Shallow‐water habitats as sources of fallback foods for hominins

Abstract

Underground storage organs (USOs) have been proposed as critical fallback foods for early hominins in savanna, but there has been little discussion as to which habitats would have been important sources of USOs. USOs consumed by hominins could have included both underwater and underground storage organs, i.e., from both aquatic and terrestrial habitats. Shallow aquatic habitats tend to offer high plant growth rates, high USO densities, and relatively continuous USO availability throughout the year. Baboons in the Okavango delta use aquatic USOs as a fallback food, and aquatic or semiaquatic USOs support high‐density human populations in various parts of the world. As expected given fossilization requisites, the African early‐ to mid‐Pleistocene shows an association of Homo and Paranthropus fossils with shallow‐water and flooded habitats where high densities of plant‐bearing USOs are likely to have occurred. Given that early hominins in the tropics lived in relatively dry habitats, while others occupied temperate latitudes, ripe, fleshy fruits of the type preferred by African apes would not normally have been available year round. We therefore suggest that water‐associated USOs were likely to have been key fallback foods, and that dry‐season access to aquatic habitats would have been an important predictor of hominin home range quality. This study differs from traditional savanna chimpanzee models of hominin origins by proposing that access to aquatic habitats was a necessary condition for adaptation to savanna habitats. It also raises the possibility that harvesting efficiency in shallow water promoted adaptations for habitual bipedality in early hominins. Am J Phys Anthropol 140:630–642, 2009. © 2009 Wiley‐Liss, Inc.

Isotopic evidence for an early shift to C4resources by Pliocene hominins in Chad

“…Several studies have suggested that exploitation of energy-rich geophytes or underground storage organs (USOs) (bulbs, corms, tubers, and rhizomes) represented an important adaptive shift in hominin evolution, especially as related to the transition to early Homo (e.g., [39][40][41]. In general, most USOs are C 3 .…”

“…The remaining (C 3 ) portion of A. bahrelghazali's diet may have included C 3 macrophytes, as suggested in ref. 41, or the more "traditional" hominoid foods such as fruits, pods, flowers, and insects. The semiarid terrestrial flora that today stretches away from the current Lake Chad and colonizes the dunes includes Hyphaene thebaica (doum palm), Acacia nilotica, and Ficus ingens (42), all of which produce widely consumed fruits and pods (e.g., refs.…”

Dietary options and behavior suggested by plant biomarker evidence in an early human habitat

“…These similarities in physical attributes suggest behavioral differences were what allowed for overlapping ranges and local coexistence (sympatry) of both hominins. For instance, differences in seasonal subsistence strategies or different behavior during periods of drought and limited food could have reduced local hominin competition and fostered diversification via niche specialization (27)(28)(29). Physical and isotopic properties of fossil teeth indicate P. boisei was more water-dependent [low enamel δ…”

“…Although 13 C-enriched enamel is commonly attributed to consumption of C 4 grasses or meat from grazers (14), this was not likely, because P. boisei craniodental features are inconsistent with contemporary gramnivores (24,25) or extensive uncooked flesh mastication (26). Numerous scholars have proposed the nutritious underground storage organs (USOs) of C 4 sedges were a staple of hominin diets (14,24,26,27). Consistent with this suggestion, occurrences of n R 23 attest to the presence of sedges at FLK NN and FLK N (Fig.…”

“…Alternative foodstuffs with abrasive, 13 C-enriched biomass include seedless vascular plants (cryptogams), such as ferns and lycophytes [e.g., quillworts (27,30)]. Ferns are widely distributed throughout eastern Africa in moist and shaded microhabitats (31) and are often found near dependable sources of drinking water (32).…”