ANTRHO105 Exam 3 - Section 5 Bipedalism & Earliest Hominins - VOCAB ONLY

Mosaic

A combination of traits that do not all resemble the same modern comparison group.

Hominin

A member of the human-side lineage after its split from the chimpanzee/bonobo lineage.

Bipedalism

Locomotion on two hind limbs.

Obligate bipedalism

Anatomical reliance on bipedalism as the normal terrestrial locomotor mode.

Habitual bipedalism

Regular use of bipedal locomotion.

Facultative bipedalism

Occasional use of bipedalism when circumstances favor it.

Foramen magnum

Opening in the skull base for the spinal cord; a more inferior/central position supports upright posture.

Lumbar lordosis

Inward curvature of the lower spine that helps balance the trunk over the pelvis.

Pelvis: iliac blade, ilium, ischium

Ilium/iliac blade: upper broad portion of each hip bone

Ischium: lower/posterior portion

A short, broad, reoriented ilium is important to hominin bipedalism.

Abductor muscles

Hip muscles that stabilize the pelvis during single-leg support in walking.

Bicondylar angle

Inward angle of the femur that brings the knee toward the body's midline.

Feeding adaptation hypothesis

Bipedal posture evolved in connection with reaching or obtaining food.

Carrying and provisioning hypothesis

Bipedalism freed hands to carry food, offspring or other resources.

Thermoregulation hypothesis

Upright posture offered thermal advantages such as reduced solar exposure.

Energetics hypothesis

Efficient bipedal locomotion reduced the energy cost of travel.

Non-honing canines

Canines that are not sharpened by an opposing premolar in a honing complex.

Honing complex

A projecting upper canine sharpened against the lower premolar; associated with accommodating dental gaps.

Diastema

A gap between teeth, often accommodating a large opposing canine.

Iliac blades / ilium

The upper broad portions of the hip bones; their shortening and reorientation help stabilize the pelvis in bipedal walking.

Sahelanthropus tchadensis

An early possible hominin from Chad, about 6-7 Ma, with a small brain, reduced canines and evidence interpreted as bipedalism. Browridges

Orrorin tugenensis

An early possible hominin from Kenya, about 6 Ma, combining climbing traits with femoral evidence of bipedalism.

Ardipithecus ramidus ("Ardi")

A 4.4 Ma Ethiopian hominin combining climbing anatomy, a divergent big toe, reduced canines and bipedal pelvic features.

Mosaic evolution

Different traits evolve at different times/rates; bipedalism preceded large brains in hominins.