The theory of a land bridge between south america and africa as an explanation for similar fossils on the two continents is not supported because

It could not explain the main mechanism behind the movement of the continents

Explanation:

The continental drift theory refers to the floating of the continents across the ocean water body over a specific period of time, with respect to the poles. It was initially discovered by Alfred Wegener. He forwarded many evidences supporting this theory, such as the appearance of similar fossil assemblages and rock layers in different continents, and matching of the continental margin. But the main mechanism that initiates continental motion was not able to explain.

The seafloor spreading concept was also not cleared by that time, which leads to the enlargement of the ocean basin.

This is why the theory of land bridge connecting Africa and South America for getting similar fossils at separated continents was not supported.

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explanation: