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Michael Fontain
Dr. Horn
Anatomy & Physiology: Evolution/ Classification
14 March 2008
Metatheria, mammals with folds or pouches on the ventral surface that cover reproductive organs, is an infraclass that comprises all marsupials. They can be classified under many taxonomic groups, although they were once all classified under one single Order called Marsupialia. New information from studies of molecular biology allows for the more detailed organization of marsupial groups, and studies of morphology and fossil records support this change in classification (Diversity).
The first taxon is called a Domain, which is the highest grouping of living things, and includes prokaryotes (Eubacteria and Archaebacteria) and eukaryotes (cellular life with a nucleus and other membranes). Metatheria are heterotrophic multi-cellular organisms with eukaryotic cells. (Diversity).
The second rank is Kingdom, and Metatheria is contained in the Animal Kingdom. The distinguishing characteristics of animals compared to other eukaryotes like plants and fungi include a non-walled cell, mostly sexually reproductive creatures that form a zygote as a result of mating, relatively faster and more complex motion (Diversity).
The Chordata Phylum is the next grouping. The uniting characteristics of chordates are a notochord, endostyle, dorsal hollow nerve cord, post-anal tail, and pharyngeal slits or pouches. Its sub-Phylum Vertebrata has animals that have a reduced notochord replaced by a bony vertebral column (Diversity).
The Class of mammals, also known as Mammalia, is the next major grouping that marsupials fall under. This Class has similarities that suggest they are monophyletic: hair at some stage in life, . Most mammal Orders are viviparous (animals that put forth living young and not eggs) with the exceptions of the oviparous non-placentals Orinthorhynchus anatinus and Tachyglossus aculeatus (Random House 864).
Metatheria...