Late Pliocene environmental change during the transition from Australopithecus to Homo

We Are What, When, And How We Eat: The Evolutionary Impact of Dietary Shifts on Physical and Cognitive Development, Health, and Disease

"We are what, when, and how we eat": the evolution of human dietary habits mirrors the evolution of humans themselves. Key developments in human history, such as the advent of stone tool technology, the shift to a meat-based diet, control of fire, advancements in cooking and fermentation techniques, and the domestication of plants and animals, have significantly influenced human anatomical, physiological, social, cognitive, and behavioral changes. Advancements in scientific methods, such as the analysis of microfossils like starch granules, plant-derived phytoliths, and coprolites, have yielded unprecedented insights into past diets. Nonetheless, the isolation of ancient food matrices remains analytically challenging. Future technological breakthroughs and a more comprehensive integration of paleogenomics, paleoproteomics, paleoglycomics, and paleometabolomics will enable a more nuanced understanding of early human ancestors' diets, which holds the potential to guide contemporary dietary recommendations and tackle modern health challenges, with far-reaching implications for human well-being, and ecological impact on the planet.

A 4.3-million-year-old Australopithecus anamensis mandible from Ileret, East Turkana, Kenya, and its paleoenvironmental context

A hominin mandible, KNM-ER 63000, and associated vertebrate remains were recovered in 2011 from Area 40 in East Turkana, Kenya. Tephrostratigraphic and magnetostratigraphic analyses indicate that these fossils date to ∼4.3 Ma. KNM-ER 63000 consists of articulating but worn and weathered mandibular corpora, with a broken right M2 crown and alveoli preserved at other tooth positions. Despite extensive damage, KNM-ER 63000 preserves diagnostic anatomy permitting attribution to Australopithecus anamensis. It can be distinguished from Australopithecus afarensis by its strongly inclined symphyseal axis with a basally convex, 'cut-away' external surface, a lateral corpus that sweeps inferomedially beneath the canine-premolar row, and alignment of the canine alveolus with the postcanine axis. KNM-ER 63000 is distinguished from Ardipithecus ramidus by its thick mandibular corpus and large M2 crown. The functional trait structure and enamel's stable carbon isotopic composition of the Area 40 large-mammal community suggests an environment comparable to Kanapoi and other ∼4.5-4 Ma eastern African sites that would have offered Au. anamensis access to both C3 and C4 food resources. With an age of ∼4.3 Ma, KNM-ER 63000 is the oldest known specimen of Au. anamensis, predating the Kanapoi and Asa Issie samples by at least ∼100 kyr. This specimen extends the known temporal range of Au. anamensis and places it in temporal overlap with fossils of Ar. ramidus from Gona, Ethiopia. The morphology of KNM-ER 63000 indicates that the reconfigured masticatory system differentiating basal hominins from the earliest australopiths existed in the narrow temporal window, if any, separating the two. The very close temporal juxtaposition of these significant morphological and adaptive differences implies that Ar. ramidus was a relative rather than a direct phyletic ancestor of earliest Australopithecus.

Spatial sampling bias influences our understanding of early hominin evolution in eastern Africa

The eastern branch of the Eastern African Rift System (EARS) is the source of a large proportion of the early hominin fossil record, but it covers a tiny fraction (ca. 1%) of the continent. Here we investigate how this mismatch between where fossils are preserved and where hominins probably lived may influence our ability to understand early hominin evolution, using extant mammals as analogues. We show that the eastern branch of the EARS is not an environmentally representative sample of the full species range for nearly all extant rift-dwelling mammals. Likewise, when we investigate published morphometric datasets for extant cercopithecine primates, evidence from the eastern branch alone fails to capture major portions of continental-scale cercopithecine cranial morphospace. We suggest that extant rift-dwelling species should be used as analogues to place confidence intervals on hominin habitat reconstructions. Furthermore, given the north-south orientation of the eastern branch of the EARS, morphoclines that are not aligned along this major north-south axis are likely to be poorly sampled by sites in the eastern branch. There is a pressing need for research on the geography of early hominin morphoclines to estimate how morphologically representative the hominin fossil sample from the eastern branch may be.

