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Marsupials are any members of the
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
ian
infraclass In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, ...
Marsupialia. All extant marsupials are endemic to
Australasia Australasia is a region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and phenomena of the Earth and planets. ...

Australasia
,
Wallacea in blue has been used to separate Wallacea into a western part pertaining to Asia Asia () is a landmass variously described as part of Eurasia Eurasia () is the largest continent A continent is any of several large landmasse ...

Wallacea
and the
Americas The Americas (also collectively called America) is a landmass comprising the totality of North America, North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. Along with th ...

Americas
. A distinctive characteristic common to most of these
species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individu ...

species
is that the young are carried in a pouch. Marsupials include
opossum Opossums () are members of the marsupial Order (biology), order Didelphimorphia () Endemism, endemic to the Americas. The largest order of marsupials in the Western Hemisphere, it comprises 120+ species in 19 Genus, genera. Opossums originated in ...

opossum
s,
Tasmanian devil The Tasmanian devil (''Sarcophilus harrisii'') is a carnivorous marsupial Marsupials are any members of the mammalian Class (biology), infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A ...
s,
kangaroo The kangaroo is a marsupial from the family Macropodidae (macropods, meaning "large foot"). In common use the term is used to describe the largest species from this family, the red kangaroo, as well as the antilopine kangaroo, eastern grey k ...

kangaroo
s,
koala The koala or, inaccurately, koala bear (''Phascolarctos cinereus''), is an arboreal herbivorous marsupial native to Australia. It is the only Extant taxon, extant representative of the family Phascolarctidae and its closest living relative ...

koala
s,
wombat Wombats are short-legged, muscular quadrupedal marsupials that are native to Australia. They are about in length with small, stubby tails and weigh between . All three of the extant species are members of the family (biology), family Vombati ...

wombat
s,
wallabies
wallabies
,
bandicoot Bandicoots are a group of more than 20 species of small to medium-sized, terrestrial marsupial omnivores in the order Peramelemorphia. They are endemic to the Australia–New Guinea region, including the Bismarck Archipelago and, marginally, in ...

bandicoot
s, and the extinct
thylacine The thylacine ( , or , also ) (''Thylacinus cynocephalus'') is an extinct carnivorous marsupial that was native to the Mainland Australia, Australian mainland and the islands of Tasmania and New Guinea. The last known live animal was capture ...

thylacine
. Marsupials represent the
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants - on a phylogenetic tree. R ...

clade
originating from the
last common ancestor In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms ...
of extant
metatheria Metatheria is a mammalian clade A clade (), also known as a monophyletic group or natural group, is a group of organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All or ...
ns, the group containing all mammals more closely related to marsupials than to
placentals
placentals
. They give birth to relatively undeveloped young that often reside in a pouch located on their mothers' abdomen for a certain amount of time. Close to 70% of the 334
extant Extant is the opposite of the word extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the endling, last individual o ...
species occur on the
Australian continent The continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven regions are commonly regarded as continents. Ordered from largest in ...
(the mainland,
Tasmania Tasmania (), abbreviated as TAS, is an island An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atol ...
,
New Guinea New Guinea (; Hiri Motu Hiri Motu, also known as Police Motu, Pidgin Motu, or just Hiri, is a language A language is a structured system of communication used by humans, including speech (spoken language), gestures (Signed language, sign ...

New Guinea
and nearby islands). The remaining 30% are found in the Americas—primarily in
South America South America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continent ...

South America
, thirteen in
Central America Central America ( es, América Central, , ''Centroamérica'' ) is a region of the Americas The Americas (also collectively called America) is a landmass comprising the totality of North North is one of the four compass points or ...

Central America
, and one species, the
Virginia opossum The Virginia opossum (''Didelphis virginiana''), commonly known as the North American opossum, is the only opossum The opossum ( or ) is a marsupial of the Order (biology), order Didelphimorphia () Endemism, endemic to the Americas. The larges ...
, in North America, north of Mexico. The word ''marsupial'' comes from '' marsupium'', the technical term for the abdominal pouch. It, in turn, is borrowed from Latin and ultimately from the ancient Greek , meaning "pouch".


Taxonomy

Marsupials are taxonomically identified as members of
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
ian
infraclass In biological classification In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, ...
Marsupialia, first described as a family under the order Pollicata by German zoologist
Johann Karl Wilhelm Illiger Johann Karl Wilhelm Illiger (19 November 1775 – 10 May 1813) was a Germany, German entomologist and zoologist. Illiger was the son of a merchant in Braunschweig. He studied under the entomologist Johann Christian Ludwig Hellwig, Johann Hellwig, ...
in his 1811 work ''Prodromus Systematis Mammalium et Avium''. However, James Rennie, author of ''The Natural History of Monkeys, Opossums and Lemurs'' (1838), pointed out that the placement of five different groups of mammals –
monkey Monkey is a common name that may refer to certain groups or species of simian mammals of infraorder Simiiformes. The term is applied descriptively to groups of primates, such as families of New World monkeys and Old World monkeys. Many monk ...

monkey
s,
lemur Lemurs ( ) (from Latin ''lemures'' – ghosts or spirits) are wet-nosed primates of the superfamily SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid s ...

lemur
s,
tarsier Tarsiers are haplorrhine primates of the Family (biology), family Tarsiidae, which is itself the lone extant family within the infraorder Tarsiiformes. Although the group was once more widespread, all of its species living today are found in the i ...

