Mammalia is a class of vertebrate animals. Members of this class are called mammals. It comprises 5,952 extant species, which are grouped into 163 families, themselves grouped into 27 orders in 3 major divisions. These orders can contain between one and thousands of species, grouped into genera and then into families. Mammals are characterized by the presence of mammary glands which in females produce milk for feeding their young, a neocortex region of the brain, and fur or hair. Mammals are native to all major land masses and the oceans, and can be found worldwide. They live in every habitat on Earth. The basic mammalian body type is quadrupedal, with most mammals using four limbs for terrestrial locomotion, but in some the limbs are adapted for life at sea, in the air, in trees or underground. They range in length from Kitti's hog-nosed bat, at 2 cm (1 in) with no tail, to the blue whale, at 32.6 m (107 ft) long, including tail. The three major divisions of mammals are the infraclass Marsupialia, containing the marsupial animals wherein the young are carried in a pouch; the infraclass Placentalia, for which the fetus is carried in the uterus, and the order Monotremata, containing egg-laying species. Marsupialia contains 333 species, Monotremata contains 5, and Placentalia contains the vast majority of extant mammals at 5,615 species. The majority of mammals, in terms of number of species, are in the two largest orders: Rodentia, or rodents, with 2,360 species, and Chiroptera, or bats, with 1,363. The exact organization of the species is not fixed, with many recent proposals made based on molecular phylogenetic analysis. In addition to the extant mammals, 72 species have been driven extinct since 1500 CE.
Conventions
The author citation for the species or genus is given after the scientific name; parentheses around the author citation indicate that this was not the original taxonomic placement. Range maps are provided wherever possible; if a range map is not available, a description of the collective range of species in that genera is provided. Ranges are based on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species unless otherwise noted. All extinct genera or species listed alongside extant species went extinct after 1500 CE, and are indicated by a dagger symbol "†".
Classification The class Mammalia consists of 5,942 extant species grouped into 1,295 genera belonging to 163 families. This does not include hybrid species or extinct prehistoric species. Modern molecular studies indicate that the 163 families can be grouped into 27 orders; these orders are divided into 3 major groupings: Marsupialia, an infraclass containing 7 orders of mammals which give birth to relatively undeveloped young that often reside in a pouch located on their mothers' abdomen for a time; Placentalia, an infraclass containing 19 orders of mammals that have fetuses that are carried in the uterus, and Monotremata, an order of egg-laying mammals. Within these groupings, the orders are organized into named clades, and some of these orders are subdivided into named suborders. An additional 72 species have been driven extinct since 1500 CE: 15 in Marsupialia and 57 in Placentalia.
Mammals The following classification is based on the taxonomy described by Mammal Species of the World (2005), with augmentation by generally accepted proposals made since using molecular phylogenetic analysis, as supported by both the IUCN and the American Society of Mammalogists.
Infraclass Marsupialia
Marsupialia is one of the three main divisions of mammals, and contains 334 extant species. It is distinguished from the other two groups in that marsupials give birth to relatively undeveloped young that often reside in a pouch located on their mothers' abdomen for a certain amount of time. It is divided into two groupings: the superorder Australidelphia and Ameridelphia, which was previously considered a superorder but is now regarded as a paraphyletic group. Ameridelphia contains 99 extant species in 2 orders, each containing a single family: Didelphimorphia, or the opossums, and Paucituberculata, or the shrew opossums. Australidelphia contains 235 extant species in 18 families, grouped into 5 orders: Dasyuromorphia, or the Australian carnivorous marsupials; Diprotodontia, or the kangaroos and possums; Microbiotheria, or the monito del montes; and Notoryctemorphia, or the marsupial moles; and Peramelemorphia, or the bandicoots and bilbies. One additional species in Ameridelphia and twelve in Australidelphia were driven extinct in modern times.
Ameridelphia
Didelphimorphia
Members of the Didelphimorphia order are called didelphimorphs or opossums. They are found in North and South America, Australia, and southeastern Asia and are omnivorous, eating insects, small vertebrates, and vegetation. Didelphimorphia comprises a single family of 92 extant species in 18 genera. One additional species was driven extinct in modern times.
Paucituberculata Members of the Paucituberculata order are called paucituberculatans or shrew opossums. They are found in western South America and are omnivorous, eating larva, small vertebrates, and vegetation. Paucituberculata comprises a single family of seven extant species in three genera.
Superorder Australidelphia
Dasyuromorphia
Members of the Dasyuromorphia order are called dasyuromorphs or Australian carnivorous marsupials and include the marsupial shrews and the numbat. They are found in Australia and New Guinea and are carnivorous, eating a wide variety of vertebrates and invertebrates. Dasyuromorphia comprises 2 extant families containing 71 extant species in 17 genera. Two additional species, one of which comprised an entire family, were driven extinct in modern times.
Diprotodontia
Members of the Diprotodontia order are called diprotodonts and include kangaroos, wallabies, potoroos, possums, the koala, and wombats. They are found in Australia and southeastern Asia and are omnivorous, but primarily eat a wide variety of vegetation and invertebrates. Diprotodontia comprises 11 families containing 139 extant species in 39 genera. These families are divided between three suborders: Macropodiformes, containing the kangaroos, wallabies, and potoroos; Phalangeriformes, or the possums; and Vombatiformes, or the koala and wombats. Nine additional kangaroo and potoroo species were driven extinct in modern times.
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