Mammals are warm‑blooded animals with hair or fur that suckle their young. They first appeared over 200 million years ago and became the dominant land vertebrates after the extinction of the dinosaurs.
Living mammals are divided into two subclasses: Prototheria and Theria. Prototherians include the egg-laying monotremes. Therians give birth to live young and are further divided into marsupials and placental mammals. This is the classification structure used by iNaturalist.
Subclass Prototheria — Prototherians
Monotremes are the most ancient living mammals. They lay eggs but still produce milk for their young. Today they survive only in Australia and New Guinea.
Order Monotremata — platypuses and echidnas (spiny anteaters) Egg-laying mammals that combine reptile-like reproduction with typical mammal features such as fur and milk production.
Subclass Theria — Therians
Therian mammals give birth to live young rather than laying eggs. They are divided into two major groups: Marsupials and Placental Mammals.
Infraclass Marsupialia — Marsupials
Young are born at an early stage and usually continue developing in a pouch.
Order: Dasyuromorphia – carnivorous marsupials (quolls and Tasmanian devils) Mainly carnivorous Australian marsupials that fill predator roles.
Order: Didelphimorphia – opossums Small to medium American marsupials best known for their ability to “play dead.”
Order: Diprotodontia – kangaroos, wallabies, koalas, wombats and possums The largest marsupial group, mostly plant-eaters found in Australia and nearby regions.
Order: Microbiotheria – monito del monte A single surviving South American species representing an ancient marsupial line.
Order: Notoryctemorphia – marsupial moles Rare, burrowing desert marsupials with very poor eyesight.
Order: Paucituberculata – shrew opossums Small South American marsupials that resemble shrews.
Order: Peramelemorphia – bandicoots and bilbies Ground-dwelling Australian marsupials adapted for digging.
Infraclass Placentalia — Placental Mammals
Young develop fully inside the mother and are nourished through a placenta before birth. This group contains most living mammal species. Placental mammals are divided into four major evolutionary branches, known as superorders.
Superorder Afrotheria — Afromammals
Mammals that evolved primarily in Africa and include several very different-looking groups.
Order: Afrosoricida – tenrecs and golden moles Mainly African insect-eating mammals with diverse lifestyles.
Order: Hyracoidea – hyraxes Small, rock-dwelling mammals from Africa and the Middle East.
Order: Macroscelidea – elephant shrews (sengis) Small, long-nosed African mammals that run quickly on long legs.
Order: Proboscidea – elephants Large African and Asian mammals with trunks and tusks.
Order: Sirenia – manatees and dugongs Large, slow-moving plant-eating mammals that live entirely in water.
Order: Tubulidentata – aardvark A single African species that feeds mainly on ants and termites.
Superorder Euarchontoglires — Primates, Rodents, and Allies
A major group including primates, rodents, and their closest relatives.
Order: Dermoptera — the colugos or “flying lemurs” Tree-dwelling mammals from Southeast Asia that glide between trees using a wide skin membrane.
Order: Lagomorpha – rabbits, hares and pikas Fast-breeding plant-eaters that resemble rodents but belong to a separate order.
Order: Primates – monkeys, apes, lemurs and humans Mammals with grasping hands, forward-facing eyes and relatively large brains.
Order: Rodentia – rodents (mice, rats, squirrels, beavers, porcupines) The largest mammal order, recognised by their constantly growing front teeth for gnawing.
Order: Scandentia – treeshrews Small Southeast Asian mammals that resemble squirrels and are related to primates.
Superorder Laurasiatheria — Ungulates, Carnivores, and Allies
A diverse group including hoofed mammals, carnivores, bats, and insect-eaters.
Order: Artiodactyla – even-toed ungulates and cetaceans (deer, cattle, pigs, giraffes, antelope, whales and dolphins) A major mammal group that includes land-living hoofed animals and their close aquatic relatives, the whales and dolphins.
