Calcium isotopic ecology of Turkana Basin hominins

Abstract

Diet is a major driver of hominin evolution, but most of the geochemical evidence relies on carbon isotopes (δ 13 C). Here, we report enamel stable calcium isotope (δ 44/42 Ca) values against δ 13 C values for several hominins and co-existing primates in the Turkana Basin area, circa 4 to 2 Ma. Australopithecus anamensis clusters with mammal browsers, Kenyanthropus platyops is distinct from A. anamensis in foraging into more open environments and the coexisting Theropithecus brumpti encompasses both the grazer and omnivore/carnivore domains. Early Homo is remarkable for its wide distribution in δ 44/42 Ca values, possibly reflecting omnivorous and opportunistic preferences. Paranthropus boisei is uniquely distributed in the δ 13 C versus δ 44/42 Ca iso-space being distinct from all other hominins from the Turkana Basin area as well as from the co-existing Theropithecus oswaldi. Several hypotheses are explored to discuss the unique δ 44/42 Ca values of Paranthropus boisei including significant differences observed with δ 44/42 Ca values recently reported for P. robustus from South Africa, questioning the monophyly of this genus.

Contracting eastern African C4 grasslands during the extinction of Paranthropus boisei

“…1 C). Ungulate C 4 -grazer meat and marrow may have been the primary source of H. erectus’ C 4 diet 13 , 63 , supporting the interpretation of niche separation rather than direct competition between the hominin sister taxa even after 1.65 Ma. But notably a few Homo specimens approach P. boisei’s δ 13 C enamel and δ 44/42 Ca enamel values 13 , which could be interpreted to indicate that segments of the omnivorous Homo populations exploited some resources within P. boisei’s dietary niche 12 .…”

“…Eastern African hominins and Theropithecus , the large-bodied baboon, underwent a dietary transition incorporating more C 4 foods in the early Pleistocene 6 , 8 , 9 , 12 , which have been attributed to behavioral changes in response to complex competitive landscapes 12 . Distinct from other Pleistocene hominins, P. boisei , the last eastern African paranthropine species, yielded δ 13 C enamel and δ 44/42 Ca enamel values indicating a herbivorous 13 and primarily C 4 diet 6 from ~ 2.3 Ma until its last appearance from the fossil record at ~ 1.3 Ma 14 . Unexpectedly, isotopic evidence for this shift into a C 4 -plant feeding niche was not mirrored by changes in microwear patterns or dentognathic morphology 7 , 10 , 15 .…”

“…More recent archaeological evidence suggests that both Homo and Paranthropus were plausible inheritors of tool-making behaviors 4 , 5 , and stable carbon isotopic (δ 13 C enamel ) and microwear analyses of fossil specimens have revealed a dynamic and complex evolutionary history of Pleistocene African hominin and non-hominin primate diets (Fig. 1 ) 6 – 13 . Eastern African hominins and Theropithecus , the large-bodied baboon, underwent a dietary transition incorporating more C 4 foods in the early Pleistocene 6 , 8 , 9 , 12 , which have been attributed to behavioral changes in response to complex competitive landscapes 12 .…”

“…Wood and Patterson (2020) 16 suggested that P. boisei’s 1-myr morphological and dietary stasis signifies that its occupied niche and associated adaptations were “remarkably durable.” Although eastern African hominins may have begun their evolutionary trajectories as C 3 -C 4 -mixed-feeding opportunists during the early Pleistocene 11 , P. boisei evolved to be a C 4 plant specialist 13 sharing more dietary similarities to T. oswaldi than with members of genus Homo , who remained C 3 -C 4 -mixed feeding omnivores (Fig. 1 A–C).…”

“…2 A–C), from 1.4 to 0.7 Ma, an under-sampled interval for pedogenic carbonates in an otherwise well-studied region of human evolutionary environments (see " Methods ", " Supplementary Information "). The Turkana region is the most fossiliferous of the known P. boisei sites 18 , and Turkana specimens constitute the majority of isotopically analyzed P. boisei enamel samples to date 6 , 8 , 12 , 13 . We combine our new δ 13 C PC data to those from other EARS locations preserving the MPT interval, calculate fraction of woody canopy cover (ƒ WC ) 24 , and compare the EARS ƒ WC record to other environmental, ecological and climatic proxy records from 3 to 0 Ma to examine the contexts of P. boisei’s extinction.…”