The sentence discusses the evolution of advanced tortoises and their specific adaptations for terrestrial life, including high-domed shells and columnar, elephantine feet. To select the correct word for the blank, we need to consider the context.

1. "Independently" is the correct choice because it conveys that these adaptations evolved separately and autonomously on each continent without relying on each other. This implies that the evolution of these traits on one continent did not influence or dictate their evolution on another.

2. "Simultaneously" would be an incorrect choice because it suggests that these adaptations occurred at the same time on each continent, which may not be the case based on the sentence. The use of "multiple times" in the opening phrase implies separate occurrences.

3. "Interchangeably" is not suitable because it implies that the adaptations were used in place of each other on different continents, which doesn't accurately describe their independent evolution.

4. "Paradoxically" and "symmetrically" do not fit the context because they do not convey the idea of separate and independent evolution on each continent. Instead, they introduce different connotations unrelated to the sentence's intended meaning.

In summary, "independently" is the best choice as it precisely communicates the concept of separate and autonomous evolution of these adaptations on each continent.

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