Introduction: The Laetoli Hominins and Associated Fauna

Laetoli in northern Tanzania is one of the most important paleontological and paleoanthropological localities in Africa. In addition to fossil hominins, there is a diverse associated fauna. The Laetoli fauna is important because it serves as a key comparative reference for other Plio-Pleistocene sites in Africa, it samples several time periods that are generally poorly represented at other paleontological sites in East Africa, and it provides key insights into the faunal and floral diversity during the Pliocene. As a result of renewed fieldwork at Laetoli (1998–2005) more than 25,000 fossils have been collected, of which more than half are fossil mammals. Most of the fossils were recovered from the Upper Laetolil Beds (3.6–3.85 Ma), but smaller samples came from the Lower Laetolil Beds (3.85–4.4 Ma) and Upper Ndolanya Beds (2.66 Ma). These include new specimens of Australopithecus afarensis from the Upper Laetolil Beds and the first finds of fossil hominins from the Upper Ndolanya Beds, attributable to Paranthropus aethiopicus. Inferences about the paleoecology at Laetoli are important for understanding the possible range of hominin habitat preferences and ecological change in East Africa during the Pliocene. The evidence from a wide range of analyses indicates that a mosaic of closed woodland, open woodland, shrubland and grassland dominated the paleoecology of the Upper Laetolil Beds. The region would have been dry for most of the year, except for the possible occurrence of permanent springs along the margin of the Eyasi Plateau and ephemeral pools and rivers during the rainy season. The paleoecological reconstruction of the Upper Ndolanya Beds is more problematic because of conflicting lines of evidence, but it is very likely that conditions were drier than in the Upper Laetolil Beds with a greater proportion of grassland, but that closed and open woodlands were still a major part of the ecosystem.