Marsupials

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?Marsupials Fossil range: Template:Fossil range
Female Eastern Grey Kangaroo with a joey in her pouch Female Eastern Grey Kangaroo with a joey in her pouch
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Mammalia Subclass: Theria Infraclass: Marsupialia Illiger, 1811
Orders
Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia †Sparassodonta †Yalkaparidontia

Marsupials are an infraclass of mammals, characterized by a distinctive pouch (called the marsupium), in which females carry their young through early infancy.

History

It was once commonly believed that marsupials were a primitive forerunner of modern placental mammals, but fossil evidence, first presented by researcher M.J. Spechtt in 1982, conflicts with this assumption^{[How to reference and link to summary or text]}. Instead, both main branches of the mammal tree appear to have evolved concurrently toward the end of the Mesozoic era. In the absence of soft tissues, such as the pouch and reproductive system, fossil marsupials can be distinguished from placentals by the form of their teeth; primitive marsupials possess four pairs of molar teeth in each jaw, whereas placental mammals never have more than three pairs.

Using this criterion, the earliest known marsupial is Sinodelphys szalayi, which lived in China around 125 million years ago. This makes it almost contemporary to the earliest placental fossils, which have been found in the same area.

Some scientists believe that the marsupials evolved in North America and dispersed from there, via Europe, to [Asia and [Africa. This diaspora would have also reached South America before it became an island continent. This theory suggests that marsupials passed from South America through Antarctica to Australia (via Gondwanan land connections), a continent already occupied by placental mammals. Alternatively, another theory posits that marsupials originated in Australia and traveled, via Antarctica and South America, to North America.

The discovery of Chinese marsupials appears to support the idea that marsupials reached Australia via Southeast Asia. However, marsupial fossils found in New Guinea are younger than those in Australia, evidence which presents a problem for this theory. There are a few species of marsupials still living in Asia, especially in the Sulawesi region of Indonesia. These marsupials coexist with primates, hooved mammals and other placentals.^{[How to reference and link to summary or text]}

On most continents, placental mammals were much more successful and no marsupials survived, though in South America the opossums retained a strong presence, and the Tertiary saw the genesis of marsupial predators such as the borhyaenids and the saber-toothed Thylacosmilus. In Australia, however, marsupials displaced placental mammals entirely, and have since dominated the Australian ecosystem. Marsupial success over placental mammals in Australia has been attributed to their comparatively low metabolic rate, a trait which would prove helpful in the hot Australian climate.^{[How to reference and link to summary or text]} As a result, native Australian placental mammals (such as hopping mice) are more recent immigrants.

Description

An early birth removes a developing marsupial from its parent's body much sooner than in placental mammals, and thus marsupials have not developed a complex placenta to protect the embryo from its mother's immune system. Though early birth places 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.

Because newborn marsupials must climb up to their mother's nipples, their front limbs are much more developed than the rest of the body at the time of birth. It is possible that this requirement has resulted in the limited range of locomotor adaptations in marsupials compared to placentals. Marsupials must develop a grasping forepaw during their early youth, making the transition from this limb into a hoof, wing, or flipper, as some groups of placental mammals have done, far more difficult.

There are about 334 species of marsupial, and over 200 are native to Australia and neighboring northern islands. There are also 100 extant American species; these are centered mostly in South America, but the Great American Interchange has provided Central America with 13 species, and North America with one (the Virginia Opossum).

A feature of marsupials (and also monotremes) is the claim they don't have a gross communication (corpus callosum) between the right and left brain hemisphere.^{[How to reference and link to summary or text]}

Reproductive system

Marsupials' reproductive systems differ markedly from those of their placental mammal cousins (Placentalia). Females have two vaginas, both of which open externally through one orifice but lead to different compartments within the uterus. Males generally have a two-pronged penis, which corresponds to the females' two vaginae. The penis is used only for discharging semen into females, and is separate from the urinary tract.^{[How to reference and link to summary or text]} Both sexes possess a cloaca, which is connected to a urogenital sac used to store waste before expulsion.

