Marsupial

This article is about the mammals. For frogs, see Marsupial frog.
Marsupials[1][2]
Temporal range: Paleocene – Holocene, 65–0 Ma
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Synapsida
Class: Mammalia
Clade: Metatheria
Infraclass: Marsupialia
Illiger, 1811
Orders
Present-day distribution of marsupials.

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, Tasmanian devils, and the recently extinct thylacines. Others include the numbat, the bandicoot, the bettong, the bilby, the quoll, 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 with the mother in a pouch, 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.

Taxonomy

Taxonomically, the two primary divisions of Marsupialia are: American and Australian marsupials.[1][2] 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. 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". Again, shrew opossums are more closely related to australidelphians than to true opossums.[3][4]

†Extinct

Marsupialia

Didelphimorphia

Paucituberculata


Australidelphia

Microbiotheria

Diprotodontia

Dasyuromorphia

Notoryctemorphia

Peramelemorphia







Cladogram based on Gallus, S. et al. (2015)[5]

Anatomy

Koala
(Phascolarctos cinereus)

Marsupials have the typical characteristics of mammals—e.g., a fur coat. There are, however, striking differences as well as a number 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.[6]

Description

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 teeth.

Torso

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 pseudo-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 offspring in the scrotum while swimming or running.

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 show resemble higher mammals and are examples of convergent evolution. The extinct Thylacine strongly resembles 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 placental counterparts.

Reproductive system

Female eastern grey kangaroo with a joey in her pouch

Marsupials' reproductive systems differ markedly from those of placental mammals.[7][8] The female develops a kind of yolk sac in her womb which delivers nutrients to the embryo. Embryos of some marsupials additionally form placenta-like organs that connect them to the uterine wall, although it is not certain that they transfer nutrients from the mother to the embryo.[9] Pregnancy is very short, typically 4 to 5 weeks, and the embryo is born at a very young stage of development.

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,[8] 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.[8]

Male reproductive system

Most male marsupials, except for macropods[10] and marsupial moles,[11] have a bifurcated penis, separated into two columns, so that the penis has two ends corresponding to the females' two vaginas.[6][8][12][13][14][15][16][17][18] The penis is used only for inseminating females, and is separate from the urinary tract.[8][19] It curves forward when erect,[20] and when not erect, it is retracted into the body in an S-shaped curve.[14] Neither marsupials nor monotremes possess a baculum.[6] The shape of the glans penis varies among marsupial species.[14][21][22][23] A male koala's foreskin contains naturally occurring bacteria that play an important role in fertilization.[24]

The male thylacine had a pouch that acted as a protective sheath, covering his external reproductive organs while he ran through thick brush.[25]

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.[26] Several species of dasyurid marsupials can also be distinguished by their penis morphology.[27]

The prostate is proportionally larger in marsupials than in placental mammals.[14] 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.[28]

Female reproductive system

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.[6] The definitive placenta in all marsupials is generated by the yolk sac.[29] Among three fetal membranes in mammals, the yolk sac, allantois, and amnion, only the first two form a placenta.[30] The evolution of placentation in vertebrates is linked to the evolution of viviparity, a reproductive system in which the females retain their eggs to give birth to their young. Marsupials give birth at a very early stage of development (about four to five weeks); 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. To crawl to the nipple and attach to it, the marsupial must have well-developed forelimbs and facial structures.[31][32] This is accomplished by accelerating forelimb and facial development in marsupials compared to placental mammals, which results in decelerated development of such structures as the hindlimb and brain. 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 nourishment.

Early development

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 nipples, their front limbs 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 transition from these limbs into hooves, wings, or flippers, as some groups of placental mammals have done, far 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 speciation is a lot less limited than usually assumed.[33]

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,[34] 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.[35]

Evolution

Isolated petrosals of Djarthia murgonensis, Australia's oldest marsupial fossils[36]
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.[37] 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 monotremes.[38]

Phylogenetic tree of marsupials derived from retroposon data[4]

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.[39] 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.[40] Using this criterion, the earliest known metatherian is Sinodelphys szalayi, which lived in China around 125 million years ago (mya).[41] This makes it a contemporary to some early eutherian species which have been found in the same area.[42]

The oldest metatherian fossils are found in present-day China.[43] 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, from the Paleocene of Montana, dated to about 65 million years ago.[44] From their point of origin in Laurasia, marsupials spread to South America, which was connected to North America until around 65 mya. 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.[45]

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 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,[46] 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 islands of Borneo and Sulawesi relatively recently via Australia.[47][48][49] 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.[3][4]

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.[47] Extant native Australian terrestrial placental mammals (such as hopping mice) are relatively recent immigrants, arriving via island hopping from Southeast Asia.[48]

Genetic analysis suggests a divergence date between the marsupials and the placentals at 160 million years ago.[50] 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.[51]

See also

Wikimedia Commons has media related to Marsupial reproductive system.

