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ORIGIN AND EVOLUTION OF MARSUPIALS
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- Marsupials (Metatherians) are thought to have evolved, along with placental (Eutherian) mammals, from
Therian mammals.
- Marsupials diverged from Eutherian mammals approximately 90 million years ago.
- Marsupials probably evolved in North America, expanded into South America and the
Pacific rim of Asia. During this period of migration the North American marsupials
became extinct, followed by extinctions in Europe during the Miocene epoch of the Tertiary period.
- When North and South America rejoined in the Pleio-pleistocene, South American marsupials
migrated back into North America, where Didelphis virginiana,
the American opossum evolved.
- Marsupials began to migrate to Australia and New Zealand from North America in the late Cretaceous or early Tertiary period.
The route of migration crossed Antarctica and into Australia.
As Australia broke off from Antarctica and moved northwards, its isolation
from other landmasses was complete and the independent evolution of marsupials in
Australia and New Zealand began.
- Below is a possible phylogenetic tree for the origins of marsupials.
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