Marsupials are any members of the mammalian infraclass Marsupialia.
All extant marsupials are endemic to
Australasia and the Americas. A
distinctive characteristic common to these species is that most of the
young are carried in a pouch. Well-known marsupials include kangaroos,
wallabies, koalas, possums, opossums, wombats, and Tasmanian devils.
Some lesser-known marsupials are the potoroo and the quokka.
Marsupials represent the clade originating from the last common
ancestor of extant metatherians. Like other mammals in the Metatheria,
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 species occur on the Australian
continent (the mainland, Tasmania,
New Guinea and nearby islands). The
remaining 100 are found in the
Americas — primarily in South
America, but thirteen in Central America, and one 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 μάρσιππος, which means "pouch."
2.1.1 Skull and teeth
2.1.3 General and convergences
2.2 Reproductive system
2.2.1 Male reproductive system
2.2.2 Female reproductive system
18.104.22.168 Early development
4 See also
7 Further reading
8 External links
Taxonomically, the two primary divisions of Marsupialia are American
marsupials (Ameridelphia) and Australian marsupials
(Australidelphia). The order
Microbiotheria (which has only one
species, the monito del monte) is found in South America, but is
believed to be more closely related to Australian marsupials. DNA
evidence supports a South American origin for marsupials, with
Australian marsupials arising from a single Gondwanan migration of
South America to Australia. There are many small
arboreal species in each group. The term "opossum" is used to refer to
American species (though "possum" is a common diminutive), while
similar Australian species are properly called "possums".
Didelphimorphia (93 species)
Family Didelphidae: opossums
Paucituberculata (seven species)
Family Caenolestidae: shrew opossums
Microbiotheria (one species)
Family Microbiotheriidae: monito del monte
Yalkaparidontia (incertae sedis)
Dasyuromorphia (75 species)
Family †Thylacinidae: thylacine
Family Dasyuridae: antechinuses, quolls, dunnarts, Tasmanian devil,
Family Myrmecobiidae: numbat
Notoryctemorphia (two species)
Family Notoryctidae: marsupial moles
Peramelemorphia (24 species)
Family Thylacomyidae: bilbies
Family †Chaeropodidae: pig-footed bandicoot
Family Peramelidae: bandicoots and allies
Diprotodontia (137 species)
Family Phascolarctidae: koalas
Family Vombatidae: wombats
Family †Diprotodontidae: diprotodon
Family Phalangeridae: brushtail possums and cuscuses
Family Burramyidae: pygmy possums
Family Tarsipedidae: honey possum
Family Petauridae: striped possum, Leadbeater's possum, yellow-bellied
glider, sugar glider, mahogany glider, squirrel glider
Family Pseudocheiridae: ringtailed possums and relatives
Family Potoroidae: potoroos, rat kangaroos, bettongs
Family Acrobatidae: feathertail glider and feather-tailed possum
Family Hypsiprymnodontidae: musky rat-kangaroo
Family Macropodidae: kangaroos, wallabies, and relatives
Family †Thylacoleonidae: marsupial lions
Cladogram based on Gallus, S. et al. (2015)
Marsupials have the typical characteristics of mammals—e.g., mammary
glands, three middle ear bones, and true hair. There are, however,
striking differences as well as a number of anatomical features that
separate them from Eutherians.
In addition to the front pouch, which contains multiple nipples for
the protection and sustenance of their young, marsupials have other
common structural features. Ossified patellae are absent in most
modern marsupials (though a small number of exceptions are
reported) and epipubic bones are present. Marsupials (and
monotremes) also lack a gross communication (corpus callosum) between
the right and left brain hemispheres.
