This book provides a historical–narrative explanation for a number of osteological features of all groups of marsupials, tests a number of group hypotheses against these, and based on the tests, offers what at present appears to be the most plausible phylogeny, an evolutionary history of these animals, albeit in many ways an inadaquate one. Why my aim is not a “genealogy” but rather a phylogeny, or evolutionary history, is explained more fully below. Any truncated abstractions of phylogeny, as are the cladogram summaries of taxa, should be based on, and in fact readily fall out of, the analysis and testing of numerous interdependent paleontological, historical, and functional-adaptive problems. The scientific validity of phylogenetic reconstruction, and of course any level of confidence in it, depends on such studies (Szalay & Bock, 1991).

There are a number of outstanding general accounts of marsupial biology and evolution (Archer, 1981, 1984a,b; Tyndale-Biscoe, 1973, and others), and books especially dedicated to development, organ systems, and molecules (Tyndale-Biscoe & Renfree, 1987; Tyndale-Biscoe & Janssens, 1988), as well as important scholarly compilations (Cabrera, 1919; Clemens & Marshall, 1976; Marshall, 1981c).