Evidence for a Late Pliocene faunal transition based on a new rodent assemblage from Oldowan locality Hadar A.L. 894, Afar Region, Ethiopia

The time interval between 3 Ma and 2 Ma marks several important transitions in human evolution, including the extinction of Australopithecus afarensis, the origin of the genus Homo, and the appearance of concentrated stone tool assemblages forming recognizable archaeological sites. The period also marks important changes in Earth’s climatic history, with the onset of northern hemisphere glaciation starting sometime between 2.8 Ma and 2.5 Ma, and it remains an unresolved question in paleoanthropology whether or not the global climatic events influenced in whole or in part, local terrestrial paleoenvironments in Africa and, through this, the course of human evolution.Changes in the terrestrial mammalian faunas of East Africa during this time interval are an important source of data about terrestrial paleoenvironments, and it has been argued that during this time period the mammalian faunas of Africa experienced a sudden pulse in the extinction and origination of taxa. The data corroborating this Turnover Pulse Hypothesis derive from both large mammal and micromammal data, though the fossil record of the former is much more abundant in this interval. New micromammal fossils recovered from ca. 2.4 Ma deposits at locality A.L. 894, low in the Busidima Formation in the Hadar study area of the Afar region, Ethiopia, reveal a significant faunal turnover when compared with previously published material from older 3.2 Ma micromammal assemblages from the Hadar Formation deposits. The results support the hypothesis of a major faunal transition, but larger sample sizes and more extensive temporal sampling are needed to refine the time and rate of change within this interval at Hadar.