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Skull and teeth
The skull has peculiarities in comparison to higher 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 further 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 higher
mammals' foramina, always have more openings. The teeth differ from
that of placental mammals, so that all taxa except wombats have a
different number of incisors in the upper and lower jaws. The early
marsupials had a dental formula from 5 / 4-1 / 1-3 / 3-4 / 4, that is,
per pine half; they have five maxilla or four mandibular incisors, one
canine, three premolars and four molars, for a total of 50 teeth. Some
taxa, such as the opossum, have the original number of teeth. In other
groups the number of teeth is reduced. Marsupials in many cases have
40 to 50 teeth, significantly more than placental mammals. The upper
jaw has a high number of incisors, up to ten, and they have more
molars than premolars. The second set of teeth grows in only at the
3rd premolar: all remaining teeth are already created as permanent
Few general characteristics describe their skeleton. In addition to
details in the construction of the ankle, bones (Ossa epubica) are
characteristic, two from the pubic bone of the pelvis, which is a
forwardly projecting bone. 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. The egg-laying platypus have marsupial
bones. This could be explained by an original feature of mammals.
Marsupial reproductive organs differ from the higher 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 some but not all species. Some marsupials have a
permanent bag, whereas in others the pouch develops during gestation,
as with the shrew opossum, 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 has a
pouch that is used to accommodate his genitalia while swimming or
General and convergences
The sugar glider, a marsupial, (left) and flying squirrel, a rodent,
(right) are examples of convergent evolution.
Marsupials have adapted to many habitats, reflected in the wide
variety in their build. The largest living marsupial, the red
kangaroo, grows up to 1.8 metres (5.9 ft) in height and 90
kilograms (200 lb) in weight, but extinct genera, such as
Diprotodon, were significantly larger and heavier. The smallest
members of this group are the marsupial mice, which often reach only 5
centimetres (2.0 in) in body length.
Some species resemble higher mammals and are examples of convergent
evolution. The extinct
Thylacine strongly resembled the placental
wolf, hence its nickname "Tasmanian wolf". Flying and the associated
ability to glide occurred both with marsupials (as with sugar gliders)
and some higher mammals (as with flying squirrels), which developed
independently. Other groups such as the kangaroo, however, do not have
Kangaroo § Reproduction and life cycle
Female eastern grey kangaroo with a joey in her pouch
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 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 macropods and marsupial
moles, 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, 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
The male thylacine had a pouch that acted as a protective sheath,
covering his external reproductive organs while he ran through thick
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
The only accessory sex glands marsupials possess are the prostate and
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
See also: Birth § Marsupials
Female reproductive anatomy of several marsupial species
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.
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 nipple, which is located on the underside of
the mother, either inside a pouch called the marsupium, or open to the
environment. There they remain for a number of weeks, attached to the
nipple. The offspring are eventually able to leave the marsupium for
short periods, returning to it for warmth, protection, and
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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
Because newborn marsupials must climb up to their mother's nipples,
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 hooves, wings, or 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, suggesting
that the range of forelimb specialization is not as limited as
An infant marsupial is known as a joey. Marsupials have a very short
gestation period (about four to five weeks), and the joey is born in
an essentially 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 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
30–32 °C (86–90 °F) 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 nipple.
See also: Evolution of mammals
Isolated petrosals of Djarthia murgonensis, Australia's oldest
Dentition of the herbivorous eastern grey kangaroo, as illustrated in
Knight's Sketches in Natural History
The relationships among the three extant divisions of mammals
(monotremes, marsupials, and placentals) were long a matter of debate
among taxonomists. Most morphological evidence comparing traits
such as number and arrangement of teeth and structure of the
reproductive and waste elimination systems as well as most genetic and
molecular evidence favors a closer evolutionary relationship between
the marsupials and placental mammals than either has with the
Phylogenetic tree of marsupials derived from retroposon data
The ancestors of marsupials, part of a larger group called
metatherians, 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. Fossil
metatherians are distinguished from eutherians by the form of their
teeth; metatherians possess four pairs of molar teeth in each jaw,
whereas eutherian mammals (including true placentals) never have more
than three pairs. Using this criterion, the earliest known
Sinodelphys szalayi, which lived in China around 125
million years ago (mya). This makes it a contemporary to some
early eutherian species which have been found in the same area.
The oldest metatherian fossils are found in present-day China.
