Final answer:
The true statement about the major evolutionary faunas is B) the Modern fauna originated in the Cambrian, during a period known as the Cambrian explosion. This period was marked by rapid evolution and diversification of many animal phyla.
Step-by-step explanation:
The question pertains to the major evolutionary faunas and their history. Of the provided options, B) the Modern fauna originated in the Cambrian is true in the context of major evolutionary changes. The Cambrian period, approximately 542-488 million years ago, saw the emergence of most animal phyla we recognize today—including forms similar to echinoderms, mollusks, worms, arthropods, and chordates—during a period referred to as the Cambrian explosion. It was a time characterized by the most rapid evolution of new animal phyla and a significant increase in animal diversity.
The Cambrian fauna, while having no direct representatives today, is not entirely extinct, as lineages originating from this period have given rise to modern species. Therefore, option A is incorrect. As for option C, the Paleozoic fauna did not rebound to previous levels of diversity immediately after the Permian extinction; it was a catastrophic event that led to a significant loss in biodiversity, paving the way for different evolutionary paths. Lastly, option D is also incorrect, as the Modern fauna has not persisted for the least amount of time. The Modern fauna represents a broad evolutionary lineage whose inception dates back to the diversification events after the Cambrian.