Question

figure 1. cladogram of selected vertebrate groups
based on the phylogenetic relationships shown in figure 1, which of the following best explains the similarities exhibited by whales, bony fishes, and cartilaginous fishes?
a convergent evolution, because these organisms do not share a recent common ancestor.
b adaptive radiation, because all three groups evolved from a unique, shared common ancestor from the cartilaginous fishes group.
c mutation, because the shared traits can be traced back to a shared recent common ancestor.
d founder effect, because all three groups formerly existed together as one population that then was disrupted, causing speciation.

Explanation:

• Option A: Convergent evolution occurs when unrelated organisms (no recent common ancestor) evolve similar traits due to similar environmental pressures (e.g., aquatic lifestyle for whales, bony fishes, cartilaginous fishes). Whales are mammals, bony fishes and cartilaginous fishes are different fish groups; they do not share a recent common ancestor but have similar adaptations for living in water.
• Option B: Adaptive radiation is rapid diversification from a common ancestor, but whales, bony fishes, and cartilaginous fishes do not share a recent common ancestor from cartilaginous fishes (whales are mammals, not derived from cartilaginous fishes).
• Option C: Mutation leading to shared traits from a recent common ancestor is incorrect because these groups do not have a recent common ancestor.
• Option D: Founder effect is a genetic drift mechanism for small populations, not related to the evolutionary relationships of these major vertebrate groups.

Answer:

A. Convergent evolution, because these organisms do not share a recent common ancestor.