tarsier
s,
aye-aye The aye-aye (''Daubentonia madagascariensis'') is a long-fingered lemur Lemurs ( ) (from Latin ''lemures'' – ghosts or spirits) are wet-nosed primates of the superfamily SUPERFAMILY is a database and search platform of structural and fu ...

aye-aye
s and marsupials (with the exception of kangaroos, that were placed under the order Salientia) – under a single order (Pollicata) did not appear to have a strong justification. In 1816, French zoologist
George Cuvier Jean Léopold Nicolas Frédéric, Baron Cuvier (; 23 August 1769 – 13 May 1832), known as Georges Cuvier, was a French naturalist Natural history is a domain of inquiry involving organisms, including animals, fungus, fungi, and plants, in ...
classified all marsupials under the order Marsupialia. In 1997, researcher J. A. W. Kirsch and others accorded infraclass rank to Marsupialia. There are two primary divisions: American marsupials (
Ameridelphia Ameridelphia is traditionally a superorder that includes all marsupial Marsupials are any members of the mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class ...
) and Australian marsupials (
Australidelphia Australidelphia is the superorder that contains roughly three-quarters of all marsupials, including all those native to Australasia and a single species from South America. All other American marsupials are members of the Ameridelphia. Analysis of ...
) of which one, the
monito del monte The monito del monte or colocolo opossum, ''Dromiciops gliroides'', also called ''chumaihuén'' in Mapudungun, is a diminutive marsupial native only to southwestern South America South America is a continent entirely in the Western Hemi ...
, is actually native to South America.


Classification

Marsupialia is further divided as follows: – Extinct * Superorder
Ameridelphia Ameridelphia is traditionally a superorder that includes all marsupial Marsupials are any members of the mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class ...
** Order Didelphimorphia (127 species) *** Family Didelphidae: opossums ** Order
Paucituberculata Paucituberculata is an order of South America South America is a entirely in the and mostly in the , with a relatively small portion in the . It can also be described as the southern of a single continent called (see the ). The ref ...
(seven species) *** Family
Caenolestidae The family Caenolestidae contains the seven surviving species of shrew opossum: small, shrew-like marsupials that are confined to the Andes The Andes, Andes Mountains or Andean Mountains ( es, Cordillera de los Andes) are the List of mountai ...

Caenolestidae
:
shrew opossum The family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to maintain the well-being of i ...
s * Superorder
Australidelphia Australidelphia is the superorder that contains roughly three-quarters of all marsupials, including all those native to Australasia and a single species from South America. All other American marsupials are members of the Ameridelphia. Analysis of ...
** Order Microbiotheria (three species) *** Family Microbiotheriidae: monitos del monte ** Order †
Yalkaparidontia ''Yalkaparidon'' is an extinct Extinction is the termination of a kind of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#B ...
(''incertae sedis'') ** Order
Dasyuromorphia Dasyuromorphia (, meaning "hairy tail" in Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. ...
(75 species) *** Family † Thylacinidae:
thylacine The thylacine ( , or , also ) (''Thylacinus cynocephalus'') is an extinct carnivorous marsupial that was native to the Mainland Australia, Australian mainland and the islands of Tasmania and New Guinea. The last known live animal was capture ...

thylacine
*** Family
Dasyuridae The Dasyuridae are a family of marsupial Marsupials are any members of the mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized ...
:
antechinus ''Antechinus'' (// ('ant-echinus')) is a genus Genus (plural genera) is a taxonomic rank Taxonomy (general) is the practice and science of classification of things or concepts, including the principles that underlie such classification. The ...
es,
quoll Quolls (; genus ''Dasyurus'') are carnivorous A carnivore , meaning "meat Meat is animal flesh that is eaten as food. Humans have hunted and killed animals for meat since prehistoric times. The advent of civilization allowed the dom ...
s,
dunnart Dunnart is a common name for species of the genus ''Sminthopsis'', narrow-footed marsupial Marsupials are any members of the mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the cla ...
s,
Tasmanian devil The Tasmanian devil (''Sarcophilus harrisii'') is a carnivorous marsupial Marsupials are any members of the mammalian Class (biology), infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A ...
, and relatives *** Family Myrmecobiidae:
numbat The numbat (''Myrmecobius fasciatus''), also known as the noombat or walpurti, is an insectivorous A robber fly eating a hoverfly The giant anteater, a large insectivorous mammal An insectivore is a Carnivore, carnivorous plant or ani ...

numbat
** Order
Notoryctemorphia Notoryctidae is a family of mammals, allying several extant and fossil species of Australia. The group appear to have diverged from other marsupial Marsupials are any members of the mammal Mammals (from Latin language, Latin , 'breast ...
(two species) *** Family
Notoryctidae Notoryctidae is a family of mammals, allying several extant and fossil species of Australia. The group appear to have diverged from other marsupial Marsupials are any members of the mammal Mammals (from Latin language, Latin , 'breast ...
:
marsupial mole Marsupial moles, the Notoryctidae , are highly specialized marsupial mammals, known from two species found at the Australian interior. * ''Notoryctes typhlops'' (southern marsupial mole, known as the ''itjaritjari'' by the Pitjantjatjara and Ya ...

marsupial mole
s ** Order
Peramelemorphia The Order (biology), order Peramelemorphia includes the bandicoots and bilby, bilbies; it equates approximately to the mainstream of marsupial omnivores. All members of the order are endemic to the twin land masses of Australia-New Guinea and mo ...

