Skeletal and Dental Anatomy; Locomotion and Posture Midterm 1.3

What is the cranium, and why is it important for studying primate evolution?

The cranium is the skull, which houses the brain and provides attachment points for muscles involved in chewing and movement. Its shape and size reflect brain expansion in hominins.

What is the mandible, and why is it significant in primate evolution?

The mandible is the lower jawbone. It is important for studying diet and chewing adaptations in primates, as well as changes in facial structure over evolutionary time.

What is the maxilla, and how does it contribute to primate morphology?

The maxilla is the upper jawbone. It plays a role in facial structure, housing the upper teeth, and influencing dietary adaptations.

What is the scapula, and how does it relate to primate locomotion?

The scapula, or shoulder blade, is key in understanding locomotion. Apes have a more dorsally placed scapula suited for suspensory movement, while humans have modifications for bipedal posture.

What is the humerus, and how does it differ between primates?

The humerus is the upper arm bone. In apes, it is adapted for climbing and suspensory locomotion, whereas in humans, it is more specialized for manipulation rather than weight-bearing.

What is the ilium, and why is it crucial for bipedalism?

The ilium is part of the pelvis. In humans, it is short and broad, aiding in balance and weight transfer for bipedalism. In chimpanzees, it is taller and more oriented for quadrupedalism and climbing.

What is the femur, and how is it adapted for bipedalism?

The femur is the thigh bone. In humans, it has a valgus angle (inward slant) to keep the knees and feet under the body's center of mass, essential for efficient bipedal walking.

What is the tibia, and how does it support bipedalism?

The tibia is the shinbone. It is adapted in humans to bear weight efficiently, with a broad platform at the top to support the body's mass.

What is the hallux, and how does it differ between humans and apes?

The hallux is the big toe. In humans, it is aligned with the other toes for efficient walking, while in apes, it is opposable for grasping and climbing.

What are the major differences between the human pelvis and that of a chimpanzee?

The human pelvis is shorter and broader, with laterally oriented iliac blades, which improve stability for bipedalism. The chimpanzee pelvis is taller and narrower, more suited for quadrupedal movement and climbing.

What is the 'pelvic tilt' mechanism, and why is it important for bipedalism?

The pelvic tilt mechanism involves the gluteal muscles (gluteus medius and minimus) stabilizing the pelvis during walking, preventing excessive side-to-side motion.

What is distinctive about the human femur compared to a chimpanzee’s?

The human femur has a pronounced valgus angle, bringing the knees under the body’s center of mass for efficient bipedal walking. Chimpanzees lack this angling and have a straighter femur.

How is the human knee joint adapted for bipedalism?

The human knee joint has a larger lateral condyle and locking mechanisms that help maintain stability and reduce energy expenditure while walking upright.

What are the key spinal adaptations for bipedalism?

The human spine has an S-curve, which helps absorb shock and balance weight over the pelvis, contrasting with the more C-shaped spine of quadrupedal apes.

How does the human pelvis aid in bipedal locomotion?

The broad, short shape of the human pelvis improves balance and allows for better attachment of stabilizing muscles, aiding in efficient upright walking.

What might have been the major adaptive advantage of bipedalism for hominins?

Bipedalism freed the hands for tool use, allowed for greater energy efficiency over long distances, improved thermoregulation, and enabled better visibility in open environments.

When do we first see evidence of adaptations to bipedalism in the hominin fossil record?

The earliest evidence appears around 6-7 million years ago with Sahelanthropus tchadensis, followed by Orrorin tugenensis (~6 Ma) and Ardipithecus ramidus (~4.4 Ma).

Were all hominins bipedal in the same way?

No, early hominins like Ardipithecus and Australopithecus retained some climbing adaptations, whereas later species, including Homo erectus, had more human-like, fully committed bipedalism.

What evidence suggests that Ardipithecus and Australopithecus were still adept at climbing trees?

They had curved finger bones, a more grasping big toe (Ardipithecus), and upper limb proportions that suggest they still relied on tree climbing alongside bipedalism.

How does Homo habilis provide evidence of both bipedalism and climbing ability?

While Homo habilis had a more modern foot structure, its limb proportions and hand morphology indicate that it retained some climbing adaptations.