Late Miocene to Pliocene carbon isotope record of differential diet change among East African herbivores

Abstract

Stable isotope and molecular data suggest that C 4 grasses first appeared globally in the Oligocene. In East Africa, stable isotope data from pedogenic carbonate and fossil tooth enamel suggest a first appearance between 15-10 Ma and subsequent expansion during the Plio-Pleistocene. The fossil enamel record has the potential to provide detailed information about the rates of dietary adaptation to this new resource among different herbivore lineages. We present carbon isotope data from 452 fossil teeth that record differential rates of diet change from C 3 to mixed C 3 /C 4 or C 4 diets among East African herbivore families at seven different time periods during the Late Miocene to the Pliocene (9.9-3.2 Ma). Significant amounts of C 4 grasses were present in equid diets beginning at 9.9 Ma and in rhinocerotid diets by 9.6 Ma, although there is no isotopic evidence for expansive C 4 grasslands in this part of the Late Miocene. Bovids and hippopotamids followed suit with individuals that had C 4 -dominated (>65%) diets by 7.4 Ma. Suids adopted C 4 -dominated diets between 6.5 and 4.2 Ma. Gomphotheriids and elephantids had mostly C 3 -dominated diets through 9.3 Ma, but became dedicated C 4 grazers by 6.5 Ma. Deinotheriids and giraffids maintained a predominantly C 3 diet throughout the record. The sequence of differential diet change among herbivore lineages provides ecological insight into a key period of hominid evolution and valuable information for future studies that focus on morphological changes associated with diet change.carbon isotopes | herbivore diet | bioapatite | paleodiet | mammal

Stable carbon isotopes and human evolution

“…However, if the 13 C/ 12 C ratio shifts over long intervals in the teeth of species that were almost certainly grazers, a reasonable inference is that there was a shift in the nature of the available grass. Thus, an increase in 13 C enrichment in grazer enamel across multiple lineages implies that C 4 grasses spread at the expense of C 3 plants in tropical and subtropical latitudes between 8 and 3 Ma (4,5). This is paleoanthropologically significant, because it supports the "savanna hypothesis," according to which hominin bipedalism represents an adaptive response to the increasingly patchy distribution of trees or tree stands vs. grasses in tropical and subtropical Africa beginning roughly 8 Ma.…”

Stable isotope-based diet reconstructions of Turkana Basin hominins

“…The only alternative is a diet based on meat/insect resources based on animals that themselves consume almost entirely C 3 resources. However, note that initial surveys of fossil mammals from the Turkana region show that, by 7 Ma and on, most herbivores in the Turkana Basin had C 4 -based diets (10,11,46,47). Thus, Au.…”

“…Tropical grasses were rare until the late Miocene, when they greatly expanded in abundance; therefore, by the latest Miocene and Pliocene, many mammals had changed their diets, and some had become dependent on this relatively new dietary resource (10,11). The study of this dietary evolution is based on the difference in carbon isotope ratios of plants that use either the C 3 or C 4 photosynthetic pathway (12).…”

Diet of Theropithecus from 4 to 1 Ma in Kenya

“…Stable isotope ratios of 13 C/ 12 C are ideally suited to test this hypothesis because of the difference in isotope ratios between C 3 plants (most dicots) and C 4 plants (grasses and sedges, both of which are monocots) in the tropics; the dietary distinction between C 3 and C 4 plant-derived foods is preserved in the fossil record of Africa for most of the past 10 Ma (14,15). The δ 13 C values of tooth enamel from modern and fossil browsers are about −12‰ in open forests through grasslands, whereas grazers have δ 13 C values near 2‰, and mixed feeders have intermediate values (16)(17)(18)(19).…”