Environmental Context of Hominin Foot Evolution.

OBJECTIVES

This study investigates the environmental contexts that influenced the evolution of hominin foot morphology, focusing on when, where, and under what conditions key synapomorphies evolved. We test whether shifts in ecological conditions are associated with changes in locomotor function.

METHODS

We used phylogenetic and biogeographical analyses with paleoenvironmental data to evaluate the relationships between foot morphology and environmental context. Phylogenetic trees were inferred using the fossilized birth-death model and time-calibrated. Multiple topologies were used to explore alternative evolutionary hypotheses. Historical biogeography was reconstructed using BioGeoBEARS. Finally, environmental conditions at key ancestral nodes were inferred by linking reconstructed geographical regions with paleoenvironmental proxies.

RESULTS

The results suggest that the origin of bipedalism likely occurred during intervals of increasing aridity. Later in hominin evolution, wetter environments became more important, and most derived traits evolved during wet or mixed environments. The last common ancestors (LCA) of most Australopithecus and Paranthropus species likely lived in wetter environments, and the LCA of Homo lived in both dry and wet environments. Across all trees, an average of 5.3 synapomorphies evolved in wet environments, 5.0 in dry and wet environments, and 4.3 in mixed environments. The results suggest that a considerable number of foot synapomorphies evolved during periods of ecological transition.

CONCLUSIONS

Ecological flexibility seems to be significant in hominin foot evolution, enabling synapomorphies to persist as hominins faced different environmental conditions. These findings illustrate how environments influenced the evolution of key adaptations in hominins.