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Fig. 2. Phylogeny of some American marsupials, based on Palma and Spotorno
(1999) and Nowak
(1999). Although scansorial
and arboreal locomotor adaptations evolved more than once in the family
Didelphidae, it is likely that the common ancestor was a terrestrial form.
Furthermore, Nowak (1999) and
Cartmill (1972) suggest that
the terrestrial Monodelphis genus retains the primitive condition to
the greatest degree.