Calcium isotopic patterns in enamel reflect different nursing behaviors among South African early hominins

Abstract

Nursing is pivotal in the social and biological evolution of hominins, but to date, early-life behavior among hominin lineages is a matter of debate. The calcium isotopic compositions (δ44/42Ca) of tooth enamel can provide dietary information on this period. Here, we measure the δ44/42Ca values in spatially located microsized regions in tooth enamel of 37 South African hominins to reconstruct early-life dietary-specific variability in Australopithecus africanus, Paranthropus robustus, and early Homo. Very low δ44/42Ca values (<−1.4‰), indicative of milk consumption, are measured in early Homo but not in A. africanus and P. robustus. In these latter taxa, transitional or adult nonmilk foods must have been provided in substantial quantities relative to breast milk rapidly after birth. The results suggest that early Homo have continued a predominantly breast milk–based nursing period for longer than A. africanus and P. robustus and have consequently more prolonged interbirth interval.

Calcium isotopic ecology of Turkana Basin hominins

“…Gorillas could be viewed as a remote plant-eating analogue. The two lateforming modern western lowland gorilla teeth from La Lopé in Gabon display calcium isotope values around −1.05‰ (Supplementary Data 1) 33 , comparable with the values of P. boisei. Although those gorillas feed on fruits, leaves, and ants, these resources arise from C 3 , not C 4 plants 11 .…”

“…3). Interestingly, P. robustus and A. africanus do not differ in δ 13 C values 9 , nor do they differ in δ 44/42 Ca values 33 (Fig. 3).…”

“…Whatever the exact dietary component or physiological specificity of P. boisei was, this species remains remarkable for exhibiting 44 Ca-enriched tooth enamel within a narrow range of isotope values, which most likely reflect a specialized diet on items with low isotopic variability 48 possibly associated to a physiology different than other primates. The range of calcium isotope values of P. boisei not only differs from other hominins of the Turkana Basin, it also differs from that of its South African congener P. robustus, which shows lower calcium isotope values 33 (Fig. 3).…”

“…3). P. robustus was interpreted to have had a flexible diet together with the contemporaneous early Homo from South Africa 9,49 , a hypothesis that seems corroborated by the overlap of calcium isotope values of P. robustus with early Homo and A. africanus 33 . From our study as well as previous ones based on δ 13 C values 1 or tooth microwear 21 , the emerging picture could be that of P. boisei in East Africa with a specialized diet versus P. robustus in South Africa with a flexible diet 9,49 .…”

“…Ca isotopic variability in modern Gorilla teeth. Teeth belonging to four modern western lowland gorilla (Gorilla gorilla gorilla) individuals from La Lopé National Park, Gabon, analyzed for Ca isotopes 33 , are presented here as a comparison with other hominin and non-hominin primates ( Fig. 1 teeth were formed early and include an incisor (G72) with a distinctly low δ 44/42 Ca value as well as a first molar (G39) with a surprisingly high δ 44/42 Ca value, being indistinct from the two other late forming gorilla teeth (second and third molars) available (Supplementary Data 1).…”