Peramelemorphia
(24 species) *** Family
Thylacomyidae ''Macrotis'' is a genus of desert-dwelling marsupial omnivores known as bilbies or rabbit-bandicoots; Unabridged they are members of the order Peramelemorphia. At the time of History of Australia, European colonisation of Australia, there wer ...
: *** Family †Chaeropodidae:
pig-footed bandicoot ''Chaeropus'', known as the pig-footed bandicoots, is a genus of small mammals that became extinct during the twentieth century. They were unique marsupials Marsupials are any members of the mammal Mammals (from Latin language, Latin , ...

pig-footed bandicoot
s *** Family
Peramelidae The marsupial Marsupials are any members of the mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary ...
:
bandicoot Bandicoots are a group of more than 20 species of small to medium-sized, terrestrial marsupial omnivores in the order Peramelemorphia. They are endemic to the Australia–New Guinea region, including the Bismarck Archipelago and, marginally, in ...

bandicoot
s and allies ** Order
Diprotodontia Diprotodontia (, from Greek "two forward teeth") is the largest extant order of marsupials, with about 155 species, including the kangaroos, wallabies, possums, koala The koala or, inaccurately, koala bear (''Phascolarctos cinereus'' ...
(137 species) *** Suborder
Vombatiformes The Vombatiformes are one of the three suborder In biological classification, the order ( la, wikt:ordo#Latin, ordo) is # a taxonomic rank used in the classification of organisms and recognized by the nomenclature codes. The well-known ranks in ...
**** Family Vombatidae:
wombat Wombats are short-legged, muscular quadrupedal marsupials that are native to Australia. They are about in length with small, stubby tails and weigh between . All three of the extant species are members of the family (biology), family Vombati ...

wombat
s **** Family
Phascolarctidae The Phascolarctidae (''φάσκωλος (phaskolos)'' - pouch or bag, ''ἄρκτος (arktos)'' - bear, from the Greek ''phascolos'' + ''arctos'' meaning pouched bear) is a family (biology), family of Marsupialia, marsupials of the order Diproto ...
:
koala The koala or, inaccurately, koala bear (''Phascolarctos cinereus''), is an arboreal herbivorous marsupial native to Australia. It is the only Extant taxon, extant representative of the family Phascolarctidae and its closest living relative ...

koala
s **** Family Diprotodontidae: Giant wombats **** Family
Palorchestidae Palorchestidae is an extinct family of diprotodont marsupial Marsupials are any members of the mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia ( ...
: Marsupial tapirs **** Family
Thylacoleonidae Thylacoleonidae is a family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of socie ...
: marsupial lions *** Suborder
Phalangeriformes Phalangeriformes is a paraphyletic suborder of about 70 species of small to medium-sized arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some ...

Phalangeriformes
**** Family
Acrobatidae The Acrobatidae are a small family of gliding marsupials containing two genera, each with a single species, the feathertail glider (''Acrobates pygmaeus'') from Australia Australia, officially the Commonwealth of Australia, is a Sover ...
:
feathertail glider The feathertail glider (''Acrobates pygmaeus''), also known as the pygmy gliding possum, pygmy glider, pygmy phalanger, flying phalanger and flying mouse, is a species of marsupial native to eastern Australia Australia, officially the Co ...

feathertail glider
and feather-tailed possum **** Family
Burramyidae The pygmy possums are a family of small Phalangeriformes, possums that together form the marsupial family Burramyidae. The five extant species of pygmy possum are grouped into two genus, genera. Four of the species are endemism, endemic to Austra ...
:
pygmy possum The pygmy possums are a family of small possums Possum may refer to: Animals * Opossum, or possum, an order (Didelphimorphia) of marsupials native to the Americas ** Common opossum, native to Central and South America ** Virginia opossum, nativ ...
s **** Family † Ektopodontidae: sprite possums **** Family
Petauridae The family (biology), family Petauridae includes 11 medium-sized Phalangeriformes, possum species: four striped possums, six species of wrist-winged gliders in the genus ''Petaurus'' and Leadbeater's possum, which has only vestigial gliding membra ...
:
striped possum The striped possum or common striped possum (''Dactylopsila trivirgata'') is a member of the marsupial family (biology), family Petauridae. The species is black with three white stripes running head to tail, and its head has white stripes that for ...
, Leadbeater's possum,
yellow-bellied glider The yellow-bellied glider (''Petaurus australis''), also known as the fluffy glider, is an arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some ...
,
sugar glider The sugar glider (''Petaurus breviceps'') is a small, omnivorous An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores di ...

sugar glider
,
mahogany glider The mahogany glider (''Petaurus gracilis'') is an endangered gliding possum
,
squirrel glider The squirrel glider (''Petaurus norfolcensis'') is a nocturnal Nocturnality is an ethology, animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, d ...
**** Family
Phalangeridae The Phalangeridae are a family of mostly nocturnal Nocturnality is an animal behavior Ethology is the scientific Science (from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic bra ...
: s and
cuscus Cuscus ( or ) is the common name Common may refer to: Places * Common, a townland in County Tyrone, Northern Ireland * Boston Common Boston Common (also known as the Common) is a central public park in downtown Boston, Massachusetts. It is so ...