Hominin turnover at Laetoli is associated with vegetation change: Multiproxy evidence from the large herbivore community

Vegetation change in eastern Africa during the Pliocene would have had an important impact on hominin adaptation and ecology, and it may have been a key driver of hominin macroevolution, including the extinction of Australopithecus and the emergence of Paranthropus and Homo. The Pliocene paleoanthropological site of Laetoli in Tanzania provides an opportunity to investigate the relationship between vegetation change and hominin turnover because it encompasses the time period when grass cover was spreading across eastern Africa and because hominin species turnover occurred locally at Laetoli, with Paranthropus aethiopicus in the Upper Ndolanya Beds (UNB) replacing Australopithecus afarensis in the Upper Laetolil Beds (ULB). However, it remains unresolved how the vegetation of the UNB and the ULB differed from each other. To examine differences between the two stratigraphic units, multiple proxies-hypsodonty, mesowear, and stable carbon isotopes of tooth enamel (δ13Cenamel)-are used to infer the diets of large herbivores and compare the dietary guild structure of the large herbivore communities. All three proxies indicate an increase in the abrasiveness and C4-content in the diets of the large herbivores in the UNB relative to those in the ULB. After inferring the diets of species based on all three proxies, the large herbivore community of the UNB had a greater proportion of grazers and a smaller proportion of mixed feeders than in the ULB but maintained a similar proportion of browsers and frugivores. The ULB community has few modern-day analogs, whereas the UNB community is most closely analogous to those in modern African grasslands. Thus, hominin turnover at Laetoli is associated with an increase in grass cover within a woodland-grassland mosaic and is part of a broader transformation of the herbivore community structure.

New Oldowan locality Sare-Abururu (ca. 1.7 Ma) provides evidence of diverse hominin behaviors on the Homa Peninsula, Kenya

The Homa Peninsula, in southwestern Kenya, continues to yield insights into Oldowan hominin landscape behaviors. The Late Pliocene locality of Nyayanga (∼3-2.6 Ma) preserves some of the oldest Oldowan tools. At the Early Pleistocene locality of Kanjera South (∼2 Ma) toolmakers procured a diversity of raw materials from over 10 km away and strategically reduced them in a grassland-dominated ecosystem. Here, we report findings from Sare-Abururu, a younger (∼1.7 Ma) Oldowan locality approximately 12 km southeast of Kanjera South and 18 km east of Nyayanga. Sare-Abururu has yielded 1754 artifacts in relatively undisturbed low-energy silts and sands. Stable isotopic analysis of pedogenic carbonates suggests that hominin activities were carried out in a grassland-dominated setting with similar vegetation structure as documented at Kanjera South. The composition of a nearby paleo-conglomerate indicates that high-quality stone raw materials were locally abundant. Toolmakers at Sare-Abururu produced angular fragments from quartz pebbles, representing a considerable contrast to the strategies used to reduce high quality raw materials at Kanjera South. Although lithic reduction at Sare-Abururu was technologically simple, toolmakers proficiently produced cutting edges, made few mistakes and exhibited a mastery of platform management, demonstrating that expedient technical strategies do not necessarily indicate a lack of skill or suitable raw materials. Lithic procurement and reduction patterns on the Homa Peninsula appear to reflect variation in local resource contexts rather than large-scale evolutionary changes in mobility, energy budget, or toolmaker cognition.

Making meaning from fragmentary fossils: Early Homo in the Early to early Middle Pleistocene

In celebration of the 50th anniversary of the Journal of Human Evolution, we re-evaluate the fossil record for early Homo (principally Homo erectus, Homo habilis, and Homo rudolfensis) from early diversification and dispersal in the Early Pleistocene to the ultimate demise of H. erectus in the early Middle Pleistocene. The mid-1990s marked an important historical turning point in our understanding of early Homo with the redating of key H. erectus localities, the discovery of small H. erectus in Asia, and the recovery of an even earlier presence of early Homo in Africa. As such, we compare our understanding of early Homo before and after this time and discuss how the order of fossil discovery and a focus on anchor specimens has shaped, and in many ways biased, our interpretations of early Homo species and the fossils allocated to them. Fragmentary specimens may counter conventional wisdom but are often overlooked in broad narratives. We recognize at least three different cranial and two or three pelvic morphotypes of early Homo. Just one postcranial morph aligns with any certainty to a cranial species, highlighting the importance of explicitly identifying how we link specimens together and to species; we offer two ways of visualizing these connections. Chronologically and morphologically H. erectus is a member of early Homo, not a temporally more recent species necessarily evolved from either H. habilis or H. rudolfensis. Nonetheless, an ancestral-descendant notion of their evolution influences expectations around the anatomy of missing elements, especially the foot. Weak support for long-held notions of postcranial modernity in H. erectus raises the possibility of alternative drivers of dispersal. New observations suggest that the dearth of faces in later H. erectus may mask taxonomic diversity in Asia and suggest various later mid-Pleistocene populations could derive from either Asia or Africa. Future advances will rest on the development of nuanced ways to affiliate fossils, greater transparency of implicit assumptions, and attention to detailed life history information for comparative collections; all critical pursuits for future research given the great potential they have to enrich our evolutionary reconstructions for the next fifty years and beyond.

