Passage Summary: Some experts think certain dinosaurs were long-term parents because of their nest fossils, but since crocodiles build the same nests and are quick to leave their young, the nest evidence is shaky.

Conclusion: The discovery of fossilized nests does not conclusively prove that those dinosaur species guarded their young for an extended period.

Reasoning: While some scientists use nests as evidence for long-term care, modern crocodiles build similar nests but only provide care for a very short time.

Analysis: The argument uses a comparative approach to undermine a specific piece of evidence. By showing that a similar physical trait (the nest) exists in a species that does not exhibit the behavior in question (long-term guarding), the author creates a gap in the paleontologists' logic. Look for an answer that completes the thought by pointing out that the evidence is insufficient to support the original theory.