cuscus
es **** Family
Pseudocheiridae Pseudocheiridae is a family of arboreal Arboreal locomotion is the locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exc ...
: and relatives **** Family Tarsipedidae:
honey possum The honey possum or noolbenger, ''Tarsipes rostratus'', is a tiny species of marsupial that feeds on the nectar and pollen of a diverse range of flowering plants. Found in southwest Australia, it is an important pollinator for such plants as ''Ba ...
*** Suborder
Macropodiformes The Macropodiformes , also known as macropods, are one of the three suborder In biological classification, the order ( la, wikt:ordo#Latin, ordo) is # a taxonomic rank used in the classification of organisms and recognized by the nomenclature c ...
**** Family
Macropodidae Macropodidae is a family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of society ...
:
kangaroo The kangaroo is a marsupial from the family Macropodidae (macropods, meaning "large foot"). In common use the term is used to describe the largest species from this family, the red kangaroo, as well as the antilopine kangaroo, eastern grey k ...

kangaroo
s, , and relatives **** Family
Potoroidae Potoroidae is a family of marsupial Marsupials are any members of the mammalian Class (biology), infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most ...
:
potoroo Potoroo is a common name for species of ''Potorous'', a genus of smaller marsupials. They are allied to the Macropodiformes, the suborder of kangaroo, wallaby, and other rat-kangaroo genera. All three extant species are Threatened species, threat ...
s, rat kangaroos,
bettong Bettongs, species of the genus ''Bettongia'', are potoroine marsupials once common in Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (conti ...

bettong
s **** Family
Hypsiprymnodontidae The Hypsiprymnodontidae are a family (biology), family of Macropodiformes, macropods, one of two families containing animals commonly referred to as rat-kangaroos. The single known extant genus and species in this family, the musky rat-kangaroo, ...
: **** Family
Balbaridae Balbaridae is an extinct Extinction is the termination of a kind of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies the Life#Biology ...
: basal quadrupedal kangaroos


Phylogenetic relationships

Comprising over 300 extant species, several attempts have been made to accurately interpret the
phylogenetic In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...

phylogenetic
relationships among the different marsupial orders. Studies differ on whether Didelphimorphia or Paucituberculata is the
sister group In phylogenetics, a sister group or sister taxon comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and taxon B are sister groups to eac ...
to all other marsupials. Though the order Microbiotheria (which has only one species, the
monito del monte The monito del monte or colocolo opossum, ''Dromiciops gliroides'', also called ''chumaihuén'' in Mapudungun, is a diminutive marsupial native only to southwestern South America South America is a continent entirely in the Western Hemi ...
) is found in South America, morphological similarities suggest it is closely related to Australian marsupials. Molecular analyses in 2010 and 2011 identified Microbiotheria as the sister group to all Australian marsupials. However, the relations among the four Australidelphid orders are not as well understood. The
cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics Cladistics (, from Greek language, Greek , ''kládos'', "branch") is an approach to Taxonomy (biology), biological classification in whi ...

cladogram
below, depicting the relationships among the various marsupial orders, is based on a 2015 phylogenetic study. DNA evidence supports a South American origin for marsupials, with Australian marsupials arising from a single
Gondwana Gondwana () or Gondwanaland was a supercontinent In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (ge ...

Gondwana
n migration of marsupials from South America, across Antarctica, to Australia. There are many small
arboreal Arboreal locomotion is the locomotion Locomotion means the act or ability of an entity or person to transport or move oneself from place to place. Locomotion or Loco-Motion may refer to: Motion * Motion (physics) *Specific types of motion ** A ...
species in each group. The term "
opossum Opossums () are members of the marsupial Order (biology), order Didelphimorphia () Endemism, endemic to the Americas. The largest order of marsupials in the Western Hemisphere, it comprises 120+ species in 19 Genus, genera. Opossums originated in ...

opossum
" is used to refer to American species (though "possum" is a common abbreviation), while are properly called "possums".


Anatomy

Marsupials have the typical characteristics of
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
s—e.g., mammary glands, three , and true
hair Hair is a protein filament In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Ph ...

hair
. There are, however, striking differences as well as a number of anatomical features that separate them from
Eutheria Eutheria (; from Greek , 'good, right' and , 'beast'; ) is the clade consisting of all Theria, therian mammals that are more closely related to Placentalia, placentals than to Marsupial, marsupials. Eutherians are distinguished from noneuther ...

Eutheria
ns. In addition to the front pouch, which contains multiple
teat A teat is the projection from the mammary gland A mammary gland is an exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word ''mamma'', "breast". The mammary glands a ...
s for the sustenance of their young, marsupials have other common structural features.
Ossified 300 px, Bone is broken down by osteoclasts, and rebuilt by osteoblasts, both of which communicate through cytokine ( IGF) signalling.">Insulin-like_growth_factor.html" ;"title="TGF-β, Insulin-like growth factor">IGF) signalling. Ossification ( ...
patella The patella, also known as the kneecap, is a flat, rounded triangular bone which articulates with the femur (thigh bone) and covers and protects the anterior articular surface of the knee joint. The patella is found in many tetrapods, such as mo ...
e are absent in most modern marsupials (though a small number of exceptions are reported) and epipubic bones are present. Marsupials (and
monotreme Monotremes are prototherian mammals of the order Monotremata. They are one of the three main groups of living mammals, along with placentals (Eutheria) and marsupials (Metatheria). Monotremes are typified by structural differences in their brai ...
s) also lack a gross communication (
corpus callosum The corpus callosum (Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Repu ...

corpus callosum
) between the right and left brain hemispheres.


