Stable isotope-based diet reconstructions of Turkana Basin hominins

Abstract

Hominin fossil evidence in the Turkana Basin in Kenya from ca . 4.1 to 1.4 Ma samples two archaic early hominin genera and records some of the early evolutionary history of Paranthropus and Homo . Stable carbon isotopes in fossil tooth enamel are used to estimate the fraction of diet derived from C 3 or C 4 resources in these hominin taxa. The earliest hominin species in the Turkana Basin, Australopithecus anamensis , derived nearly all of its diet from C 3 resources. Subsequently, by ca . 3.3 Ma, the later Kenyanthropus platyops had a very wide dietary range—from virtually a purely C 3 resource-based diet to one dominated by C 4 resources. By ca . 2 Ma, hominins in the Turkana Basin had split into two distinct groups: specimens attributable to the genus Homo provide evidence for a diet with a ca . 65/35 ratio of C 3 - to C 4 -based resources, whereas P. boisei had a higher fraction of C 4 -based diet ( ca . 25/75 ratio). Homo sp. increased the fraction of C 4 -based resources in the diet through ca . 1.5 Ma, whereas P. boisei maintained its high dependency on C 4 -derived resources.

Stable isotopes serving as a checkpoint

“…Levin et al (4) found the isotopic composition of many mammalian taxa from Woranso-Mille to be in accordance with both field observations and previously reported data, in which giraffes, on one hand, and Alcelaphines and other presumed grass grazers, on the other hand, consistently occupied the two end points of the mammalian carbon isotopic spectrum (C 3 -and C 4 -dominated). Such observations confirm suggestions that diagenesis is not playing any obvious role in the carbon isotopic composition of wellselected tooth enamel (11,12) (Fig. 1A).…”

“…What is more, the conclusions of Levin et al (4) are consistent with the recently published eastern African stable isotopic dataset (11)(12)(13). These papers had already presented tantalizing evidence that separated Australopithecus afarensis from Australopithecus anamensis based on their carbon isotopic composition, despite their morphological similarities (Fig.…”

“…The first isotopic study on eastern African fossils from Tanzania showed that P. boisei and Homo had very different diets (10), and it was followed by other work concluding that the former species' diet included more C 4 food (up to 80%) than the diet of any other known hominin taxon (8). More recently, isotopic studies were expanded to larger eastern African datasets and took our knowledge of hominin diet to a different level in terms of depth and temporal extent (11)(12)(13). This compilation identified key dietary transitions in the hominin lineage and established patterns and major trends across taxa, allowing for a synthesis of the state of our knowledge today (13) (Fig.…”

Diet of Theropithecus from 4 to 1 Ma in Kenya

“…Tooth enamel from modern baboons from Africa, including P. anubis and P. hamadryas, have an average δ 13 C 1750 value of −10.2 ± 2.7‰ (n = 36; maximum = −2.5‰; minimum = −15.5‰) (data in ref. 28), corresponding to a ca. 15 ± 20% C 4 -based diet; the diets of modern baboons are very different from T. brumpti or T. oswaldi ( Fig.…”

“…We discuss Theropithecus in the context of C 3 -and C 4 -derived diet resources and the overall context of isotope ecology in the Turkana Basin. The diet of Theropithecus is of interest compared with the diets of early hominins (26,28) from the same deposits; hominins exhibit a change in the use of C 4 resources over this time interval, and thus, these primates were in potential competition for dietary resources.…”