Abstract The world's oldest known stone tools discovered at the Pliocene site of Lomekwi 3 (LOM3) in the Nachukui Formation, northern Kenya, signals a prodigious behavioral change in the hominin lineage. LOM3, dated to 3.3 Ma, is significantly earlier than the first appearance of genus Homo and coincides with the onset of the Mid-Pliocene Warm Period, warranting new phylogenetic and environmental explanations for the origins of hominin stone tool making behaviors. Here we examined Pliocene paleoenvironments (4.3–3.0 Ma) within the Omo-Turkana Depression (OTD) with paleosol pedogenic carbonate (PC) and faunal enamel carbonate (EC) δ13C and δ18O values. Amidst the gradual shift toward more grassy environments, intranodular δ13CPC and δ18OPC variation slightly increased through time. Three of fourteen ungulate herbivore taxa yielded statistically significant increases in δ13CEC values. When all ungulate herbivore δ13CEC values are grouped by feeding categories (C3-browsers, C3-C4-mixed feeders, C4-grazers) there is evidence that the C3-C4-mixed feeding niche contracted and shifted toward the C4-grazing niche as hominins expanded their dietary breadth during the middle Pliocene. Only one of nine taxa showed a significant decrease in δ18OEC values across the study interval. Abrupt, significant environmental perturbations are not evident during LOM3 times in the OTD, casting doubt on variability selection or pulsed humidity as selective forces for middle Pliocene technological innovations. We propose that a long-term feedback system involving gradual environmental changes and biotic dietary competition influenced a suite of hominin adaptations to a broad dietary niche, culminating in the origins of stone tool making behaviors.

中文翻译：

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饮食生态位扩张和上新世环境变化对石器制造起源的影响

摘要 在肯尼亚北部 Nachukui 组的 Lomekwi 3 (LOM3) 上新世遗址发现的世界上已知最古老的石器标志着人类谱系发生了巨大的行为变化。LOM3 可追溯到 3.3 Ma，明显早于人属的首次出现，并且与中上新世暖期的开始相吻合，为人类石器工具制造行为的起源提供了新的系统发育和环境解释。在这里，我们用古土壤成土碳酸盐 (PC) 和动物群釉质碳酸盐 (EC) δ13C 和 δ18O 值检查了 Omo-Turkana 凹陷 (OTD) 内的上新世古环境 (4.3-3.0 Ma)。在逐渐转向更多草地环境的过程中，结节内 δ13CPC 和 δ18OPC 变化随时间略有增加。十四个有蹄类食草动物分类群中的三个在 δ13CEC 值上产生了统计学上的显着增加。当所有有蹄类食草动物 δ13CEC 值按饲养类别（C3 浏览器、C3-C4 混合饲养者、C4 食草动物）分组时，有证据表明 C3-C4 混合饲养生态位收缩并向 C4-放牧生态位转变为人族在上新世中期扩大了他们的饮食范围。在整个研究间隔内，九个分类群中只有一个显示出 δ18OEC 值的显着下降。在 OTD 的 LOM3 时期，突然的、显着的环境扰动并不明显，这使人们对可变性选择或脉冲湿度作为中上新世技术创新的选择力产生了怀疑。