Skull and teeth

The skull has peculiarities in comparison to placental mammals. In general, the skull is relatively small and tight. Holes (''foramen lacrimale'') are located in the front of the orbit. The cheekbone is enlarged and extends farther to the rear. The angular extension (''processus angularis'') of the lower jaw is bent toward the center. Another feature is the hard palate which, in contrast to the placental mammals' foramina, always have more openings. The teeth differ from that of placental mammals, so that all
taxa In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechani ...
except
wombat Wombats are short-legged, muscular quadrupedal marsupials that are native to Australia. They are about in length with small, stubby tails and weigh between . All three of the extant species are members of the family (biology), family Vombati ...

wombat
s have a different number of incisors in the upper and lower jaws. The early marsupials had a dental formula from , that is, per quadrant; they have five (maxillary) or four (mandibular) incisors, one canine, three premolars and four molars, for a total of 50 teeth. Some taxa, such as the
opossum Opossums () are members of the marsupial Order (biology), order Didelphimorphia () Endemism, endemic to the Americas. The largest order of marsupials in the Western Hemisphere, it comprises 120+ species in 19 Genus, genera. Opossums originated in ...

opossum
, have the original number of teeth. In other groups the number of teeth is reduced. The dental formula for
Macropodidae Macropodidae is a family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of society ...
(kangaroos and wallabies etc.) is 3/1 – (0 or 1)/0 – 2/2 – 4/4. Marsupials in many cases have 40 to 50 teeth, significantly more than placental mammals. The second set of teeth grows in only at the 3rd premolar site and back; all teeth more anterior to that erupt initially as permanent teeth.


Torso

Few general characteristics describe their skeleton. In addition to unique details in the construction of the ankle, epipubic bones (''ossa epubica'') are observed projecting forward from the pubic bone of the pelvis. Since these are present in males and pouchless species, it is believed that they originally had nothing to do with reproduction, but served in the muscular approach to the movement of the hind limbs. This could be explained by an original feature of mammals, as these epipubic bones are also found in
monotreme Monotremes are prototherian mammals of the order Monotremata. They are one of the three main groups of living mammals, along with placentals (Eutheria) and marsupials (Metatheria). Monotremes are typified by structural differences in their brai ...
s. Marsupial reproductive organs differ from the placental mammals. For them, the reproductive tract is doubled. The females have two uteri and two vaginas, and before birth, a birth canal forms between them, the median vagina. The males have a split or double penis lying in front of the scrotum. A pouch is present in most, but not all, species. Many marsupials have a permanent bag, whereas in others the pouch develops during gestation, as with the
shrew opossum The family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to maintain the well-being of i ...
, where the young are hidden only by skin folds or in the fur of the mother. The arrangement of the pouch is variable to allow the offspring to receive maximum protection. Locomotive kangaroos have a pouch opening at the front, while many others that walk or climb on all fours have the opening in the back. Usually, only females have a pouch, but the male
water opossum The water opossum (''Chironectes minimus''), also locally known as the yapok (), is a marsupial Marsupials are any members of the mammalian Class (biology), infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea an ...
has a pouch that is used to accommodate his genitalia while swimming or running.


General and convergences

Marsupials have adapted to many habitats, reflected in the wide variety in their build. The largest living marsupial, the
red kangaroo The red kangaroo (''Osphranter rufus'') is the largest of all kangaroo The kangaroo is a marsupial Marsupials are any members of the mammalian Class (biology), infraclass Marsupialia. All extant marsupials are endemic to Australasia, ...

red kangaroo
, grows up to in height and in weight, but extinct genera, such as ''
Diprotodon ''Diprotodon'' is an extinct genus of gigantic quadrupedal marsupial native to Australia during the Pleistocene The Pleistocene ( , often colloquially referred to as the ''Ice Age'') is the geological Epoch (geology), epoch that lasted from abo ...

Diprotodon
'', were significantly larger and heavier. The smallest members of this group are the
marsupial mice Marsupials are any members of the mammal Mammals (from Latin language, Latin , 'breast') are a group of vertebrate animals constituting the class (biology), class Mammalia (), and characterized by the presence of mammary glands which in ...
, which often reach only in body length. Some species resemble placental mammals and are examples of
convergent evolution Convergent evolution is the independent evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; eit ...
. The extinct ''
Thylacine The thylacine ( , or , also ) (''Thylacinus cynocephalus'') is an extinct carnivorous marsupial that was native to the Mainland Australia, Australian mainland and the islands of Tasmania and New Guinea. The last known live animal was capture ...

Thylacine
'' strongly resembled the placental wolf, hence its nickname "Tasmanian wolf". The ability to glide evolved in both marsupials (as with
sugar glider The sugar glider (''Petaurus breviceps'') is a small, omnivorous An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores di ...

sugar glider
s) and some placental mammals (as with
flying squirrel Flying squirrels (scientifically known as Pteromyini or Petauristini) are a tribe The term tribe is used in many different contexts to refer to a category of human Humans (''Homo sapiens'') are the most populous and widespread species ...

flying squirrel
s), which developed independently. Other groups such as the kangaroo, however, do not have clear placental counterparts, though they share similarities in lifestyle and ecological niches with
ruminant Ruminants (suborder Ruminantia) are large ungulate, hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by Enteric fermentation, fermenting it in a specialized stomach prior to digestion, princi ...
s.


