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Australian Marsupials
American Marsupials
References and

Early Evolution

Marsupials, along with placental mammals, are believed to have evolved from Therian mammals. Molecular data indicates marsupials and placental mammals diverged approximately 90 million years ago.

However, molecular data also suggests none of the living marsupial orders are much older than 65million years old, and that all the orders had diverged 50-55 million years ago. Also, whilst all extinct marsupial orders are Gondwanan, none are known that existed before the Palaeocene. This suggests few marsupials survived the KT mass extinction, and that post-KT marsupial evolution mostly occurred in Gondwana.

However, whilst the vast majority of post KT Marsupial evolution occurred in the southern continents, they almost certainly first evolved in the northern continents. With a complete absence of South American Cretaceous marsupial fossils, the oldest South American marsupials are 63-61 million years old fossils found in the Tiupampian levels in Argentina and Bolivia. It is therefore argued that marsupials only migrated to South America from North America by the end of the Cretaceous, between 70 and 65 mya.

Map cret-ter (105K)
Positions of the continents during the Cretaceous-Tertiary boundary, when marsupials were openly migrating from North to South America.

During this period, North American marsupials became extinct, with marsupial extinctions occurring during the Miocene in Europe. This pattern of extinction in the north contrasts to that observed in the south, where marsupials underwent adaptive radiation and continued to migrate throughout Gondwana.

Migration through Gondwana.

Evolution in Australia.

Evolution in the Americas.