About 100 mya, the supercontinent
Pangaea was in the process of
splitting into the northern continent
Laurasia and the southern
continent 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,
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
Marsurpials, Peradectes and the related
Herpetotheriidae are nested
within a clade of metatherians that also included a variety of
Cretaceous North American taxa.
Gurlin Tsav skull
In South America, the opossums evolved and developed a strong
presence, and the
Paleogene also saw the evolution of shrew opossums
(Paucituberculata) alongside non-marsupial metatherian predators such
as the borhyaenids and the saber-toothed Thylacosmilus. South American
niches for mammalian carnivores were dominated by these marsupial and
sparassodont metatherians. While placental predators were absent, the
metatherians did have to contend with avian (terror bird) and
terrestrial crocodylomorph competition.
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
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 procyonids and canines, and disappeared
long before the arrival of macropredatory forms like felines,
while didelphimorphs (opossums) invaded Central America, with the
Virginia opossum 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 (a microbiothere, the only New World australidelphian). This
progenitor may have rafted across the widening, but still narrow, gap
between Australia and Antarctica. In Australia, they radiated into the
wide variety seen today. Modern marsupials appear to have reached the
New Guinea and
Sulawesi relatively recently via
Australia. A 2010 analysis of retroposon 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 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 mice)
are relatively recent immigrants, arriving via island hopping from
Genetic analysis suggests a divergence date between the marsupials and
the placentals at 160 million years ago. 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
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.
Geological time scale of marsupial evolution
10,000 ya – present
First Europeans visit Australia in 1606, settlements begin in 1788.
Dingo introduced 3500-4000 ya.
Thylacine and Tasmanian devil
subsequently disappear from Australian mainland.
1.75 Mya – 10,000
Last glacial maximum 18,000–20,000 ya
Extinction of megafauna 45,000–55,000 ya.
First humans arrive in Australia at least 70,000~65,000 ya.
Growing diversity in grazing marsupials as a result of grasslands and
arid habitats development.
First appearance of large marsupials.
Miocene 11–5.3 Mya
'Dim age' of marsupial fossils in Australia. Forest-dwellers diminish.
Miocene 16.4–11 Mya
Icehouse conditions result in the number of forest and forest-dwelling
marsupials to decrease.
Miocene 23.5–16.4 Mya
Greenhouse conditions in Australia result in great diversity of
Oligocene 33–23 Mya
Appearance of marsupials in Australian fossil record
Eocene 53–33.7 Mya
Australia separates from Antarctica.
High marsupial diversity in South America. Appearance of the oldest
Australian marsupial in late Paleocene.
Dinosaurs are wiped off the Earth after an asteroid collision.
Cretaceous 97–65 Mya
The northern landmass, Laurasia, is inhabited by marsupials. Some of
them start dispersing to South America.
Cretaceous 135–97 Mya
First appearance of marsupial and placental fossils.
Jurassic 203–135 Mya
Break apart of the great southern landmass, Gondwana. Marsupials and
Triassic 250–203 Mya
First mammals appear in late
Triassic in the supercontinent, Pangaea.
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Marsupial reproductive system.
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Definitions from Wiktionary
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Learning resources from Wikiversity
Taxonomy from Wikispecies
Researchers Publish First
Marsupial Genome Sequence The National
Institutes of Health May 2007
First marsupial genome released. Most differences between the opossom
and placental mammals stem from non-coding DNA
Extant mammal orders
Platypus and echidnas)
Paucituberculata (Shrew opossums)
Microbiotheria (Monito del monte)
Dasyuromorphia (Quolls and dunnarts)
Peramelemorphia (Bilbies and bandicoots)
Diprotodontia (Kangaroos and relatives)
Pilosa (Anteaters and sloths)
Afrosoricida (Tenrecs and golden moles)
Macroscelidea (Elephant shrews)
Sirenia (Dugongs and manatees)
Eulipotyphla (Hedgehogs, shrews, moles and relatives)
Carnivora (Dogs, cats and relatives)
Perissodactyla (Odd-toed ungulates)
Artiodactyla (Even-toed ungulates and cetaceans)
Lagomorpha (Rabbits and pikas)