Reproductive system

Marsupials' reproductive systems differ markedly from those of placental mammals. During embryonic development, a choriovitelline placenta forms in all marsupials. In bandicoots, an additional chorioallantoic placenta forms, although it lacks the chorionic villi found in eutherian placentas. The evolution of reproduction in marsupials, and speculation about the ancestral state of mammalian reproduction, have engaged discussion since the end of the 19th century. Both sexes possess a cloaca, which is connected to a urogenital sac used to store waste before expulsion. The urinary bladder, bladder of marsupials functions as a site to concentrate urine and empties into the common urogenital sinus in both females and males.


Male reproductive system

Most male marsupials, except for macropodidae, macropods and
marsupial mole Marsupial moles, the Notoryctidae , are highly specialized marsupial mammals, known from two species found at the Australian interior. * ''Notoryctes typhlops'' (southern marsupial mole, known as the ''itjaritjari'' by the Pitjantjatjara and Ya ...

marsupial mole
s, have a bifurcated penis, separated into two columns, so that the penis has two ends corresponding to the females' two vaginas. The penis is used only during copulation (zoology), copulation, and is separate from the urinary tract. It curves forward when erect, and when not erect, it is retracted into the body in an S-shaped curve. Neither marsupials nor monotremes possess a baculum. The shape of the glans penis varies among marsupial species. The male
thylacine The thylacine ( , or , also ) (''Thylacinus cynocephalus'') is an extinct carnivorous marsupial that was native to the Mainland Australia, Australian mainland and the islands of Tasmania and New Guinea. The last known live animal was capture ...

thylacine
has a pouch that acts as a protective sheath, covering his external reproductive organs while he runs through thick brush. The shape of the urethral grooves of the males' genitalia is used to distinguish between ''Monodelphis brevicaudata'', ''Monodelphis domestica'', and ''Monodelphis americana''. The grooves form 2 separate channels that form the ventral and dorsal folds of the erectile tissue. Several species of dasyurid marsupials can also be distinguished by their penis morphology. The only accessory sex glands marsupials possess are the prostate and bulbourethral glands. Male marsupials have 1-3 pairs of bulbourethral glands. There are no ampullae, seminal vesicles or coagulating glands. The prostate is proportionally larger in marsupials than in placental mammals. During the breeding season, the male tammar wallaby's prostate and bulbourethral gland enlarge. However, there does not appear to be any seasonal difference in the weight of the testes.


Female reproductive system

Female marsupials have two lateral vaginas, which lead to separate uteri, but both open externally through the same orifice. A third canal, the median vagina, is used for birth. This canal can be transitory or permanent. Some marsupial species are able to female sperm storage, store sperm in the oviduct after mating. Marsupials give birth at a very early stage of development; after birth, newborn marsupials crawl up the bodies of their mothers and attach themselves to a teat, which is located on the underside of the mother, either inside a pouch called the marsupium, or open to the environment. Mothers often lick their fur to leave a trail of scent for the newborn to follow to increase chances of making it into the marsupium. There they remain for a number of weeks, attached to the teat. The offspring are eventually able to leave the marsupium for short periods, returning to it for warmth, protection, and nourishment.


=Early development

= Prenatal development differs between marsupials and Placentalia, placental mammals. Key aspects of the first stages of placental mammal embryo development, such as the inner cell mass and the process of compaction, are not found in marsupials. The cleavage (embryo), cleavage stages of marsupial development are very variable between groups and aspects of marsupial early development are not yet fully understood. An early birth removes a developing marsupial from its mother's body much sooner than in placental mammals; thus marsupials have not developed a complex placenta to protect the embryo from its mother's immune system. Though early birth puts the tiny newborn marsupial at a greater environmental risk, it significantly reduces the dangers associated with long pregnancies, as there is no need to carry a large fetus to full term in bad seasons. Marsupials are extremely altricial animals, needing to be intensely cared for immediately following birth (cf. precocial). Because newborn marsupials must climb up to their mother's teats, their front limbs and facial structures are much more developed than the rest of their bodies at the time of birth. This requirement has been argued to have resulted in the limited range of locomotor adaptations in marsupials compared to placentals. Marsupials must develop grasping forepaws during their early youth, making the evolutive transition from these limbs into hoof, hooves, wings, or flipper (anatomy), flippers, as some groups of placental mammals have done, more difficult. However, several marsupials do possess atypical forelimb morphologies, such as the hooved forelimbs of the
pig-footed bandicoot ''Chaeropus'', known as the pig-footed bandicoots, is a genus of small mammals that became extinct during the twentieth century. They were unique marsupials Marsupials are any members of the mammal Mammals (from Latin language, Latin , ...

