Dietary changes of large herbivores in the Turkana Basin, Kenya from 4 to 1 Ma

Abstract

A large stable isotope dataset from East and Central Africa from ca. 30 regional collection sites that range from forest to grassland shows that most extant East and Central African large herbivore taxa have diets dominated by C4 grazing or C3 browsing. Comparison with the fossil record shows that faunal assemblages from ca. 4.1–2.35 Ma in the Turkana Basin had a greater diversity of C3–C4 mixed feeding taxa than is presently found in modern East and Central African environments. In contrast, the period from 2.35 to 1.0 Ma had more C4-grazing taxa, especially nonruminant C4-grazing taxa, than are found in modern environments in East and Central Africa. Many nonbovid C4 grazers became extinct in Africa, notably the suid Notochoerus, the hipparion equid Eurygnathohippus, the giraffid Sivatherium, and the elephantid Elephas. Other important nonruminant C4-grazing taxa switched to browsing, including suids in the lineage Kolpochoerus-Hylochoerus and the elephant Loxodonta. Many modern herbivore taxa in Africa have diets that differ significantly from their fossil relatives. Elephants and tragelaphin bovids are two groups often used for paleoecological insight, yet their fossil diets were very different from their modern closest relatives; therefore, their taxonomic presence in a fossil assemblage does not indicate they had a similar ecological function in the past as they do at present. Overall, we find ecological assemblages of C3-browsing, C3–C4-mixed feeding, and C4-grazing taxa in the Turkana Basin fossil record that are different from any modern ecosystem in East or Central Africa.

Aridity and hominin environments

“…5). These correlations are weak, however, and during the Pliocene-Pleistocene forests were rare in the Turkana Basin (25,27,49,58) and elsewhere in eastern Africa (23). After excluding forests, we find no relationship between WD and the proportional abundance of each diet guild (Fig.…”

“…Increasing aridity has been thought to drive the origin and subsequent expansion of C 4 plants (grasses and sedges) (22). The long-term increase in the abundance of C 4 plants throughout the Pliocene and Pleistocene has been well documented in eastern Africa using carbon isotope ratios in pedogenic carbonates and leaf wax biomarkers (23,24) and coincides with an increasing reliance on C 4 -based resources among mammals, including hominins and other primates (25,26). Variation in the timing of vegetation change across basins indicates that existing continental-and regional-scale climate records are not sufficient to understand the drivers of basin-and local-scale ecological change, and do not reflect local hominin environments (23,27).…”

“…Owing to the lack of suitable fossil collections for the application of our tooth enamel aridity proxy, we do not address climate before ∼4 Ma. The Late Miocene appears to have been more humid in Turkana and elsewhere (34), although aridification before ∼4 Ma predates the long-term increase in C 4 vegetation and C 4 grazing mammalian herbivore that continued throughout the Pliocene and Pleistocene (25,27).…”

In Rift Valley settings with a feedback loop, assortative mating for versatility predicts hominin brain enlargement in some detail

“…Why might enlargement start just then, after millions of years of little growth while the Pliocene climate cooled? The number of large-grazer taxa at Turkana in the Rift Valley doubled between -2.50 myr and -2.35 myr (Cerling et al, 2015). In that same 150 kyr period (Fig.…”

Understanding specifics in generalist diets of carnivorans by analyzing stable carbon isotope values in Pleistocene mammals of Florida

“…African grasses evolved under pressure of herbivory from large mammals (Stuart-Hill and Mentis 1982;Coughenour 1985;Cerling et al 2015) and there is evidence of enhanced productivity when subjected to repetitive grazing (McNaughton 1979;Wallace et al 1985;Simoes and Baruch 1991). In addition, they are adapted to a wide range of abiotic conditions (Baruch 1994), and considered to be more palatable and nutritious than native North American grasses (Parsons 1972;Baruch 1994;Brown and Kalmbacher 1998).…”