Pregnant females develop a kind of yolk sac in their wombs, which delivers nutrients to the embryo. Marsupials give birth at a very early stage of development (about 4–5 weeks); after birth, newborn marsupials crawl up the bodies of their mothers and attach themselves to a nipple, which is located inside the marsupium. 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 and nourishment.

Taxonomy

Taxonomically, there are two primary divisions of Marsupialia: American marsupials and the Australian marsupials. 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 the Australian marsupials. There are many small arboreal species in each group. The term opossums is properly used to refer to the American species (though possum is a common diminutive), while similar Australian species are properly called possums.

File:Koala climbing tree.jpg

The Koala (Phascolarctos cinereus)

File:Brushtail possum.jpg

The Common Brushtail Possum (Trichosurus vulpecula)

File:Sugar-Glider-at-Lone-Pine.jpg

The Sugar Glider (Petaurus breviceps)

File:Possum122708.JPG

The Virginia Opossum (Didelphis virginiana), the only North American marsupial

• Superorder Ameridelphia
  • Order Didelphimorphia (93 species)
    • Family Didelphidae: opossums
  • Order Paucituberculata (6 species)
    • Family Caenolestidae: shrew opossums
• Superorder Australidelphia
  • Order †Yalkaparidontia
  • Order Microbiotheria (1 species)
    • Family Microbiotheriidae: Monito del Monte
  • Order Dasyuromorphia (71 species)
    • Family †Thylacinidae: Thylacine
    • Family Dasyuridae: antechinuses, quolls, dunnarts, Tasmanian Devil, and relatives
    • Family Myrmecobiidae: Numbat
  • Order Peramelemorphia (24 species)
    • Family Thylacomyidae: bilbies
    • Family †Chaeropodidae: Pig-footed Bandicoot
    • Family Peramelidae: bandicoots and allies
  • Order Notoryctemorphia (2 species)
    • Family Notoryctidae: marsupial moles
  • Order Diprotodontia (137 species)
    • Family Phascolarctidae: Koala
    • 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 Potoridae: 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
  • Order †Sparassodonta

† indicates extinction

See also

• Kangaroos
• Metatheria
• Opposums

References

• Tim Flannery (1994),The Future Eaters: An Ecological History of the Australasian Lands and People, pages 67–75. ISBN 0-8021-3943-4 ISBN 0-7301-0422-2
• Tim Flannery, Country: a continent, a scientist & a kangaroo, pages 196–200. ISBN 1-920885-76-5
• Austin, C.R. ed. Reproduction in Mammals. Melbourne: Cambridge University Press,1982.
• Bronson, F. H. Mammalian Reproductive Biology. Chicago: University of Chicago Press, 1989.
• Dawson, Terrence J. Kangaroos: Biology of Largest Marsupials. New York: Cornell University Press, 1995.
• Frith, H. J. and J. H. Calaby. Kangaroos. New York: Humanities Press, 1969.
• Gould, Edwin and George McKay. Encyclopedia of Mammals. San Diego: Academic Press, 1998.
• Hunsaker, Don. The Biology of Marsupials. New York: Academic Press, 1977.
• Johnson, Martin H. and Barry J. Everitt. Essential Reproduction. Boston: Blackwell Scientific Publications, 1984.
• Knobill, Ernst and Jimmy D. Neill ed. Encyclopedia of Reproduction. V. 3 New York: Academic Press, 1998
• McCullough, Dale R. and Yvette McCullough. Kangaroos in Outback Australia: Comparative Ecology and Behavior of Three Coexisting Species. New York: Columbia University Press, 2000.
• Taylor, Andrea C. and Paul Sunnucks. Sex of Pouch Young Related to Maternal Weight in Macropus eugeni and M. parma. Australian Journal of Zoology 1997 V. 45 pp. 573–578

