Metatheria is a grouping within the animal class Mammalia. First proposed by Thomas Henry Huxley in 1880, it is nearly synonymous with the earlier taxon Marsupialia (Illiger, 1811) though it is slightly wider. It also contains the nearest ancestors of marsupial mammals. Orders Subclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia The mammals are the class of vertebrate animals characterized by the presence of mammary glands... Thomas Huxley Thomas Henry Huxley F.R.S. (May 4, 1825 – June 29, 1895) was a British biologist, known as Darwins Bulldog for his defence of Charles Darwins theory of evolution. ... 1880 was a leap year starting on Thursday (see link for calendar). ... Orders Superorder Ameridelphia Didelphimorphia Paucituberculata Superorder Australidelphia Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Marsupials are mammals in which the female typically has a pouch (called the marsupium, from which the name Marsupial derives) in which it rears its young through early infancy. ... Johann Karl Wilhelm Illiger (November 19, 1775 - May 1813) was a German entomologist. ... 1811 was a common year starting on Tuesday (see link for calendar). ...

The earliest known representatives are known from the uppermost Lower Cretaceous of North America. The Cretaceous period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic period (about 146 MYA) to the beginning of the Paleocene epoch of the Tertiary period (65. ... World map showing location of North America A satellite composite image of North America North America is a continent in the northern hemisphere, bounded on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the south by the Caribbean Sea, and on the west...

The closest living relatives of the metatheres are within Eutheria (also erected by Huxley in 1880). Both are sometimes united Infraclasses within the Subclass of Theria (Parker and Haswell, 1897), which contains all living mammals except monotremes. Eutheria is a taxon (specifically, an infraclass) nearly synonymous with Placentalia, containing the placental mammals and the nearest ancestors of placental mammals (which are known only from the fossil record). ... Scientific classification or biological classification refers to how biologists group and categorize extinct and living species of organisms. ... In object-oriented programming, subclass is a class that is derived from another class or classes. ... Infraclasses Eutheria Metatheria Theria is a subclass of advanced mammals that give birth to live young without using a shelled egg. ... Families Kollikodontidae (extinct) Ornithorhynchidae - Platypus Tachyglossidae - Echidnas Steropodontidae (extinct) Monotremes (< monos, single + trema, hole; refers to the cloaca) are mammals that are best known for laying eggs, instead of giving birth to live young like marsupials (Metatheria) and placental mammals (Eutheria). ...

Reference

• McKenna MC & Bell SK, (1997), Classification of Mammals Above the Species Level. Columbia University Press.