Question

Why does Australia have a great diversity of marsupials (pouched mammals) whereas North America has a great diversity of placental mammals? Refer to the figure below as you answer.

A. Placental mammals cannot survive in the harsh conditions of Australia, so after the continent became isolated the placental mammals evolved to become marsupials.
B. The landmass that broke away to form Australia initially had both marsupials and placental mammals, but the few placental species soon went extinct. The marsupials then diversified in isolation on Australia, whereas placental mammals diversified elsewhere.
C. After a long period of coexistence, marsupials out-competed placental mammals in Australia.
D. Marsupials originated in Australia after the breakup of the continents.

Answer 1

B. Australia's great diversity of marsupials versus North America's diversity of placental mammals is due to Australia's isolation after continental drift, which allowed marsupials to evolve without competition from placental mammals.

Step-by-step explanation:

The reason why Australia has a great diversity of marsupials while North America has a great diversity of placental mammals is due to historical biogeography and evolutionary history.

Specifically, the correct answer to the student's question is option B: 'The landmass that broke away to form Australia initially had both marsupials and placental mammals, but the few placental species soon went extinct.

The marsupials then diversified in isolation on Australia, whereas placental mammals diversified elsewhere.'

Marsupials are predominantly found in Australia, with some species in the Americas. In contrast, placental mammals, after evolving about 110 million years ago, became the dominant land mammals on most continents, largely replacing marsupials and monotremes except in Australia.

The isolation of Australia following the continental drift allowed the marsupials to evolve and diversify without competition from placental mammals, leading to the rich diversity we see today.