Notes

    References

    1. 1 2 Gardner, A. (2005). Wilson, D.E.; Reeder, D.M., eds. Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. pp. 3–21. ISBN 978-0-8018-8221-0. OCLC 62265494.
    2. 1 2 Groves, C.P. (2005). Wilson, D.E.; Reeder, D.M., eds. Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Baltimore: Johns Hopkins University Press. pp. 22–70. OCLC 62265494. ISBN 0-801-88221-4.
    3. 1 2 Schiewe, Jessie (2010-07-28). "Australia's marsupials originated in what is now South America, study says". LA Times. Los Angeles Times. Archived from the original on 1 August 2010. Retrieved 2010-08-01.
    4. 1 2 3 Nilsson, M. A.; Churakov, G.; Sommer, M.; Van Tran, N.; Zemann, A.; Brosius, J.; Schmitz, J. (2010). "Tracking Marsupial Evolution Using Archaic Genomic Retroposon Insertions". PLoS Biology. Public Library of Science. 8 (7): e1000436. doi:10.1371/journal.pbio.1000436. PMC 2910653Freely accessible. PMID 20668664.
    5. ↑ Gallus, A. Kumar; Janke, S.; Nilsson, M.A. (2015). "Disentangling the relationship of the Australian marsupial orders using retrotransposon and evolutionary network analyses". Genome Biol Evol. 7 (4): 985–92. doi:10.1093/gbe/evv052. PMC 4419798Freely accessible. PMID 25786431.
    6. 1 2 3 4 Nowak, Ronald M. (1999). Walker's Mammals of the World. Johns Hopkins University Press. ISBN 9780801857898.
    7. ↑ Short, R. V.; Balaban, E. (1994). The Differences Between the Sexes. Cambridge University Press. ISBN 978-0-521-44878-9.
    8. 1 2 3 4 5 King, Anna (2001). "Discoveries about Marsupial Reproduction". Iowa State University Biology Dept. Retrieved 2012-11-22.
    9. ↑ "Family Peramelidae (bandicoots and echymiperas)".
    10. ↑ Lynda Staker (30 June 2014). Macropod Husbandry, Healthcare and Medicinals—Volumes One and Two. Lynda Staker. ISBN 978-0-9775751-2-1.
    11. ↑ On the Habits and Affinities of the New Australian Mammal, Notoryctes typhlops E. D. Cope The American Naturalist Vol. 26, No. 302 (Feb., 1892), pp. 121-128
    12. ↑ Don II Hunsaker (1977). The Biology of Marsupials. Elsevier Science. ISBN 978-0-323-14620-3.
    13. ↑ Biggers, J. D. "Reproduction in male marsupials." Comparative biology of reproduction in mammals (IW Rowlands, ed.). Academic Press, New York (1966): 251–280.
    14. 1 2 3 4 Renfree, Marilyn; Hugh Tyndale-Biscoe (1987). Reproductive Physiology of Marsupials. Cambridge University Press. ISBN 9780521337922.
    15. ↑ Rodger, JC; Hughes, RL (1973). "Studies of the accessory glands of male marsupials". Australian Journal of Zoology. 21 (3): 303. doi:10.1071/ZO9730303.
    16. ↑ Sharman, G. B.; Pilton, Phyllis E. (1964). "The life history and reproduction of the red kangaroo (Megaleia rufa)". Proceedings of the Zoological Society of London. 142 (1): 29–48. doi:10.1111/j.1469-7998.1964.tb05152.x.
    17. ↑ Sadleir, R. M. F. S. (1965). "Reproduction in two species of kangaroo (Macropus robustus and Megaleia rufa in the arid Pilbara region of Western Australia". Proceedings of the Zoological Society of London. 145 (2): 239–261. doi:10.1111/j.1469-7998.1965.tb02016.x.
    18. ↑ "Sexual Reproduction and Development". University of Bristol. Retrieved 2015-02-19.
    19. ↑ Vogelnest, Larry; Woods, Rupert (2008). Medicine of Australian Mammals. Csiro Publishing. ISBN 978-0-643-09928-9.
    20. ↑ Sadleir, Richard (1973). The Reproduction of Vertebrates. Elsevier Science. ISBN 978-0-323-15935-7.
