Department of Sociology, Anthropology and Social Work, Seton Hall University, 400 South Orange Avenue, South Orange, NJ 07079, USA.
J Hum Evol. 2013 Jul;65(1):65-78. doi: 10.1016/j.jhevol.2013.04.002. Epub 2013 May 31.
The origin and evolution of early Pleistocene hominin lithic technologies in Africa occurred within the context of savanna grassland ecosystems. The Nachukui Formation of the Turkana Basin in northern Kenya, containing Oldowan and Acheulean tool assemblages and fossil evidence for early members of Homo and Paranthropus, provides an extensive spatial and temporal paleosol record of early Pleistocene savanna flora. Here we present new carbon isotopic (δ(13)CVPDB) values of pedogenic carbonates (68 nodules, 193 analyses) from the Nachukui Formation in order to characterize past vegetation structure and change through time. We compared three members (Kalochoro, Kaitio, and Natoo) at five locations spanning 2.4-1.4Ma and sampled in proximity to hominin archaeological and paleontological sites. Our results indicate diverse habitats showing a mosaic pattern of vegetation cover at each location yet demonstrate grassland expansion through time influenced by paleogeography. Kalochoro floodplains occurred adjacent to large river systems, and paleosols show evidence of C3 woodlands averaging 46-50% woody cover. Kaitio habitats were located along smaller rivers and lake margins. Paleosols yielded evidence for reduced portions of woody vegetation averaging 34-37% woody cover. Natoo environments had the highest percentage of grasslands averaging 21% woody cover near a diminishing Lake Turkana precursor. We also compared paleosol δ(13)CVPDB values of lithic archaeological sites with paleosol δ(13)CVPDB values of all environments available to hominins at 2.4-1.4Ma in the Nachukui and Koobi Fora Formations. Grassy environments became more widespread during this interval; woody canopy cover mean percentages steadily decreased by 12%. However, significantly more wooded savanna habitats were present in the vicinity of lithic archaeological sites and did not mirror the basin-wide trend of grassland spread. Hominin lithic archaeological sites consistently demonstrated woody cover circa 40% throughout our study interval and were 4-12% more woody than coeval basin environs. We propose that Turkana Basin early tool makers may have preferred a more wooded portion of the savanna ecosystem to reduce heat stress and to gain differential access to potable water, raw materials, animal carcasses, and edible plants.
非洲早更新世人类石器技术的起源和演变发生在热带稀树草原生态系统的背景下。肯尼亚北部图尔卡纳盆地的 Nachukui 组包含了 Oldowan 和 Acheulean 工具组合以及早期人类和傍人属的化石证据，为早更新世热带稀树草原植物提供了广泛的时空古土壤记录。在这里，我们提供了 Nachukui 组中新的碳同位素（δ(13)CVPDB）值（68 个结核，193 个分析），以描述过去的植被结构和随时间的变化。我们比较了三个成员（Kalochoro、Kaitio 和 Natoo）在五个地点的样本，这些地点跨越了 240-140 万年，并且与人类考古和古生物学遗址相近。我们的结果表明，每个地点都存在多样化的生境，表现出植被覆盖的镶嵌模式，但随着时间的推移，由于古地理的影响，草原面积不断扩大。Kalochoro 洪泛区位于大型河流系统附近，古土壤显示出 C3 林地的证据，平均木本植物覆盖率为 46-50%。Kaitio 生境位于较小的河流和湖泊边缘。古土壤显示出木本植被减少的证据，平均木本植物覆盖率为 34-37%。Natoo 环境的草原比例最高，平均为 21%，位于正在缩小的图尔卡纳湖前身附近。我们还比较了 Nachukui 和 Koobi Fora 组中 240-140 万年前人类可用的所有环境的石器考古遗址的古土壤 δ(13)CVPDB 值与古土壤 δ(13)CVPDB 值。在这段时间内，草原环境变得更加广泛；木本树冠覆盖率的平均百分比稳步下降了 12%。然而，在石器考古遗址附近存在更多的林地热带稀树草原生境，与盆地范围内的草原蔓延趋势并不相符。人类石器考古遗址在整个研究期间始终表现出约 40%的木本覆盖度，比同期盆地环境的木本覆盖度高出 4-12%。我们提出，图尔卡纳盆地早期的石器制造者可能更喜欢热带稀树草原生态系统的更具树木的部分，以减少热应激，并获得对饮用水、原材料、动物尸体和可食用植物的不同获取途径。
