Final answer:
The research indicating that one type of sponge is more closely related to non-sponge animals supports the idea of a sponge-like common ancestor for animals, illustrating the complexity and diversity of the animal kingdom's evolutionary history.
The correct answer to the student's question is: C. A common ancestor of animals was a sponge-like animal.
Step-by-step explanation:
Research suggests that one type of sponge is more closely related to non-sponge animals than to other sponges. This finding suggests that the classifications within the animal kingdom may be more complex than previously understood. Essentially, this evidence supports the idea that a common ancestor of animals may have been sponge-like, implying that the emergence of specialized tissues and differentiation likely occurred after some sponges had already diverged from the main lineage that led to more complex organisms. This does not mean that sponges do not belong in the animal kingdom but rather emphasizes the evolutionary process that gave rise to the diversity of animal life, including various multicellular structures and complexities.