Marsupials Research Paper

Adaptive Radiation, Convergence and the Marsupials
Abstract
Metatheria (Marsupalia) originated upon Laurasia in the Cretaceous with the oldest fossilised remains having been dated to 125 Ma. The first period of metatherian diversification occurred in the late Cretaceous. The K-T mass extinction created an ecological void in which mammalian radiation occurred in the Palaeocene. With South America isolated from North America throughout the Tertiary, there was the second great period of metatherian diversification and there were numerous examples of placental and marsupial convergence. In the Eocene, one line of metatheria radiated across the Antarctic to Australasia and from that lineage the modern Australasian marsupials are descended. There
Placentals have an average body temperature of 38oC whereas marsupials have an average temperature of 35.5oC. This equates to a slower metabolic rate. Advantages of this slower metabolic rate include lower food and water requirements when compared to a placental of a comparable body mass. This adaptation of the entire marsupial infra-class may be indicative of the conditions in South America and Australasia during which time the marsupials were evolving and is evidence of the constraint of marsupial evolution by the overlying ecological niche (in this case on a continental scale) in which they
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