Comparative Reconstruction of Ape and Hominin Locomotor ontogeny

ended

Of all the traits that define humans, bipedal locomotion likely evolved first. How and why bipedalism evolved in the fossil human (hominin) lineage are fundamental questions in palaeoanthropology. An underexplored dimension of “how” bipedalism evolved is its growth and development (ontogeny). Humans locomotion develops much slower than those of other apes. Modern humans are also fully terrestrial, while the other African apes transition from predominantly arboreal locomotion using their upper limbs as juveniles to predominantly terrestrial knuckle-walking as adults. The importance of arboreal locomotion throughout hominin evolution has remained debated since the 1980s. However, since all extant apes are most arboreal as juveniles, the answers to this debate are most likely found in juvenile hominins.We know little about hominin locomotor ontogeny and the behaviour of juveniles due to (1) a lack of fossils and (2) limited tools for behavioural reconstruction. CRAHL applies recent methodological advances to both well-studied and newly discovered fossils to overcome these limitations, and will be the first to investigate the evolutionary pattern of hominin locomotor development. Bones can dynamically adapt to changes in loading direction, magnitude, and frequency by altering the structure of trabecular bone, the 3D mesh-like structure found underneath joint surfaces. Trabecular structure can therefore provide a functional record of developmental variation in loading conditions as animals learn to locomote. By using state-of-the-art methods for analysing age-related changes in trabecular bone structure throughout the skeleton, CRAHL will reconstruct how quickly hominins learned to locomote and the variety of postures they assumed, including arboreal versus terrestrial locomotion. By combining state-of-the-art methods new fossil discoveries, CRAHL sheds new light on the evolution of two defining human traits: slow development and fully terrestrial bipedalism.