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Objectives: Australopithecus anamensis has comparable δ13Cenamel values to Ardipithecus ramidus, and both have been characterized as C3 feeders in open woodland habitats similar to "savanna" chimps. Unlike Ar. ramidus and "savanna" chimps, A. anamensis shows a derived dentognathic morphology for tough foods and a dental microwear pattern similar to the C3–C4‐mixed‐feeding A. afarensis. Here I test the hypothesis that changing the variables (ε*enamel‐diet, δ13CC3, δ13CC4 values) used to calculate the percentage of dietary C4 foods (%C4 diet) by 1–2‰ does not make a substantial difference for hominin diet reconstructions [van der Merwe, Masao, & Bamford, 2008, South African Journal of Science 104:153–155]. Materials and Methods: I estimate vegetation structures for A. anamensis with pedogenic carbonate and faunal enamel δ13C values from the Pliocene Omo‐Turkana Basin (4.2–3.9 Ma). I recalculate A. anamensis' %C4 diet based on new body size‐dependent estimates of the ε*enamel‐diet value and alternative δ13CC3 and δ13CC4 values. Results: The Pliocene Omo‐Turkana Basin shows evidence for dietary resources with a wide range of δ13C values including canopy‐driven 13C depleted ground C3 foods. Alternative equation variables changed by 1–2‰ yield higher C4 estimates for A. anamensis (15–31%) than previously thought (0–10%). The choice of δ13CC3 and δ13CC4 values for estimating %C4 is not a perfunctory task and potentially explains the δ13C isotopic equifinality of A. anamensis and "savanna" chimps. Discussion: My integrative diet model reconciles the carbon isotopic data with the dentognathic and microwear evidence of A. anamensis' diet and suggests that "savanna" chimps are not proper dietary analogs of A. anamensis. A foraging strategy across heterogeneous habitats of the Pliocene Omo‐Turkana Basin incorporating an array of 13C‐depleted and 13C‐enriched C3 foods and a portion of C4 resources may have served as one of the selective pressures for A. anamensis, the earliest habitual biped [van der Merwe et al., 2008, South African Journal of Science 104:153–155]. [ABSTRACT FROM AUTHOR]

Determining the diet of an extinct species is paramount in any attempt to reconstruct its paleoecology. Because the distribution and mechanical properties of food items may impact postcranial, cranial, mandibular, and dental morphologies related to their procurement, ingestion, and mastication, these anatomical attributes have been studied intensively. However, while mechanical environments influence skeletal and dental features, it is not clear to what extent they dictate particular morphologies. Although biomechanical explanations have been widely applied to extinct hominins in attempts to retrodict dietary proclivities, morphology may say as much about what they were capable of eating, and perhaps more about phylogenetic history, than about the nature of the diet. Anatomical attributes may establish boundary limits, but direct evidence left by the foods that were actually (rather than hypothetically) consumed is required to reconstruct diet. Dental microwear and the stable light isotope chemistry of tooth enamel provide such evidence, and are especially powerful when used in tandem. We review the foundations for microwear and biogeochemistry in diet reconstruction, and discuss this evidence for six early hominin species ( Ardipithecus ramidus, Australopithecus anamensis, Au. afarensis, Au. africanus, Paranthropus robustus, and P. boisei). The dietary signals derived from microwear and isotope chemistry are sometimes at odds with inferences from biomechanical approaches, a potentially disquieting conundrum that is particularly evident for several species. Am J Phys Anthropol 148:285-317, 2012. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The phylogenetic relationship between Australopithecus anamensis and Australopithecus afarensis has been hypothesized as ancestor-descendant. However, the weakest part of this hypothesis has been the absence of fossil samples between 3.6 and 3.9 million years ago. Here we describe new fossil specimens from the Woranso-Mille site in Ethiopia that are directly relevant to this issue. They derive from sediments chronometrically dated to 3.57-3.8 million years ago. The new fossil specimens are largely isolated teeth, partial mandibles, and maxillae, and some postcranial fragments. However, they shed some light on the relationships between Au. anamensis and Au. afarensis. The dental morphology shows closer affinity with Au. anamensis from Allia BayfKanapoi (Kenya) and Asa Issie (Ethiopia) than with Au. afarensis from Hadar (Ethiopia). However, they are intermediate in dental and mandibular morphology between Au. anamensis and the older Au. afarensis material from Laetoli. The new fossils lend strong support to the hypothesized ancestor-descendant relationship between these two early Australopithecus species. The Woranso-Mille hominids cannot be unequivocally assigned to either taxon due to their dental morphological intermediacy. This could be an indication that the Kanapoi, Allia Bay, and Asa Issie Au. anamensis is the primitive form of Au. afarensis at Hadar with the Laetoli and Woranso-Mille populations sampling a mosaic of morphological features from both ends. It is particularly difficult to draw a line between Au. anamensis and Au. afarensis in light of the new discoveries from Woranso-Mille. The morphology provides no evidence that Au. afarensis and Au. anamensis represent distinct taxa. [ABSTRACT FROM AUTHOR]