Data from: Laetoli footprints reveal bipedal gait biomechanics different from those of modern humans and chimpanzees

Bipedalism is a key adaptation that shaped human evolution, yet the timing and nature of its evolution remain unclear. Here we use new experimentally based approaches to investigate the locomotor mechanics preserved by the famous Pliocene hominin footprints from Laetoli, Tanzania. We conducted footprint formation experiments with habitually barefoot humans and with chimpanzees to quantitatively compare their footprints to those preserved at Laetoli. Our results show that the Laetoli footprints are morphologically distinct from those of both chimpanzees and habitually barefoot modern humans. By analysing biomechanical data that were collected during the human experiments we, for the first time, directly link differences between the Laetoli and modern human footprints to specific biomechanical variables. We find that the Laetoli hominin probably used a more flexed limb posture at foot strike than modern humans when walking bipedally. The Laetoli footprints provide a clear snapshot of an early hominin bipedal gait that probably involved a limb posture that was slightly but significantly different from our own, and these data support the hypothesis that important evolutionary changes to hominin bipedalism occurred within the past 3.66 Myr.两足行走（Bipedalism）是塑造人类演化进程的关键适应性性状，但其演化的时间节点与本质仍未明确。本研究采用新型实验驱动研究方法，对坦桑尼亚莱托利（Laetoli）著名的上新世（Pliocene）人族（hominin）足迹所留存的运动力学特征展开探究。我们分别针对习惯赤足行走的现代人类与黑猩猩开展足迹形成实验，以定量对比二者足迹与莱托利出土足迹的形态差异。研究结果显示，莱托利足迹在形态学上既区别于黑猩猩的足迹，也不同于习惯赤足的现代人类足迹。通过分析人类实验中采集的生物力学数据，我们首次直接将莱托利足迹与现代人类足迹的形态差异，与特定的生物力学变量建立对应关联。我们发现，莱托利古人类在两足行走时，足触地瞬间的肢体屈曲程度大概率高于现代人类。莱托利足迹为早期人族两足行走步态提供了清晰的快照式记录：其肢体屈曲姿势虽与现代人类存在细微但具有统计学显著性的差异；本研究数据亦支持下述假说：人族两足行走的重要演化改变发生在过去366万年（3.66 Myr）以内。