[Campbell Biology P.592] Based on Figure 25.22, which of the following statements about the ... | Practice Question

Based on Figure 25.22, which of the following statements about the adaptive radiation of mammals is accurate?

  • A: Monotremes are the most speciose group among mammals shown, with 6,028 species.
  • B: The major diversification of Eutherians (placental mammals) occurred roughly before 150 million years ago.
  • C: All three major mammal lineages (Monotremes, Marsupials, Eutherians) diverged from a common ancestral mammal approximately 180-200 million years ago.
  • D: The ancestral cynodont is more closely related to Marsupials than to Monotremes.

Explanation

Figure 25.22 shows that Monotremes, Marsupials, and Eutherians all originate from a common ancestral mammal, with the divergence point for these three lineages occurring approximately between 180-200 million years ago on the timeline. Option A is incorrect because Monotremes only have 5 species, while Eutherians are the most diverse with 6,028 species. Option B is incorrect as the major diversification of Eutherians is shown to have occurred from approximately 150 million years ago onwards, not before. Option D is incorrect because all three groups are equally descended from the ancestral mammal, which came from the ancestral cynodont.