Primate Bipedalism and Brachiation Lecture Notes

Comprehensive vocabulary flashcards covering the anatomical and evolutionary aspects of primate locomotion, specifically brachiation and the skeletal adaptations for bipedalism and running.

Brachiation

A major form of arboreal locomotion in primates where true brachiators, like gibbons, can reach speeds of $35\,mph$ and covers $20\,feet$ per swing.

Primate Brachiation Adaptations

Skeletal features including a dorsally positioned scapula, rounded humeral head for circumduction, long arms, rotating wrists, short nails, and hook-like phalanges.

Hominoid Pelvis

Alterations for erect posture where the pelvis takes on the brunt of weight bearing, becoming thicker, less elongate, and having a basin-shaped ilium.

Barrel-shaped rib cage

A trunk modification that allows for a distinct waist, which enables greater rotation of the pelvis without upper body involvement and separates respiration from locomotion.

Kyphoses

Primary curvatures of the vertebral column located in the thoracic and sacral regions that are concave ventrally and determined by the shape of the vertebral body.

Lordoses

Secondary curvatures of the vertebral column located in the cervical and lumbar regions that are concave dorsally, determined by the shape of IV discs, and molded over time and use.

Angle of inclination

The angle of the joint at the acetabulum where the femur head is set away from the shaft; it becomes less obtuse with age and is generally less in women to increase the arc and range of motion.

Torsion angle

A measure of the alignment of the femur with the tibia that contributes to a knock-kneed stance and is greater in females due to a wider pelvis.

Foot Modifications for Bipedality

Includes a big toe that is no longer opposable, shorter digits, and a broader plantar surface for increased surface area.

Arches of the Foot

Longitudinal and transverse structures supported by ligaments and long tendons that eliminate tensile stress by converting force to compressive stress, acting as shock absorbers and springboards.

Evolutionary Reasons for Bipedality

Proposed adaptations for predator avoidance (seeing over high objects) and the ability to carry objects.

Bipedal Running Adaptations

Skeletal changes such as longer legs for increased stride, a long Achilles tendon for elastic energy, and larger gluteal muscles to drive the basin-like pelvis.

Rhomboids (Human vs. Chimp)

In chimpanzees, these muscles attach to the skull; in humans, they attach to the vertebrae.

Trapezius (Human vs. Chimp)

In chimpanzees, these muscles attach to the skull; in humans, they attach to the nuchal ligament of a smaller skull.

Nuchal ligament

A structure in humans that anchors the skull and reduces dorso-ventral bounce during bipedal running.