Revised stratigraphy of Area 123, Koobi Fora, Kenya, and new age estimates of its fossil mammals, including hominins
Revised stratigraphy of Area 123, Koobi Fora, Kenya, and new age estimates of its fossil mammals, including hominins
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DOI：
10.1016/j.jhevol.2006.05.005
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发表时间：
2006-11-01
影响因子：
3.2
通讯作者：
Brown, Francis H.
中科院分区：
文献类型：
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作者：
Gathogo, Patrick N.;Brown, Francis H.
最近的地质研究表明，所有古人类和几乎所有其他已发表的哺乳动物化石都来自Koobi Fora的古生物收藏区123。来自KBS凝灰岩（1.87 +/- 0.02 Ma）和Lower Ileret凝灰岩（1.53 +/- 0.01 Ma）之间的水平。更具体地说，这些化石来自下伊勒雷特凝灰岩下方53米的剖面，在这个区间，床层横向变化明显，特别是那些含有软体动物和藻类叠层石的单元。Burgi上段（类似于2.00-1.87 Ma）仅在123区的西南部出现。邻近的110区包含较大的成员暴露，在那里，KBS凝灰岩被保存为湖相沉积物中的气落火山灰，也被保存为河流再沉积的火山灰。我们在123区这一段没有发现原位哺乳动物化石，但在一些专题研究中记录了表面标本。在20世纪70年代发现的123地区的古人类化石被认为是KBS凝灰岩之上的地层，但后来被认为是KBS凝灰岩（现在被称为上Burgi段）之下的地层。这项研究明确地将123区人类定位在KBS成员中。这些古人类的年龄大多在1.60至1.65亿元之间，但最年轻的可能只有1.53亿元，最古老的可能只有1.75亿元。所有人的年龄都比先前估计的年轻0.15-0.30兆当量。新的时代估计，结合已发表的化石分类归属，表明至少有两种人属与古猿一起在该地区共存，直到至少1.65 Ma。对KNM-ER 1813和KNM-ER 1470头骨的比较，被认为是年龄相当的，是关于“感觉能人”是否实际上由能人和鲁道夫人两个物种组成的争论的焦点。这两个颅骨在时间上的间隔大约为0.25 myr，因此，关于它们同一性的争论不再需要面对单个物种内异常高的同期变异问题。(c) 2006 Elsevier Ltd.所有航班预订。
Recent geologic study shows that all hominins and nearly all other published mammalian fossils from Paleontological Collection Area 123, Koobi Fora. Kenya, derive from levels between the KBS Tuff (1.87 +/- 0.02 Ma) and the Lower Ileret Tuff (1.53 +/- 0.01 Ma). More specifically, the fossils derive from 53 m of section below the Lower Ileret Tuff, an interval in which beds vary markedly laterally, especially those units containing molluscs and algal stromatolites. The upper Burgi Member (similar to 2.00-1.87 Ma) crops out only in the southwestern part of Area 123. Adjacent Area 110 contains larger exposures of the member, and there the KBS Tuff is preserved as an airfall ash in lacustrine deposits and also as a fluvially redeposited ash. We observed no mammalian fossils in situ in this member in Area 123, but surface specimens have been documented in some monographic treatments.Fossil hominins from Area 123 were attributed to strata above the KBS Tuff in the 1970s, but later they were assigned to strata below the KBS Tuff (now called the upper Burgi Member). This study definitively places the Area 123 hominins in the KBS Member. Most of these hominins are between 1.60 and 1.65 myr in age, but the youngest may date to only 1.53 Ma, and the oldest, to 1.75 Ma. All are 0.15-0.30 myr younger than previously estimated. The new age estimates, in conjunction with published taxonomic attributions of fossils, suggest that at least two species of Homo coexisted in the region along with A. boisei until at least 1.65 Ma. Comparison of crania KNM-ER 1813 and KNM-ER 1470, which were believed to be of comparable age, is at the focus of the debate over whether Homo habilis sensu lato is in fact composed of two species: Homo habilis and Homo rudolfensis. These two crania are separated in time by similar to 0.25 myr, and therefore, arguments for their conspecificity no longer need to confront the issue of unusually high contemporaneous variation within a single species. (c) 2006 Elsevier Ltd. All fights reserved.