Reassessment of the paleoenvironment and preservation of hominid fossils from Hadar, Ethiopia

Abstract

Samples of paleosols from locality AL-333, known for numerous specimens of Australopithecus afarensis, were analyzed in order to reconstruct the original soils and environment of burial of the associated fossil hominids. The bones were found in swale-like features, within the calcareous and coarse-grained basal portion of a paleosol. This is more like an assemblage of bones buried during a single depositional episode, such as a flood, than an assemblage accumulated on a soil over a long period of time by carnivores or other means of death. What killed the hominids remains unclear, but considering the association of originally disarticulated bones of such hydraulically distinct types as phalanges and maxillae, it is very likely that they died and partially rotted at or very near this site. The paleosols at AL-333, here named the Fo and Go clay paleosols, have calcareous rhizoconcretions, granular surface horizons, prismatic peds, and shallow calcareous nodules and stringers like soils now supporting grassy woodland in semiarid regions. Although this group of hominids was buried in streamside gallery woodland, there is evidence from Laetoli, Tanzania, that A. afarensis ventured out into open wooded grassland as well. Evidence for this should be sought from other paleosols at Hadar.

Eocene and Oligocene Paleosols of Central Oregon

“…Also recognizable in calcareous horizons of paleosols from the Painted Hills is variation similar to sequences of development in time from diffuse carbonate to small and then large nodules, as observed in desert soils of different age (Gile et al, 1966(Gile et al, , 1981Machette, 1985). Some of the nodules encrust or enclose fossil bones that may have nucleated nodule growth, as in the Oligocene Brule Formation of South Dakota (Retallack, 1983), Miocene Sucker Creek Formation of Oregon (Downing and Park, 1998), and the Pliocene Hadar Formation of Ethiopia (Radosevich et al, 1992). Local fluctuation in groundwater chemistry similar to soil formation best explains such nucleation around bones (Downing and Park, 1998).…”

Hominid lifestyle and diet reconsidered: paleo-environmental and comparative data

“…Hadar, Afar Locality: 'Generally, the sediments represent lacustrine, lake margin, and associated fluvial deposits related to an extensive lake that periodically filled the entire basin' (Johanson et al, 1982) 9 Hadar AL.333 A. afarensis: 'The bones were found in swale-like features [...] it is very likely that they died and partially rotted at or very near this site [...] this group of hominids was buried in streamside gallery woodland' (Radosevich et al, 1992). 9 Hadar AL.288 gracile A. afarensis: Lucy lay in a small, slow moving stream.…”

Dynamic landscapes and human dispersal patterns: tectonics, coastlines, and the reconstruction of human habitats

“…Habitat reconstructions based on the analysis of sediments demonstrate that a range of vegetation types was probably present during the time of hominin occupation, including, swamps, seasonal (Manighetti et al, 2001;Rowland et al, 2007;Ayele et al, 2007). pans or 'playas', and more closed, wooded regions (Johanson et al, 1982;Kalb, Jolly et al, 1982;Radosevich et al, 1992;WoldeGabriel, et al, 1994WoldeGabriel, et al, , 2001Semaw et al, 2005). However, the relationship of these features to the original topography is difficult to establish in the present-day landscape because of the substantial changes that have been caused by active rifting over the past 2 Ma.…”