Revisiting the pedogenic carbonate isotopes and paleoenvironmental interpretation of Kanapoi

Reconstructed habitats of Australopithecus anamensis at Kanapoi by Wynn (2000) yielded evidence for both wooded and grassy environments. Wynn's study was based on stable isotopic (δ¹³C_PC, δ¹⁸O_PC) analyses of a small sample of pedogenic nodules (n = 14) collected from paleosols spanning Kanapoi's stratigraphic interval. Whether this small sample size adequately characterized Kanapoi's vegetation or was the result of time averaging remains unclear. To address this uncertainty, we sampled Kanapoi paleosols at 39 locations (78 analyses) from laterally extensive units. Our data demonstrate that Kanapoi offered A. anamensis diverse habitats distributed in temporally discrete stratigraphic horizons. Habitat heterogeneity appears to have been a real aspect of Kanapoi paleoenvironments and not an artifact of Wynn's (2000) small sample size or time averaging. We suggest habitat heterogeneity was influenced by the location of Kanapoi at the confluence of fluvial, deltaic, and lacustrine depositional environments. We also compared Kanapoi's δ¹³C_PC and δ¹⁸O_PC values to those of other Pliocene hominin localities in eastern Africa dated to 4.5-3.7 Ma. Kanapoi's δ¹⁸O_PC values are significantly higher than most sites, potentially reflecting regional variability in water source δ¹⁸O values and/or more arid climatic conditions. Kanapoi's δ¹³C_PC values indicate significantly more woody cover than at all other sites except those in the Turkana Basin. Kanapoi provided A. anamensis with a wide range of C₃-C₄ resources as the C₄ biome spread across eastern Africa. [Wynn, J.G., 2000. Paleosols, stable carbon isotopes and paleoenvironmental interpretation of Kanapoi, Northern Kenya. J. Hum. Evol. 39, 411-432.].