pig-footed bandicoot
, suggesting that the range of forelimb specialization is not as limited as assumed. An infant marsupial is known as a joey. Marsupials have a very short gestation period—usually around four to five weeks, but as low as 12 days for some species—and the joey is born in an essentially Fetus, fetal state. The blind, furless, miniature newborn, the size of a jelly bean, crawls across its mother's fur to make its way into the pouch, where it latches onto a
teat A teat is the projection from the mammary gland A mammary gland is an exocrine gland in humans and other mammals that produces milk to feed young offspring. Mammals get their name from the Latin word ''mamma'', "breast". The mammary glands a ...
for food. It will not re-emerge for several months, during which time it develops fully. After this period, the joey begins to spend increasing lengths of time out of the pouch, feeding and learning survival skills. However, it returns to the pouch to sleep, and if danger threatens, it will seek refuge in its mother's pouch for safety. Joeys stay in the pouch for up to a year in some species, or until the next joey is born. A marsupial joey is unable to regulate its own body temperature and relies upon an external heat source. Until the joey is well furred and old enough to leave the pouch, a pouch temperature of must be constantly maintained. Joeys are born with "oral shields". In species without pouches or with rudimentary pouches these are more developed than in forms with well-developed pouches, implying a role in maintaining the young attached to the mother's teat.


Geography

In Australasia, marsupials are found in Australia, Tasmania and New Guinea; throughout the Maluku Islands, Timor and Sulawesi to the west of New Guinea, and in the Bismarck Archipelago (including the Admiralty Islands) and Solomon Islands to the east of New Guinea. In America, marsupials are found throughout South America, excluding the central/southern Andes and parts of Patagonia; and through Central America and south-central Mexico, with a single species widespread in the eastern United States and along the Pacific coast.


Interaction with Europeans

The first American marsupial (and marsupial in general) that a European encountered was the common opossum. Vicente Yáñez Pinzón, commander of the ''Niña'' on Christopher Columbus' Voyages of Christopher Columbus#First voyage, first voyage in the late 1400s, collected a female opossum with young in her pouch off the South American coast. He presented them to the Spain, Spanish monarchs, though by then the young were lost and the female had died. The animal was noted for its strange pouch or "second belly", and how the offspring reached the pouch was a mystery. On the other hand, it was the Portuguese people, Portuguese who first described Australasian marsupials. António Galvão, a Portuguese administrator in Ternate (1536–40), wrote a detailed account of the northern common cuscus (''Phalanger orientalis''): From the start of the 17th century more accounts of marsupials arrived. For instance, a 1606 record of an animal, killed on the southern coast of New Guinea, described it as "in the shape of a dog, smaller than a greyhound", with a snakelike "bare scaly tail" and hanging testicles. The meat tasted like venison, and the stomach contained ginger leaves. This description appears to closely resemble the dusky pademelon (''Thylogale brunii''), in which case this would be the earliest European record of a member of the kangaroo family (
Macropodidae Macropodidae is a family In , family (from la, familia) is a of people related either by (by recognized birth) or (by marriage or other relationship). The purpose of families is to maintain the well-being of its members and of society ...
).


Evolutionary history

The relationships among the three extant divisions of mammals (
monotreme Monotremes are prototherian mammals of the order Monotremata. They are one of the three main groups of living mammals, along with placentals (Eutheria) and marsupials (Metatheria). Monotremes are typified by structural differences in their brai ...
s, marsupials, and placental mammal, placentals) were long a matter of debate among taxonomy (biology), taxonomists. Most Morphology (biology), morphological evidence comparing traits such as dentition, number and arrangement of teeth and structure of the Genitourinary system, reproductive and waste elimination systems as well as most Molecular genetics, genetic and molecular evidence favors a closer evolutionary relationship between the marsupials and placental mammals than either has with the monotremes. The ancestors of marsupials, part of a larger group called
metatheria Metatheria is a mammalian clade A clade (), also known as a monophyletic group or natural group, is a group of organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All or ...
ns, probably split from those of placental mammals (eutherians) during the mid-Jurassic period, though no fossil evidence of metatherians themselves are known from this time. From DNA and protein analyses, the time of divergence of the two lineages has been estimated to be around 100 to 120 Million years ago, mya. Fossil metatherians are distinguished from eutherians by the form of their teeth; metatherians possess four pairs of molar tooth, molar teeth in each jaw, whereas eutherian mammals (including true placentals) never have more than three pairs. Using this criterion, the earliest known metatherian was thought to be ''Sinodelphys, Sinodelphys szalayi'', which lived in China around 125 mya. However ''Sinodelphys'' was later reinterpreted as an early member of
Eutheria Eutheria (; from Greek , 'good, right' and , 'beast'; ) is the clade consisting of all Theria, therian mammals that are more closely related to Placentalia, placentals than to Marsupial, marsupials. Eutherians are distinguished from noneuther ...

Eutheria
. The unequivocal oldest known metatherians are now 110 million years old fossils from western North America. About 100 mya, the supercontinent Pangaea was in the process of splitting into the northern continent Laurasia and the southern continent
Gondwana Gondwana () or Gondwanaland was a supercontinent In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (ge ...

