An international multi-disciplinary team of scientists have determined that a well-known group of early Homo (early human) fossils discovered in previous investigations at Koobi Fora in the Turkana Basin of East Africa have an age range that is older than previously estimated.
Led by archaeologist Josephine C.A. Joordens of the Netherlands’ Leiden University, the researchers combined magnetostratigraphy and strontium (Sr) isotope stratigraphy techniques to develop a new age constraint range for 15 selected hominin fossils found in deposits on the Karari Ridge of the Koobi Fora region in the eastern Turkana Basin (Kenya). Magnetostratigraphy measures the polarity of Earth’s changing magnetic field at the time a stratum (layer) was deposited. Strontium isotope stratigraphy involves measuring the ratios of Strontium isotopes in sediments to determine relative ages between successively deposited sediments. The fossils included key specimens such as cranium KNM-ER 1470, partial face KNM-ER 62000 and mandibles KNM-ER 1482, KNM-ER 1801, and KNM-ER 1802, all well-known among scientists and scholars involved in human evolution research. The fossil KNM-ER 1470, for example, has been classified as belonging to the early human species Homo rudolfensis, discovered by Bernard Ngeneo in 1972 and considered a possible theoretical contender for being ancestral to the human line. It has been dated to about 1.9 million years BPE.
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Satellite view of the Turkana Basin, Koobi Fora region, showing Lake Turkana. Fossils were found in an area just east of Lake Turkana. Wikimedia Commons
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Surface level view of Turkana Basin looking toward Lake Turkana. AdamPG, Wikimedia Commons
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Now, however, the results of their tests and analyses show a new age-range constraint of between 1.945 ± 0.004 and 2.058 ± 0.034 Ma, making the fossil finds older than previously estimated, and providing a sharper, more specific age range for their deposit.
“To address questions regarding the evolutionary origin, radiation and dispersal of the genus Homo,” writes Joorden, et al. in their report, “it is crucial to be able to place the occurrence of hominin fossils in a high-resolution chronological framework. The period around 2 Ma (millions of years ago) in eastern Africa is of particular interest as it is at this time that a more substantial fossil record of the genus Homo is first found.”
In addition to the new age range, their research shed light on the possible geographic origins and ecological/climatological adaptability of these early humans. As they report:
“……..our results show that in this time interval, hominins occurred throughout the wet–dry climate cycles, supporting the hypothesis that the lacustrine Turkana Basin was a refugium during regionally dry periods. By establishing the observed first appearance datum of a marine-derived stingray in UBU [upper Burgi] deposits at 2.058 ± 0.034 Ma, we show that at this time the Turkana Basin was hydrographically connected [via a postulated ancient ‘Turkana River’] to the Indian Ocean, facilitating dispersal of fauna between these areas. From a biogeographical perspective, we propose that the Indian Ocean coastal strip should be considered as a possible source area for one or more of the multiple Homo species in the Turkana Basin from over 2 Ma onwards.”
The study report, Improved age control on early Homo fossils from the upper Burgi Member at Koobi Fora, Kenya, has been published in the December 2013 issue of the Journal of Human Evolution.
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Cover photo, Top Left: Homo rudolfensis skull (KNM ER 1470) reconstruction displayed at Museum of Man, San Diego. Durova, Wikimedia Commons
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