Question

Which hominin had the best arboreal capabilities (look at both upper and lower extremities)? Make sure you explain your answer and give me at least one features that backup your claim. The feature that you choose has to be from lower extremities.

Which hominins was the first to not just be an upright walker but an obligate biped (this means you have no choice but to walk on two legs)? Make sure you explain your answer using the same feature that you used when looking at the other hominin for comparative purposes.

Lastly, I would like you to give a short summary of the notable transformations in locomotor strategy that occur over time as seen from Ardipithecus ramidus to Australopithecus afarensis.

Answer 1

Ardipithecus ramidus is the hominin with best arboreal capabilities. Though Ardipithecus walked bipedally on the ground, it spent much of the time in the trees. This arboreal capacity was due to certain unique body features. The long forelimbs and fingers were among the features. The divergent and grasping first toe was another important feature. The curved fingers and toes of the lower extremities helped Ardipithecus to make a firm grasp on the trees.

Australopithecus afarensis, though retained ape like features such as cranially oriented glenoid and long, curved pedal and manual phalanges, it was considered as first obligate bipedal. The clearly derived bipedal adaptations of A. afarensis include almost human like pelvis and wide sacrum and human like bicondylar angle of the femur bones. A. afarensis lacked relatively long fingers and toes and the grasping foot that are important features for efficient arboreal capabilities. Thus, all the features combined makes A. afarensis first obligate bipedal.

The notable transformations in locomotor strategy that was observed in between Ardipithecus ramidus and Australopithecus afarensis include change in the structure of upper limbs and lower limbs and changes in the pelvic-sacral region.