scandentia
  - Family Tupaiidae (tree shrews)
  - Family Ptilocercidae (pen-tailed treeshrew)
- Order Primates
  - Family Cheirogaleidae (dwarf lemurs, mouse lemurs)
  - Family Lemuridae (lemurs)
  - Family Lepilemuridae (sportive lemurs)
  - Family Indriidae (wooly lemurs, sifakas)
  - Family Daubentoniidae (aye-aye)
  - Family Lorisidae (lorises)
  - Family Galagidae (bushbabies, galagos)
  - Family Tarsiidae (tarsiers)
  - Family Cebidae (marmosets, tamarins, capuchins, squirrel monkeys)
  - Family Aotidae (night monkeys)
  - Family Pitheciidae (titis, uacaris, sakis)
  - Family Atelidae (howlers, spider monkeys, wooly monkeys)
  - Family Cercopithecidae (Old World monkeys)
  - Family Hylobatidae (gibbons)
  - Family Hominidae (apes, human)
- Order Rodentia
  - Family Aplodontiidae (sewellel or mountain beaver)
  - Family Sciuridae (squirrels)
  - Family Gliridae (dormice)
  - Family Castoridae (beavers)
  - Family Heteromyidae (kangaroo rats, pocket mice)
  - Family Geomyidae (pocket gophers)
  - Family Dipodidae (jerboas, birch mice, jumping mice)
  - Family Platacanthomyidae (tree mice)
  - Family Spalacidae (zokors, bamboo rats, mole rats)
  - Family Calomyscidae (calomyscuses)
  - Family Nesomyidae (pouched rats and mice, climbing and fat mice, etc.)
  - Family Cricetidae (voles, hamsters, New World rats and mice
  - Family Muridae (rats, mice)
  - Family Anomaluridae (scaily-tailed flying squirrels)
  - Family Pedetidae (springhaas, springhares)
  - Family Ctenodactylidae (gundis)
  - Family Diatomyidae (kha-nyous or Laotian rock rat)
  - Family Bathyergidae (mole-rats)
  - Family Hystricidae (African and Asian porcupines)
  - Family Petromuridae (dassie rat)
  - Family Thryonomyidae (can rats)
  - Family Erethizontidae (bristle-spined rat and New World porcupines)
  - Family Chinchillidae (chinchillas, vizcachas)
  - Family Dinomyidae (pacarana)
  - Family Caviidae (cuis, guinea-pigs, cavies, maras, capybaras)
  - Family Dasyproctidae (agoutis, acouchis)
  - Family Cuniculidae (pacas)
  - Family Ctenomyidae (tuco-tucos)
  - Family Octodontidae (degus, rock rats, vizcacha-rats)
  - Family Abrocomidae (chinchilla rats)
  - Family Echimyidae (spiny rats, tree rats, hutias, & coypu)
  - Family †Heptaxodontidae (giant hutias and key mice)
- Order Lagomorpha
  - Family Ochotonidae (pikas)
  - Family †Prolagidae (Sardinian pika)
  - Family Leporidae (rabbits)
- Order Eulipotyphla
  - Family Erinaceidae (hedgehogs, gymnures)
  - Family †Nesophontidae (nesophontes)
  - Family Solenodontidae (solenodons, alamiquis)
  - Family Soricidae (shrews)
  - Family Talpidae (moles, desmans)
- Order Chiroptera
  - Family Pteropodidae (Old World fruit bats, flying foxes)
  - Family Rhinopomatidae (mouse-tailed bats)
  - Family Craseonycteridae (hog-nosed or bumblebee bat)
  - Family Megadermatidae (false vampire bats)
  - Family Rhinolophidae (horseshoe bats)
  - Family Emballonuridae (sac-winged bats)
  - Family Nycteridae (slit-faced bats)
  - Family Myzopodidae (sucker-footed bats)
  - Family Mystacinidae (New Zealand short-tailed bats)
  - Family Thyropteridae (disk-winged bats)
  - Family Furipteridae (smokey bat and thumbless bat)
  - Family Noctilionidae (bulldog bats)
  - Family Mormoopidae (mustached and ghost-faced bats)
  - Family Phyllostomidae (New World leaf-nosed bats)
  - Family Natalidae (funnel-eared bats)
  - Family Molossidae (free-tailed bats)
  - Family Vespertilionidae (evening bats, common bats)
  - Family Miniopteridae (bent-winged or long-fingered bats)
- Order Pholidota
  - Family Manidae (pangolins)
- Order Carnivora
  - Family Felidae (cats)
  - Family Viverridae (civets, genets)
  - Family Eupleridae (falanouc, fossa, Madagascaran mongooses)
  - Family Nandiniidae (African palm civet)
  - Family Herpestidae (mongooses)
  - Family Hyaenidae (hyaenas, aardwolf)
  - Family Canidae (wolves, foxes, jackals)
  - Family Ursidae (bears, giant panda)
  - Family Odobenidae (walrus)
  - Family Otariidae (eared seals, fur seals, sea lions)
  - Family Phocidae (earless seals)
  - Family Mustelidae (weasels, badgers, otters)
  - Family Procyonidae (raccoons, ringtails, coatis)
  - Family Ailuridae (red panda)
- Order Perissodactyla
  - Family Equidae (horses, asses, zebras)
  - Family Tapiridae (tapirs)
  - Family Rhinocerotidae (rhinoceroses)
- Order Artiodactyla
  - Family Suidae (hogs, pigs)
  - Family Tayassuidae (peccaries)
  - Family Hippopotamidae (hippopotamuses)
  - Family Camelidae (camels, vicunas, guanacos, llamas)
  - Family Tragulidae (chevrotains and mouse deer)
  - Family Moschidae (musk deer)
  - Family Cervidae (deer)
  - Family Antilocapridae (pronghorn)
  - Family Giraffidae (giraffe and okapi)
  - Family Bovidae (antelope, bison, cattle, duikers, goats, sheep, etc.)
- Order Cetacea
  - Family Balaenidae (right whales)
  - Family Balaenopteridae (rorquals)
  - Family Eschrichtiidae (gray whales
  - Family Cetotheriidae (pygmy right whale)
  - Family Delphinidae (ocean dolphins)
  - Family Monodontidae (narwhal and beluga)
  - Family Phocoenidae (porpoises)
  - Family Physeteridae (sperm whales)
  - Family Platanistidae (Ganges and Indus river dolphins)
  - Family Iniidae (baiji, franciscana, and Amazon river dolphins)
  - Family Ziphiidae (beaked whales)

McKenna/Bell classification

In 1997, the classification of mammals was revised by Malcolm C. McKenna and Susan K. Bell.^[10] The Classification of Mammals Above the species level, here referred to as the "McKenna/Bell classification", is a comprehensive work on the systematics, relationships, and occurrences of all mammal taxa, living and extinct, down through the rank of genus. The authors worked together as paleontologists at the American Museum of Natural History, New York. McKenna inherited the project from Simpson and, with Bell, constructed a completely updated hierarchical system, covering living and extinct taxa that reflects the historical genealogy of Mammalia.

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 and ranks which fall between classes and orders that are likely to be glossed over by the layman.

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

Extinct groups are represented by †.