Evolution of the Marsupials Biology 11 Mr. Hill By Beth Connell, Michelle Brouwer, Chase Gaudette, Brendan Martel, and Kaysie Collins

What is A Marsupial? Marsupials (Marsupialia) are particular types of mammals that lives primarily in Australasia and the Americas. The most common characteristic of these mammals are their distinct pouch used for carrying the young. Well-known marsupials include kangaroos, wallabies, the koala, possums, opossums, wombats and the Tasmanian devil. Other marsupials include the numbat, bandicoots, bettongs, the bilby, quolls, and the quokka.

Characteristics Marsupials are best characterized by giving birth to underdeveloped young, because of their short gestation periods. Pregnancies only last about 4-5 weeks. They don’t have a complex enough placenta in order to protect the embryo from its mothers immune system. Which is why they have a front pouch containing essentials such as for breast feeding. Once fully developed (as a baby marsupial) , the newborn can leave the pouch for short periods of time, but must return for nourishments and warmth, usually not after about 7 months. Since the newborn must climb to the pouch at a young age, it develops front limbs long before the rest of the body develops. Because of this, young marsupials typically develop grasping forepaws, oppose to hooves, flippers or wings. Baby marsupials are called Joeys! Joeys cannot regulate their own heat, and must rely on their mothers pouch for it until they grow their own fur.

Structures Marsupials are widely structurally diverse. Some common structural features can be found in marsupials. The ossified patellae are rarely seen in modern marsupials. Other features such as between the left and right parts of the brain, result in lack of gross communication.

Oldest ancestor Oldest known marsupial was found in china is 15 million years older than the previous record holder dates to 125 million years ago. Could be the oldest aunt or uncle or the great grandparent of all marsupial animals It was capable of climbing trees like other marsupials. were adapted to terrestrial or ground dwelling living. the distant ancestors of modern opossums diverged from the distant ancestors of modern placental mammals about 160 million years ago Australia's marsupials originated in what is now South America not Australia

Ancestry

Convergent and divergent evolution Divergent: Marsupials diverged from Eutherian mammals approximately 90 million years ago. Convergent: There are several cases of convergent evolution between marsupials and placental mammals, in which the two animals have evolved to fill the same ecological niche in different parts of the world. There are burrowing forms, grazing forms, gliding forms, and even long-snouted ant-eating forms which have evolved independently in the two groups

Origin and evolution Marsupials most likely evolved in North America, and continued to expand into South America and the Pacific rim of Asia. During this time of migration the marsupials based in North America became extinct by natural selection following Europe. When North and South America came together during the Pleistocene period, South American marsupials started to migrate back in to the North American population, where the first American opossum evolved. Expanding the species to Australia and New Zealand from North America in the Cretaceous period. During this time, Australia and Antarctica were beginning to break apart. The migration of the marsupial used Antarctica as a route into Australia where they continued an independent evolution.

references http://en.wikipedia.org/wiki/Marsupial http://www.ucmp.berkeley.edu/mammal/marsupial/marsupial.html http://www.nhc.ed.ac.uk/index.php?page=493.168.256

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