Isotopic equifinality and rethinking the diet of Australopithecus anamensis

Abstract

Abstract 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].

Cite this work

No public copy is stored for this record, so only the metadata is cited.

Stored only when both papers are in the corpus — 26 citations exist upstream.

Papers that cite the same references — the relational fallback while embeddings are still backfilling.