Trabecular evidence for a human-like gait in Australopithecus africanus

Area of Science:

• Paleoanthropology
• Biomechanics
• Skeletal Biology

Background:

• Early hominin bipedalism is established, but the degree of lower limb joint extension during walking remains debated.
• Evidence regarding whether Australopithecus species utilized extended or flexed hip, knee, and ankle postures, akin to modern humans or apes, is mixed.

Purpose of the Study:

• To investigate the locomotor behavior of Australopithecus africanus by analyzing ankle joint loading during bipedalism.
• To compare the joint loading patterns of Australopithecus africanus with those of modern humans and chimpanzees.

Main Methods:

• Established a relationship between ankle joint loading orientation and trabecular bone orientation in the distal tibia for chimpanzees and humans.
• Utilized microCT scans to analyze trabecular bone strut orientation in fossil hominin tibiae from Sterkfontein, specifically two specimens of Australopithecus africanus.

Main Results:

• A strong correlation was found between ankle joint loading and trabecular bone orientation in extant species.
• Analysis of Australopithecus africanus tibiae indicated primary ankle loading in a relatively extended posture, similar to modern humans and distinct from chimpanzees.
• Trabecular properties in Australopithecus africanus were found to be intermediate between chimpanzees and humans.

Conclusions:

• Australopithecus africanus likely walked with an extended lower limb posture, similar to Homo.
• The findings suggest efficient bipedal locomotion in Australopithecus africanus, challenging previous assumptions of more ape-like gait.