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Origin and Early Evolution of Marsupials

William A. Clemens
Evolution
Vol. 22, No. 1 (Mar., 1968), pp. 1-18
DOI: 10.2307/2406645
Stable URL: http://www.jstor.org/stable/2406645
Page Count: 18
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Origin and Early Evolution of Marsupials
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Abstract

Although many significant discoveries, some attributable to the development of new collecting techniques, have been made in recent years, the fossil record of mammalian evolution in the Mesozoic and early Cenozoic remains fragmentary. Keeping this limitation in mind, the available data can be employed in construction of a provisional history of the origin and early evolution of the Marsupialia. Recent studies by Kermack, Mills, Patterson, and others strongly suggest the ancestry of marsupials and placentals can be traced back to the Welsh Rhaetic panotheres. Pappotherium and other therians of eutherian-metatherian grade and late Early Cretaceous age probably either represent the dental characters of the most recent common ancestors of the Marsupialia and the Eutheria or may be members of this ancestral stock. Differentiation of the Marsupialia in the early Late Cretaceous was followed by a major adaptive radiation in North America. All these Cretaceous lineages except the didelphid, represented by the species of Alphadon, became extinct at the end of the period. In characters of its dentition Alphadon is the Late Cretaceous marsupial most closely resembling the Albian therians of eutherian-metatherian grade. Apparently Alphadon or other didelphid marsupials with similar dentitions successfully colonized South America and Australia in the Late Cretaceous or early Cenozoic. The appearance of marsupials in western Europe in the early Eocene seems to have been the result of a later wave of mammalian dispersal into the Old World including Peratherium, a descendant of Alphadon.

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