Multiproxy approach to reconstruct fossil primate feeding behavior: Case study for macaque from the Plio-Pleistocene site Guefaït-4.2 (eastern Morocco)

The genus Macaca belongs to Cercopithecidae (Old World monkeys), Cercopithecinae, Papionini. The presence of Macaca in North Africa is well known from the Late Miocene to the Late Pleistocene. However, the diet of fossil Macaca has been poorly described in the literature. In this study, we investigated the feeding habits of Macaca cf. sylvanus (n = 4) from the Plio-Pleistocene site Guefaït-4.2 in eastern Morocco through multiproxy analysis combining analyses of stable carbon and oxygen isotopes from tooth enamel, buccal microtexture, and low-magnification occlusal dental microwear. For both microwear analyses, we compared the macaques with a new reference collection of extant members of Cercopithecoidea. Our occlusal microwear results show for the fossil macaque a pattern similar to the extant Cercocebus atys and Lophocebus albigena, African forest-dwelling species that are characterized by a durophagous diet based mainly on hard fruit and seed intake. Buccal microtexture results also suggest the consumption of some grasses and the exploitation of more open habitats, similar to that observed in Theropithecus gelada. The δ13C of M. cf. sylvanus indicates a C3 based-diet without the presence of C4 plants typical of the savanna grassland in eastern Africa during this period. The high δ18O values of M. cf. sylvanus, compared with the contemporary ungulates recovered from Guefaït-4.2, could be associated with the consumption of a different resource by the primate such as leaves or fresh fruits from the upper part of trees. The complementarity of these methods allows for a dietary reconstruction covering a large part of the individual’s life.

Early Pleistocene large mammals from Maka'amitalu, Hadar, lower Awash Valley, Ethiopia

The Early Pleistocene was a critical time period in the evolution of eastern African mammal faunas, but fossil assemblages sampling this interval are poorly known from Ethiopia's Afar Depression. Field work by the Hadar Research Project in the Busidima Formation exposures (~2.7-0.8 Ma) of Hadar in the lower Awash Valley, resulted in the recovery of an early Homo maxilla (A.L. 666-1) with associated stone tools and fauna from the Maka'amitalu basin in the 1990s. These assemblages are dated to ~2.35 Ma by the Bouroukie Tuff 3 (BKT-3). Continued work by the Hadar Research Project over the last two decades has greatly expanded the faunal collection. Here, we provide a comprehensive account of the Maka'amitalu large mammals (Artiodactyla, Carnivora, Perissodactyla, Primates, and Proboscidea) and discuss their paleoecological and biochronological significance. The size of the Maka'amitalu assemblage is small compared to those from the Hadar Formation (3.45-2.95 Ma) and Ledi-Geraru (2.8-2.6 Ma) but includes at least 20 taxa. Bovids, suids, and Theropithecus are common in terms of both species richness and abundance, whereas carnivorans, equids, and megaherbivores are rare. While the taxonomic composition of the Maka'amitalu fauna indicates significant species turnover from the Hadar Formation and Ledi-Geraru deposits, turnover seems to have occurred at a constant rate through time as taxonomic dissimilarity between adjacent fossil assemblages is strongly predicted by their age difference. A similar pattern characterizes functional ecological turnover, with only subtle changes in dietary proportions, body size proportions, and bovid abundances across the composite lower Awash sequence. Biochronological comparisons with other sites in eastern Africa suggest that the taxa recovered from the Maka'amitalu are broadly consistent with the reported age of the BKT-3 tuff. Considering the age of BKT-3 and biochronology, a range of 2.4-1.9 Ma is most likely for the faunal assemblage.