Gondwana
, with what would become China and Australia already separated by the Tethys Ocean. From there, metatherians spread westward into modern North America (still attached to Eurasia), where the earliest true marsupials are found. Marsupials are difficult to distinguish from other fossils, as they are characterized by aspects of the reproductive system which do not normally fossilize (including pouches) and by subtle changes in the bone and tooth structure that show a metatherian is part of the marsupial crown group (the most exclusive group that contains all living marsupials). The earliest definite marsupial fossil belongs to the species ''Peradectes minor'', from the Paleocene of Montana, dated to about 65 million years ago. From their point of origin in Laurasia, marsupials spread to South America, which was possibly connected to North America at around 65 mya through a ridge that has since moved on to become the Caribbean Archipelago. Laurasian marsupials eventually died off, for not entirely clear reasons; convention has it that they disappeared due to competition with placentals, but this is no longer accepted to be the primary reason. Marsupials, ''Peradectes'' and the related Herpetotheriidae are nested within a clade of metatherians that also included a variety of Cretaceous North American taxa. In South America, the Didelphimorphia, opossums evolved and developed a strong presence, and the Paleogene also saw the evolution of
shrew opossum The family In human society, family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of families is to maintain the well-being of i ...
s (Paucituberculata) alongside non-marsupial metatherian predators such as the borhyaenidae, borhyaenids and the saber-toothed ''Thylacosmilus''. South American niches for mammalian carnivores were dominated by these marsupial and sparassodonta, sparassodont metatherians, which seem to have competitive exclusion, competitively excluded South American placentals from evolving carnivory. While placental predators were absent, the metatherians did have to contend with avian (Phorusrhacidae, terror bird) and terrestrial crocodylomorph competition. Marsupials were excluded in turn from large herbivore niches in South America by the presence of native placental Meridiungulata, ungulates (now extinct) and xenarthrans (whose largest forms are also extinct). South America and Antarctica remained connected until 35 mya, as shown by the unique fossils found there. North and South America were disconnected until about three million years ago, when the Isthmus of Panama formed. This led to the Great American Interchange. Sparassodonts disappeared for unclear reasons – again, this has classically assumed as competition from carnivoran placentals, but the last sparassodonts co-existed with a few small carnivorans like Procyonidae, procyonids and canines, and disappeared long before the arrival of macropredatory forms like felines, while didelphimorphs (opossums) invaded Central America, with the
Virginia opossum The Virginia opossum (''Didelphis virginiana''), commonly known as the North American opossum, is the only opossum The opossum ( or ) is a marsupial of the Order (biology), order Didelphimorphia () Endemism, endemic to the Americas. The larges ...
reaching as far north as Canada. Marsupials reached Australia via Antarctica about 50 mya, shortly after Australia had split off. This suggests a single dispersion event of just one species, most likely a relative to South America's
monito del monte The monito del monte or colocolo opossum, ''Dromiciops gliroides'', also called ''chumaihuén'' in Mapudungun, is a diminutive marsupial native only to southwestern South America South America is a continent entirely in the Western Hemi ...
(a Microbiotheria, microbiothere, the only New World australidelphian). This progenitor may have Oceanic dispersal, rafted across the widening, but still narrow, gap between Australia and Antarctica. The journey must not have been easy; South American ungulate and xenarthran remains have been found in Antarctica, but these groups did not reach Australia. In Australia, marsupials radiated into the wide variety seen today, including not only omnivorous and carnivorous forms such as were present in South America, but also into large herbivores. Modern marsupials appear to have reached the islands of
New Guinea New Guinea (; Hiri Motu Hiri Motu, also known as Police Motu, Pidgin Motu, or just Hiri, is a language A language is a structured system of communication used by humans, including speech (spoken language), gestures (Signed language, sign ...

New Guinea
and Sulawesi relatively recently via Australia. A 2010 analysis of retroposon Retrotransposon marker, insertion sites in the nuclear DNA of a variety of marsupials has confirmed all living marsupials have South American ancestors. The branching sequence of marsupial orders indicated by the study puts Didelphimorphia in the most Basal (phylogenetics), basal position, followed by Paucituberculata, then Microbiotheria, and ending with the radiation of Australian marsupials. This indicates that Australidelphia arose in South America, and reached Australia after Microbiotheria split off. In Australia, terrestrial placental mammals disappeared early in the Cenozoic (their most recent known fossils being 55 million-year-old teeth resembling those of condylarths) for reasons that are not clear, allowing marsupials to dominate the Australian ecosystem. Extant native Australian terrestrial placental mammals (such as hopping mouse, hopping mice) are relatively recent immigrants, arriving via island hopping from Southeast Asia. Genetic analysis suggests a divergence date between the marsupials and the placentals at .Graves JA, Renfree MB (201
Marsupials in the age of genomics
''Annu Rev Genom Hum Genet''
The ancestral number of chromosomes has been estimated to be 2n = 14. A new hypothesis suggests that South American microbiotheres resulted from a back-dispersal from eastern Gondwana due to new cranial and post-cranial marsupial fossils from the ''Djarthia murgonensis'' from the early Eocene Tingamarra Local Fauna in Australia that indicate the ''Djarthia murgonensis'' is the most plesiomorphic, the oldest unequivocal australidelphian, and may be the ancestral morphotype of the Australian marsupial radiation.


See also

* Marsupial lawn * Metatheria


Notes


References


Further reading

* * * * * * * Frith, H. J. and J. H. Calaby. Kangaroos. New York: Humanities Press, 1969. * * Hunsaker, Don. The Biology of Marsupials. New York: Academic Press, 1977. * * * * * *


External links

* *
First marsupial genome released. Most differences between the opossom and placental mammals stem from non-coding DNA
{{Authority control Extant Paleocene first appearances Marsupials,