Diversity in Australopithecus T he fourth annual Stony Brook University Human Evolution Symposium, ‘‘Diversity in Aus- tralopithecus: Tracking the Earliest Bipeds,’’ was convened by Richard Leakey on September 25 th , 2007, at Stony Brook University. Following a brief introduction by Dr. Leakey (Stony Brook University), William Kimbel (Institute of Human Origins, Arizona State University) began the series of public presenta- tions by introducing and discussing the concept of a ‘‘lineage’’ and whether or not it may apply within the genus Australopithecus. Kimbel first described the diversity of austral- opithecine species currently known and then noted some commonalities of the group, many related to the increased robusticity of the dentition and masticatory apparatus. He also pointed out that anatomical features such as a gracile dentition and straight, flat face, features evident in the recently discovered Kenyanthro- pus platyops, are important character- istics that distinguish Kenyanthropus and other hominins from those usu- ally regarded as australopithecines. Kimbel eloquently argued that differ- ent lineages within australopithecines may be present and that recognition of these lineages, where they exist, would help clarify evolutionary rela- tionships among the various homi- nids living between about 4 and 2.5 million years ago. The next presentation, by Ron Clarke (University of Witswaters- rand), focused on the new hominin skeleton from the Silberberg Grotto within the Sterkfontein cave, a specimen more commonly known by its nickname, ‘‘Little Foot.’’ Ongoing excavations directed by Dr. Clarke and supported by the Paleo-Anthro- pology Scientific Trust, have recently uncovered even more of the skeleton, demonstrating that it is the most complete single specimen of Australo- pithecus yet discovered. This beauti- fully preserved specimen includes a nearly complete face and skull, much of the axial and appendicular skele- ton, and even complete feet and hands preserved in their anatomical position at death. The skeleton is truly amazing, and will no doubt provide a wealth of information regarding the locomotor behavior of Australopithe- cus, phylogenetic relationships among hominin taxa, the habitat preferences of australopithecines, and the number of Australopithecus species present at Sterkfontein. In the afternoon session, Meave Leakey (Stony Brook University) introduced her most recently discov- ered hominin, Kenyanthropous pla- tyops, dated to 3.5 million years ago, from the western region of Lake Tur- kana. Leakey described the temporal, ecological, and geological context of K. platyops and introduced several derived features of its craniodental morphology that differ from the fea- tures of contemporaneous A. afaren- sis and, in some ways, resemble Homo rudolfensis. For instance, re- sults of comparative analyses showed K. platyops to have a flatter midface, less subnasal prognathicism, and smaller molars, especially M 1 and M 2 , relative to A. anamensis, A. afarensis, A. africanus, or A. garhi. Also, the ma- lar region is taller and more vertically oriented, while the maxillary zygo- matic process is more anteriorly posi- tioned on K. platyops, suggesting a reconfiguration of the chewing appa- ratus. In overall appearance, Leakey felt that K. platyops is more similar in facial architecture to H. rudolfensis than to any species of Australopithe- cus or Paranthropus. Leakey con- cluded by recognizing the issue of sampling bias in the fossil record. She noted that hominin fossils are most likely to be deposited on flood plains and to be preserved during wet periods rather than periods of drying or seasonal drought. In conclusion, she urged researchers to take this bias into account when interpreting fossil assemblages. Matt Sponheimer (University of Colorado, Boulder) followed with an exciting presentation on the paleo- diets of Paranthropus and Australopi- thecus. Sponheimer introduced a new technique for assessing variabili- ty in hominin diets, laser ablation stable isotopic analysis, which meas- ures diet over a longer time than do traditional dental microwear analy- ses. He explained that hominins could specialize on C 3 foods such as soft leaves and fruit or they could specialize on C 4 foods such as grasses, seeds, sedges, tubers, or the animals that eat these foods. Alterna- tively, they could vary their diet according to seasonal or interannual changes in availability and switch between C 3 and C 4 foods, which would signal a more flexible strategy. Sponhemier presented results sug- gesting that A. afarensis is a narrow specialist across all parts of its range in east Africa, while Paranthropus robustus exhibits a more variable diet over time, relying largely on C 4 foods from the savanna but also shifting to C 3 items during certain periods. The variable pattern described for another South African hominin, A. africanus, appears to resemble the generalist strategy of P. robustus more than the specialist strategy of A. afarensis, suggesting a link among paleogeography, paleoe- cology, and dietary adaptation. Following Sponheimer, Kaye Reed (Institute of Human Origins, Arizona State University) discussed diversity in Australopithecus in relation to paleoecology. Paleoecology is impor- tant because many early models regarding hominin origins and the NEWS Evolutionary Anthropology 17:3–4 (2008)