One primitive trait of Ardipithecus ramidus is its:

• A. fully bipedal locomotion like modern humans
• B. opposable big toe adapted for grasping
• C. short canine teeth similar to modern humans
• D. large brain size comparable to Homo sapiens

Answer: (B)

Verified step by step guidance

1. Understand the context: Ardipithecus ramidus is an early hominin species that lived approximately 4.4 million years ago. It is considered a transitional species between earlier primates and later hominins, showing a mix of primitive and derived traits.
2. Define 'primitive trait': A primitive trait is a characteristic inherited from an ancestor that has not undergone significant evolutionary change. In this case, we are looking for a feature that is more similar to earlier primates than to modern humans.
3. Analyze the options: Evaluate each trait listed in the problem to determine whether it is primitive or derived. For example, 'fully bipedal locomotion like modern humans' is a derived trait, as it is a hallmark of later hominins. Similarly, 'short canine teeth similar to modern humans' and 'large brain size comparable to Homo sapiens' are also derived traits.
4. Focus on the opposable big toe: The opposable big toe adapted for grasping is a primitive trait because it is a feature seen in earlier primates, allowing them to grasp branches and climb trees. This trait is not present in modern humans, who have a non-opposable big toe adapted for bipedal walking.
5. Conclude: The primitive trait of Ardipithecus ramidus is the opposable big toe adapted for grasping, as it reflects its ancestral connection to arboreal primates and distinguishes it from later hominins with fully bipedal adaptations.