Final answer:
Both apes and humans have a coccyx as part of their post-crania. The coccyx is a vestigial structure in humans, indicative of a lost tail. The study of hominin ancestors illustrates the evolutionary transition from arboreal to bipedal locomotion.
Step-by-step explanation:
The post-crania refers to the parts of the skeleton apart from the skull. Both apes and humans have a post-crania, which includes the coccyx. The coccyx, or tailbone, is a vestigial structure in humans, reminiscent of a lost tail. Although the overall morphology of apes and humans is different, the presence of a coccyx can be found in both. In human evolution, morphological changes, such as bipedalism, led to the reduction and transformation of the coccyx compared to other primates. This fact ties into the study of hominins, where changes in the post-crania have provided significant insight into the locomotion and related lifestyle adaptations.
Indeed, while looking at our hominin ancestors like Australopithecus afarensis, we observe that while they have traits related to arboreal activities, like long curved fingers, they also feature aspects such as a pelvis shape more reminiscent of bipedal hominins like humans. This indicates that while some ancient hominins retained arboreal features, they also adopted bipedal locomotion, a definitive trait in human evolution. Thus, apes and humans, as part of the family of hominoids, share many skeletal characteristics, including the presence of a coccyx, but differ significantly in their adaptations and morphology.