(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. 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