Passage Summary: Predators usually have short elbow bones because they need to move fast to catch food. Since this extinct animal also had short elbow bones, the author concludes it was probably a hunter.

Conclusion: The extinct mammal Megatherium was likely a predatory mammal.

Reasoning: Short elbow bones allow for faster limb movement, which is a trait predators need and generally possess, and Megatherium had these short elbow bones.

Analysis: The author commits a classic error by confusing a necessary condition with a sufficient one. While predators generally have short olecranon processes, the argument fails to consider that non-predators might also possess this trait for different evolutionary reasons. The logic incorrectly implies that because predators have the trait, anyone with the trait must be a predator. Look for an answer choice that identifies this failure to consider alternative explanations for the physical trait.