    21. ↑ Australian Mammal Society (1978). Australian Mammal Society. Australian Mammal Society. pp. 73–.
    22. ↑ Osgood, Wilfred Hudson; Herrick, Charles Judson (1921). A monographic study of the American marsupial, Caēnolestes ... University of Chicago. pp. 64–.
    23. ↑ The Urologic and Cutaneous Review. Urologic & Cutaneous Press. 1920. pp. 677–.
    24. ↑ "UQ researchers unlock another koala secret". Uq.edu.au. 2001-05-09. Retrieved 2012-07-16.
    25. ↑ Paddle, Robert (2002). The last Tasmanian tiger : the history and extinction of the thylacine (Paperback ed.). Port Melbourne, Vic.: Cambridge University Press. ISBN 978-0-521-53154-2.
    26. ↑ Nogueira, J., Castro, A. S., Câamara, E. C., & Câmara, B. O. (2004). "Morphology of the Male Genital system of Chironectes minimus and Comparison to other didelphid marsupials". Journal of Mammalogy. 85 (5): 834–841. doi:10.1644/207.
    27. ↑ Woolley, Patricia A., Michael Westerman, and Carey Krajewski. "Interspecific affinities within the genus Sminthopsis (Dasyuromorphia: Dasyuridae) based on morphology of the penis: congruence with other anatomical and molecular data." Journal of Mammalogy 88.6 (2007): 1381-1392.
    28. ↑ Inns, R. W. (1982). "Seasonal changes in the accessory reproductive system and plasma testosterone levels of the male tammar wallaby, Macropus eugenii, in the wild". Journal of Reproduction and Fertility. 66 (2): 675–80. doi:10.1530/jrf.0.0660675. PMID 7175821.
    29. ↑ Luckett, W.P. "Ontogeny of amniote fetal membranes and their application to phylogeny". Major Patterns in Vertebrate Evolution. New York, London: Plenum Publishing Corporation. pp. 439–516. doi:10.1007/978-1-4684-8851-7_16. ISBN 978-1-4684-8851-7.
    30. ↑ Freyer, Claudia; Renfree, Marilyn B. (2009). "The mammalian yolk sac placenta". Journal of Experimental Zoology Part B: Molecular and Developmental Evolution. 312B (6): 545–554. doi:10.1002/jez.b.21239.
    31. ↑ Sears, K. E. (2009). "Differences in the Timing of Prechondrogenic Limb Development in Mammals: The Marsupial-Placental Dichotomy Resolved". Evolution. 63 (8): 2193–2200. doi:10.1111/j.1558-5646.2009.00690.x. PMID 19453378.
    32. ↑ Smith, K. K. (2001). "Early development of the neural plate, neural crest and facial region of marsupials". Journal of Anatomy. 199 (Pt 1–2): 121–131. doi:10.1046/j.1469-7580.2001.19910121.x. PMC 1594995Freely accessible. PMID 11523813.
    33. ↑ Larry Vogelnest,Graeme Allan, Radiology of Australian Mammals
    34. ↑ http://www.abc.net.au/science/articles/2013/03/18/3718274.htm. Abc.net.au (2013-03-18). Retrieved on 2015-12-15.
    35. ↑ Schneider, Nanette Yvette (Aug 2011). "The development of the olfactory organs in newly hatched monotremes and neonate marsupials". J Anat. 219 (2): 229–242. doi:10.1111/j.1469-7580.2011.01393.x.
    36. ↑ Beck, Robin M. D.; Godthelp, Henk; Weisbecker, Vera; Archer, Michael; Hand, Suzanne J. (2008). Hawks, John, ed. "Australia's oldest marsupial fossils and their biogeographical implications". PLoS ONE. 3 (3): e1858. doi:10.1371/journal.pone.0001858. PMC 2267999Freely accessible. PMID 18365013.
    37. ↑ Moyal, Ann Mozley (2004). Platypus: The Extraordinary Story of How a Curious Creature Baffled the World. Baltimore: The Johns Hopkins University Press. ISBN 0-8018-8052-1.
