Paleoanthropological Research in the Kibish Formation, Ethiopia

解剖学上现代人类的起源是当今人类进化中最令人兴奋和激烈争论的话题之一。大量基因研究的结果表明，现代人类在过去20万年的某个时候出现在非洲，随后迁移到世界其他地区。虽然这一时期非洲人类进化的古生物学记录似乎支持这一设想，但证据受到许多不确定性的困扰，因为许多关键的化石都是从碎片遗骸中发现的，而且很难确定准确的年代。例如，据称在南非发现的早期现代人遗骸非常残缺不全，而在坦桑尼亚和肯尼亚发现的更完整的遗骸则很难确定确切的年代。30多年来，来自埃塞俄比亚西南部基比什地层的古生物遗骸为10万多年前撒哈拉以南非洲解剖学上的现代人提供了重要证据。然而，基比什化石也一直是争论的主题，因为它们的实际年龄不确定，而且有迹象表明，在这些沉积物中保存着两种非常不同类型的原始人类化石——一种相对古老，另一种更现代。确定这些化石的实际年代将大大有助于我们了解人类在非洲进化的时间，以及唯一导致现代人类的血统起源。1999年，在基比什地层进行了一次初步调查考察，以探索继续在那里进行实地考察的可能性和前景。1999年季节的结果包括1967年化石发现地区基比什组的初步地层格架，以及1967年头骨遗骸周围凝灰岩沉积物的40Ar/39Ar年代。这些表明，奥莫1号和奥莫2号头骨遗骸不太可能来自同一地层层位，这些古人类的年龄在10万到20万年之间，而其他沉积物可能可以追溯到30万年。我们还将基比什组已知的哺乳动物群增加了一倍，并在整个基比什组发现了石器，包括与带有切割痕迹的动物遗骸相关的工具。研究的总体目标是：1)通过额外的实地调查和分析，加强和完善基比什组年龄的数值控制；2)完善已有化石的地层和时间框架，为未来的研究建立广泛的区域框架；3)将基比什组沉积学与区域气候变化联系起来；4)在这个年代学、地层学和沉积学框架内确定更多的古生物学和考古学地点。这些目标的实现将极大地推进我们目前对过去30万年中人类进化和现代人类在非洲起源的理解，即人类物种首次进化的地点和时间。

The origin of anatomically modern humans is one of the most exciting and hotly debated topics in human evolution today. The results of numerous genetic studies indicate that modern humans arose in Africa sometime during the last 200,000 years and subsequently migrated to other parts of the world. While the paleontological record of human evolution in Africa during this time period seems to support this scenario, the evidence is beset by many uncertainties as many of the critical fossils are known from fragmentary remains and have proved difficult to date precisely. For example, the purported remains of early modern early modern humans from South Africa are very fragmentary, while the more complete remains from Tanzania and Kenya have proved very difficult to date confidently. For over three decades, the paleontological remains from the Kibish Formation in southwestern Ethiopia have provided critical evidence of anatomically modern humans in subsaharan Africa more than 100,000 years ago. However, the Kibish fossils have also been the subject of debate because of uncertainties regarding their actual age, and the indications that two very different types of fossil hominid are preserved within these deposits- one relatively archaic and another more modern. Resolution of the actual ages of these fossils will contribute substantially to our understanding of the timing of human evolution in Africa and the origin of lineage leading uniquely to modern humans. An initial survey expedition in the Kibish Formation was undertaken in 1999 to explore the possibilities and promise of continued fieldwork there. Results of the 1999 season include a preliminary tephrostratigraphic framework for the Kibish Formation in the area where the 1967 fossils were discovered and 40Ar/39Ar dates for tuffaceous deposits bracketing the 1967 cranial remains. These indicate that the Omo 1 and Omo 2 cranial remains are unlikely to have come from the same stratigraphic horizon and that the hominids are between 100,000 and 200,000 years old with other deposits probably extending back to 300,000 years. We also doubled the mammalian fauna known from the Kibish formation and found stone tools throughout the Kibish Formation, including instances of tools associated with faunal remains bearing cutmarks. The overall goals of the research are: 1) To strengthen and refine the numerical control on the age of the Kibish Formation through additional fieldwork and analyses; 2) to refine the stratigraphic and temporal framework for previously collected fossils and establish a broad regional framework for future research; 3) to relate the sedimentology of the Kibish Formation to regional climatic changes; and 4) to locate additional paleontological and archeological localities within this chronometric, stratigraphic and sedimentological framework. Accomplishment of these goals will greatly advance our current understanding of human evolution and modern human origins in Africa during the past 300,000 years, the place and time in which or species first evolved.