MOSAIC · Evolution of the Ape Forelimb: Evidence from Internal Bone Structure

Evolution of the Ape Forelimb: Evidence from Internal Bone Structure

Reconstructing how our ancestors interacted with their environment is a primary goal of paleoanthropology as it improves our understanding of human evolutionary history. In particular, researchers are interested in reconstructing the locomotor behaviour of our fossil ape ancestors of the Miocene (20-5 million years ago [Ma]), because it is key to elucidating the origin of a defining feature of being human: bipedalism, or walking on two feet. Unlike today, in which there are numerous species of monkeys but only four groups of great apes (i.e., orang-utans, gorillas, chimpanzees and bonobos), the Miocene is characterised by the opposite pattern, with a relatively greater number of ape taxa. This makes this epoch particularly interesting as there were several apes that may have led to the African ape and human lineage and reconstructing their behaviour can help elucidate what type of locomotion preceded human bipedalism. Thus, this project aims to reconstruct the locomotor behaviour of the Middle-Late Miocene apes, with an emphasis on the evolution of suspensory/climbing and potential knuckle-walking adaptations, to shed new light on the origin of human bipedalism. The Miocene apes are the direct ancestors of the living apes and exhibit “mosaic morphology”, i.e., they display both primitive (or generalised) and derived (or living ape-like) features that together create combinations of morphologies not found in any living primate, and are characterized by a generalized locomotor repertoire (i.e., arboreal quadrupedalism). There is no consensus among the paleoanthropological community regarding the locomotor behaviour exhibited by the last common ancestor between humans and chimpanzees, and the Miocene apes, with their more generalised morphology, may provide a better ancestral model from which bipedal fossil humans (hominins) – our direct ancestors – evolved. Thus, the objective of this project is to use the internal structure of multiple forelimb bones to reconstruct the locomotor behaviour of several associated skeletons of Miocene apes, namely: Pierolapithecus catalaunicus (12 Ma, Europe), Hispanopithecus laietanus (9 Ma, Europe), Rudapithecus hungaricus (10 Ma, Europe) and Nacholapithecus kerioi (15 Ma, Africa). The capacity of the trabecular (or cancellous) bone to remodel in response to the loading regime during locomotor behaviours may reflect what the animals were actually doing during their lifetime, rather than what they were capable of doing, thus providing a more direct insight into function and how a bone was used during life.

Data: CORDIS, © European Union