Further reading

Papers

• Arrese, C. A., Hart, N. S., Thomas, N., Beazley, L. D., & Shand, J. (2002). Trichromacy in Australian marsupials: Current Biology Vol 12(8) Apr 2002, 657-660.
• Ashwell, K. W. S. (2008). Encephalization of Australian and New Guinean marsupials: Brain, Behavior and Evolution Vol 71(3) Apr 2008, 181-199.
• Ashwell, K. W. S., Marotte, L. R., & Cheng, G. (2008). Development of the olfactory system in a wallaby (Macropus eugenii): Brain, Behavior and Evolution Vol 71(3) Apr 2008, 216-230.
• Ashwell, K. W. S., McAllan, B. M., Mai, J. K., & Paxinos, G. (2008). Cortical cyto- and chemoarchitecture in three small Australian marsupial carnivores: Sminthopsis macroura, Antechinus stuartii and Phascogale calura: Brain, Behavior and Evolution Vol 72(3) 2008, 215-232.
• Blumstein, D. T., Daniel, J. C., & Springett, B. P. (2004). A Test of the Multi-Predator Hypothesis: Rapid Loss of Antipredator Behavior after 130 years of Isolation: Ethology Vol 110(11) Nov 2004, 919-934.
• Bonney, K. R., & Wynne, C. D. L. (2004). Studies of learning and problem solving in two species of Australian marsupials: Neuroscience & Biobehavioral Reviews Vol 28(6) Oct 2004, 583-594.
• Crassini, B. (1999). Editorial: Australian Journal of Psychology Vol 51(2) Aug 1999, ii.
• Doody, J. S., Sims, R. A., & Letnic, M. (2007). Environmental Manipulation to Avoid a Unique Predator: Drinking Hole Excavation in the Agile Wallaby, Macropus agilis: Ethology Vol 113(2) Feb 2007, 128-136.
• Fisher, D. O., Double, M. C., & Moore, B. D. (2006). Number of mates and timing of mating affect offspring growth in the small marsupial Antechinus agilis: Animal Behaviour Vol 71(2) Feb 2006, 289-297.
• Griffin, A. S., & Evans, C. S. (2003). The role of differential reinforcement in predator avoidance learning: Behavioural Processes Vol 61(1-2) Feb 2003, 87-94.
• Griffin, A. S., Evans, C. S., & Blumstein, D. T. (2002). Selective Learning in a Marsupial: Ethology Vol 108(12) Dec 2002, 1103-1114.
• Harman, A., Meyer, P., & Ahmat, A. (2003). Neurogenesis in the hippocampus of an adult marsupial: Brain, Behavior and Evolution Vol 62(1) Aug 2003, 1-12.
• Hope, P. J., Turnbull, H., Farr, S., Morley, J. E., Rice, K. C., Chrousos, G. P., et al. (2000). Peripheral administration of CRF and urocortin: Effects on food intake and the HPA axis in the marsupial Sminthopsis crassicaudata: Peptides Vol 21(5) May 2000, 669-677.
• Jones, M. E. (1998). The function of vigilance in sympatric marsupial carnivores: The eastern quoll and the Tasmanian devil: Animal Behaviour Vol 56(5) Nov 1998, 1279-1284.
• Mark, R. F., Flett, D. L., Marotte, L. R., & Waite, P. M. E. (2002). Developmental onset of functional activity in the wallaby whisker cortex in response to stimulation of the infraorbital nerve: Somatosensory & Motor Research Vol 19(3) 2002, 198-206.
• McAllan, B. M., Westman, W., Kortner, G., & Cairns, S. C. (2008). Sex, season and melatonin administration affects daily activity rhythms in a marsupial, the brown antechinus, Antechinus stuartii: Physiology & Behavior Vol 93(1-2) Jan 2008, 130-138.
• McCluskey, S. U., Marotte, L. R., & Ashwell, K. W. S. (2008). Development of the vestibular apparatus and central vestibular connections in a wallaby (Macropus eugenii): Brain, Behavior and Evolution Vol 71(4) May 2008, 271-286.
