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Laetoli Pliocene Paleoecology: A reanalysis via morphological and behavioral approaches
Introduction
Paleoanthropologists have established that human bipedal gait evolved within the savanna-like environments about 4 million years ago, and the fossil footprints discovered at Laetoli in 1974 by Dr. Mary Leakey reinforced this idea. Attempted studies to construct the environments in which human progenitors (the hominids) lived have in general produced models that favor the savanna-like habitats. Of particular interest is the proposed ecological model for the Laetoli bipeds by Leakey et. al. (1987), which suggest that open country savanna landscape similar to modern environments of the Serengeti Plains characterized the ancient landscape at Laetoli. However, based on data from fossil fauna composition, stratigraphic, and taphonomic evidence from Laetoli, it is much more evident that as the only upland Pliocene site in East Africa, Laetoli was characterized by a complex mosaic environment much different from the currently proposed open country savanna model. Therefore, the current ecological interpretation of the Laetoli environments not only provide a misleading picture of the ancient Laetoli but also provide limited knowledge on how human ancestors exploited the ancient landscape. The interpretation provided from the current ecological models do not help to answer critical questions such as: What role did the savanna-like environment influence the evolution of upright posture in humans? Or simply, is the adaptation of bipedal gait in humans a result of changing environments during the Pliocene period and, if so, what kinds of environments did our ancestors live in?In order to answer the questions related to the origin and causes of upright posture in humans, we need to understand the past environments. Therefore, the study "Laetoli Pliocene Paleoecology: A reanalysis via morphological and behavioral approaches" was an attempt to model Laetoli Pliocene environments using functional, morphological, and behavioral variables of bovid limb morphology as they relate to various locomotor patterns. The study took into account taphonomic and stratigraphic information that helped to produce a holistic model of the Laetoli Pliocene paleoenvironments.
Importance of Laetoli as a Paleoanthropological Site
The uniqueness of Laetoli as an ecologically significant Pliocene upland site in eastern Africa makes it particularly well suited for paleoenvironmental analysis. Its paleobiota points toward an environmental setting without major rivers or nearby lakes. Laetoli differs from other African Pliocene sites such as Aramis and Hadar in the Awash Valley (Ethiopia); Kanapoi, Lothagam, and Koobi Fora in the Gregory Rift Valley (Kenya); and Makapansgat Lime Works and Kromdraai (South Africa). These sites are either of fluviatile, lacustrine or alluvial origin unlike Laetoli, which is entirely an upland site. Likewise, Laetoli vertebrate fossil fauna is also of great interest because the taxonomic composition is different from other East African fauna of comparable age. Most remarkably also are the Footprint Tuffs at Laetoli, in which tracks and trails of a great variety of animals, many long extinct, are well preserved (Leakey, 1987).Laetoli deposits consist almost entirely of land-laid, eolian, and water-worked tuffs. Of particular interest to paleoenvironmental study conducted are the Laetolil Beds, where numerous faunal remains, including hominids, have been recovered. The stratigraphic component of the study focused on the Upper Unit of the Laetolil Beds, because of the abundant fossil remains recovered within this sequence. In addition, Tuff 7 in the Upper Laetolil Beds (also known as the footprint tuff) has produced well-preserved animal and hominid footprint trails that have been geochemically dated to 3.5 million years old (Curtis and Drake, 1987).
References
Drake, R. and Curtis, G.H. (1987). Geochronology of the Laetoli Fossil
Localities. In M.D. Leakey
and J.M. Harris (eds.), Laetoli: A Pliocene Site in Northern Tanzania. Oxford: Clarendon Press, pp. 48-52.
Leakey, M.D. (1987). The Hominid Footprints: Introduction. In M.D. Leakey and J.M. Harris (eds.), Laetoli: A Pliocene Site in Northern Tanzania. Oxford: Clarendon Press, pp. 490-496.
Leakey, M.D., Beden, M., Guérin, C., Renders, E.M. and Sondaar, P. (1987). Animal prints and trails. In M.D. Leakey and J.M. Harris (eds.), Laetoli: A Pliocene Site in Northern Tanzania. Oxford: Clarendon Press, pp.451-489.
