Metatheria

Metatheria Temporal range: Early Cretaceous–recent[1][2][3] PreꞒ Ꞓ O S D C P T J K Pg N
Lycopsis longirostris, an extinct sparassodont, a relative of the marsupials
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Subclass:	Theria
Clade:	Metatheria Huxley, 1880
Subgroups
†?Sinodelphys †Holoclemensia †Adinodon †Deltatheroida Marsupialiformes †Adelodelphys †Alphadontidae †Asiadelphia †Sinbadelphys †Camptomus? †Archimetatheria †Stagodontidae †Iqualadelphis †Sparassodonta †Herpetotheriidae †Anatoliadelphyidae †Polydolopimorphia †Peradectidae †Pediomyidae Marsupialia Ameridelphia Australidelphia

Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as well as many extinct non-marsupial relatives.

There are three extant subclasses of mammals, one being metatherians:

1. monotremes: egg laying mammals like the platypus and the echidna,
2. metatheria: marsupials, which includes three American orders (Didelphimorphia, Paucituberculata and Microbiotheria) and four Australasian orders (Notoryctemorphia, Dasyuromorphia, Peramelemorphia and Diprotodontia),^[4] and the
3. eutherians: placental mammals, consisting of four superorders divided into 21 orders.^[5]

Metatherians belong to a subgroup of the northern tribosphenic mammal clade or Boreosphenida. They differ from all other mammals in certain morphologies like their dental formula, which includes about five upper and four lower incisors, a canine, three premolars, and four molars.^[6] Other characters include skeletal and anterior dentition, such as wrist and ankle apomorphies; all metatherians share derived pedal characters and calcaneal features. The earliest known members of the group are from the latter half of the Early Cretaceous in North America. Remains of metatherians have been found on all continents.