• Mechkour, F., Maublanc, M.-L., Bideau, E., Gerard, J.-F., & Pepin, D. (2008). Spatial organization and spatial distribution of activities within home ranges in a springbok (Antidorcas marsupialis) captive population: Zoo Biology Vol 27(1) Jan-Feb 2008, 19-35.
• Nelson, J., & Gemmell, R. (2004). Implications of Marsupial Births for an Understanding of Behavioural Development: International Journal of Comparative Psychology Vol 17(1) 2004, 53-70.
• Ng, K.-L., Vozzo, R., Hope, P. J., Chapman, I. M., Morley, J. E., Horowitz, M., et al. (1999). Effect of dietary macronutrients on food intake, body weight, and tail width in the marsupial S. crassicaudata: Physiology & Behavior Vol 66(1) Mar 1999, 131-136.
• Radford, S. L., Croft, D. B., & Moss, G. L. (1998). Mate choice in female red-necked pademelons, Thylogale thetis (Marsupialia: macropodidea): Ethology Vol 104(3) Mar 1998, 217-231.
• Rocha-Rego, V., Canteras, N. S., Anomal, R. F., Volchan, E., & Franca, J. G. (2008). Architectonic subdivisions of the amygdalar complex of a primitive marsupial (Didelphis aurita): Brain Research Bulletin Vol 76(1-2) May 2008, 26-35.
• Searle, K. R., Stokes, C. J., & Gordon, I. J. (2008). When foraging and fear meet: Using foraging hierarchies to inform assessments of landscapes of fear: Behavioral Ecology Vol 19(3) May-Jun 2008, 475-482.
• Smith, T., MacFadyen, A., & Rose, R. (2001). Hormonal control of birth behavior in the bandicoot (Perameles gunnii: Marsupialia) and other marsupials: Physiology & Behavior Vol 72(4) Mar 2001, 527-532.
• Spencer, P. B. S., Horsup, A. B., & Marsh, H. D. (1998). Enhancement of reproductive success through mate choice in a social rock-wallaby, Petrogale assimilis (Macropodidae) as revealed by microsatellite markers: Behavioral Ecology and Sociobiology Vol 43(1) Jul 1998, 1-9.
• Strachan, J., Chang, L.-Y. E., Wakefield, M. J., Graves, J. A. M., & Deeb, S. S. (2004). Cone visual pigments of the Australian marsupials, the stripe-faced and fat-tailed dunnarts: Sequence and inferred spectral properties: Visual Neuroscience Vol 21(3) May-Jun 2004, 223-229.
• Wakefield, M. J., Anderson, M., Chang, E., Wei, K.-J., Kaul, R., Graves, J. A. M., et al. (2008). Cone visual pigments of monotremes: Filling the phylogenetic gap: Visual Neuroscience Vol 25(3) May-Jun 2008, 257-264.
• Wittert, G. A., Turnbull, H., & Hope, P. (2005). Exogenously administered leptin leads to weight loss and increased physical activity in the marsupial Sminthopsis crassicaudata: Physiology & Behavior Vol 85(5) Aug 2005, 613-620.
• Wynne, C. D. L., & McLean, I. G. (1999). The comparative psychology of marsupials: Australian Journal of Psychology Vol 51(2) Aug 1999, 111-116.

Dissertations

• Frost, S. B. (1995). The anatomical connections of the non-cortically and cortically projecting medial geniculate body in a neurologically primitive mammal, monodelphis domestica. Dissertation Abstracts International: Section B: The Sciences and Engineering.
• Kahn, D. M. (2002). Organization and connections of the visual system of the metatherian marsupial mammal, monodelphis domestica. Dissertation Abstracts International: Section B: The Sciences and Engineering.

External links

• The Marsupial Ring
• Western Australian Mammal Species
• 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

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