    38. ↑ van Rheede, T.; Bastiaans, T.; Boone, D.; Hedges, S.; De Jong, W.; Madsen, O. (2006). "The platypus is in its place: nuclear genes and indels confirm the sister group relation of monotremes and therians". Molecular Biology and Evolution. 23 (3): 587–597. doi:10.1093/molbev/msj064. PMID 16291999.
    39. ↑ Zhe-Xi Luo, Chong-Xi Yuan, Qing-Jin Meng and Qiang Ji (2011). "A Jurassic eutherian mammal and divergence of marsupials and placentals". Nature. 476 (7361): 442–445. doi:10.1038/nature10291. PMID 21866158.
    40. ↑ Benton, Michael J. (1997). Vertebrate Palaeontology. London: Chapman & Hall. p. 306. ISBN 0-412-73810-4.
    41. ↑ Rincon, Paul (2003-12-12). "Oldest Marsupial Ancestor Found, BBC, Dec 2003". BBC News. Retrieved 2010-03-16.
    42. ↑ Hu, Y; Meng, J; Li, C; Wang, Y (2010). "New basal eutherian mammal from the Early Cretaceous Jehol biota, Liaoning, China". Proceedings of the Royal Society B. 277 (1679): 229–236. doi:10.1098/rspb.2009.0203. PMC 2842663Freely accessible. PMID 19419990.
    43. ↑ Luo, Zhe-Xi; Ji, Qiang; Wible, John R.; Yuan, Chong-Xi (2003-12-12). "An early Cretaceous tribosphenic mammal and metatherian evolution". Science. 302 (5652): 1934–1940. doi:10.1126/science.1090718. PMID 14671295.
    44. ↑ O'Leary, Maureen A.; Bloch, Jonathan I.; Flynn, John J.; Gaudin, Timothy J.; Giallombardo, Andres; Giannini, Norberto P.; Goldberg, Suzann L.; Kraatz, Brian P.; Luo, Zhe-Xi; Meng, Jin; Ni, Michael J.; Novacek, Fernando A.; Perini, Zachary S.; Randall, Guillermo; Rougier, Eric J.; Sargis, Mary T.; Silcox, Nancy b.; Simmons, Micelle; Spaulding, Paul M.; Velazco, Marcelo; Weksler, John r.; Wible, Andrea L.; Cirranello, A. L. (8 February 2013). "The Placental Mammal Ancestor and the Post–K-Pg Radiation of Placentals". Science. 339 (6120): 662–667. doi:10.1126/science.1229237. PMID 23393258.
    45. ↑ Sánchez-Villagra, Marcelo (2012). "Why are There Fewer Marsupials than Placentals? On the Relevance of Geography and Physiology to Evolutionary Patterns of Mammalian Diversity and Disparity". Journal of Mammalian Evolution. 20 (4): 279–290. doi:10.1007/s10914-012-9220-3.
    46. ↑ Prevosti, Francisco J.; Forasiepi, Analía; Zimicz, Natalia (2011). "The Evolution of the Cenozoic Terrestrial Mammalian Predator Guild in South America: Competition or Replacement?". Journal of Mammalian Evolution. 20: 3–21. doi:10.1007/s10914-011-9175-9.
    47. 1 2 Dawkins, Richard (2005). The Ancestor's Tale : A Pilgrimage to the Dawn of Evolution. Boston: Mariner Books. ISBN 0-618-61916-X.
    48. 1 2 Hand, Suzanne J.; Long, John; Archer, Michael; Flannery, Timothy Fridtjof (2002). Prehistoric mammals of Australia and New Guinea: one hundred million years of evolution. Baltimore: Johns Hopkins University Press. ISBN 0-8018-7223-5.
    49. ↑ Kemp, T.S. (2005). The origin and evolution of mammals. Oxford [Oxfordshire]: Oxford University Press. ISBN 0-19-850761-5.
    50. ↑ Graves JA, Renfree MB (2013) Marsupials in the age of genomics. Annu Rev Genomics Hum Genet
    51. ↑ Beck, Robin M. D.; Godthelp, Henk; Weisbecker, Vera; Archer, Michael; Hand, Suzanne J. (2008). "Australia's Oldest Marsupial Fossils and their Biogeographical Implications". PLoS ONE. 3 (3): e1858. doi:10.1371/journal.pone.0001858. PMC 2267999Freely accessible. PMID 18365013.

    Further reading

    External links

    This article is issued from Wikipedia - version of the 11/14/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.