Mosaic habitats at Woranso-Mille (Ethiopia) during the Pliocene and implications for Australopithecus paleoecology and taxonomic diversity

Many important Pliocene hominin specimens have been recovered from Woranso-Mille, a paleontological research area in the Afar region of Ethiopia, including the complete cranium of Australopithecus anamensis, a partial skeleton of Australopithecus afarensis, mandibular and maxillary elements representing a new species, Australopithecus deyiremeda, and a partial foot of an as-yet-unnamed species. Woranso-Mille is the only site, so far, to have reported the co-existence of more than one early hominin species between 3.8 and 3.3 Ma and the temporal overlap between A. anamensis and A. afarensis. Thus, the site has important implications for our understanding of the paleoecology and taxonomic diversity of early hominins and their ecological niche. This paper explores the paleohabitats of Woranso-Mille through its faunal community ecological structure and taxonomic composition using correspondence analysis and Forbes modified similarity index. The results suggest that Pliocene Woranso-Mille was a mosaic of different habitat types, with riparian woodland and floodplain grassland along rivers draining into a lake, along with less mesic habitats such as woodland, grassland, and shrubland. The apparent high level of vegetation heterogeneity may have promoted dietary specializations and niche differentiation among the different Australopithecus species at Woranso-Mille and allowed for their co-existence at the site.

Intrataxonomic trends in herbivore enamel δ13C are decoupled from ecosystem woody cover

Analysis of enamel stable carbon isotopes (δ¹³C_enamel) of fossil herbivores is an important tool for making inferences about Plio-Pleistocene vegetation structure in Africa and the environmental context of hominin evolution. Many palaeoecological studies implicitly or explicitly assume that individual variation in C₃-C₄ plant consumption among fossil herbivores directly reflects the abundance of C₃ (trees, shrubs) or C₄ (low-altitude tropical grasses) vegetation. However, a strong link between δ¹³C_enamel of herbivores and ecosystem vegetation structure has not been rigorously established. Here we combine δ¹³C_enamel data from a large dataset (n = 1,643) with multidecadal Landsat estimates of C₃ woody cover across 30 African ecosystems to show that there is little relationship between intrataxonomic variation in δ¹³C_enamel and vegetation structure. This is especially true when removing forested ecosystems (>80% woody cover)-which numerous lines of evidence suggest are rare in the Plio-Pleistocene fossil record of eastern Africa-from our analyses. Our findings stand in contrast with the common assumption that variation in herbivore δ¹³C_enamel values reflects changes in the relative abundance of C₃-C₄ vegetation. We conclude that analyses using herbivore δ¹³C_enamel data to shed light on the environmental context of hominin evolution should look to explicitly community-level approaches for making vegetation inferences.

Dietary trends in herbivores from the Shungura Formation, southwestern Ethiopia

Diet provides critical information about the ecology and environment of herbivores. Hence, understanding the dietary strategies of fossil herbivores and the associated temporal changes is one aspect of inferring paleoenvironmental conditions. Here, we present carbon isotope data from more than 1,050 fossil teeth that record the dietary patterns of nine herbivore families in the late Pliocene and early Pleistocene (3.6 to 1.05 Ma) from the Shungura Formation, a hominin-bearing site in southwestern Ethiopia. An increasing trend toward C₄ herbivory has been observed with attendant reductions in the proportions of browsers and mixed feeders through time. A high proportion of mixed feeders has been observed prior to 2.9 Ma followed by a decrease in the proportion of mixed feeders and an increase in grazers between 2.7 and 1.9 Ma, and a further increase in the proportion of grazers after 1.9 Ma. The collective herbivore fauna shows two major change points in carbon isotope values at ∼2.7 and ∼2.0 Ma. While hominin fossils from the sequence older than 2.7 Ma are attributed to Australopithecus, the shift at ∼2.7 Ma indicating the expansion of C₄ grasses on the landscape was concurrent with the first appearance of Paranthropus The link between the increased C₄ herbivory and more open landscapes suggests that Australopithecus lived in more wooded landscapes compared to later hominins such as Paranthropus and Homo, and has implications for key morphological and behavioral adaptations in our lineage.

Earliest known Oldowan artifacts at >2.58 Ma from Ledi-Geraru, Ethiopia, highlight early technological diversity

The manufacture of flaked stone artifacts represents a major milestone in the technology of the human lineage. Although the earliest production of primitive stone tools, predating the genus Homo and emphasizing percussive activities, has been reported at 3.3 million years ago (Ma) from Lomekwi, Kenya, the systematic production of sharp-edged stone tools is unknown before the 2.58-2.55 Ma Oldowan assemblages from Gona, Ethiopia. The organized production of Oldowan stone artifacts is part of a suite of characteristics that is often associated with the adaptive grade shift linked to the genus Homo Recent discoveries from Ledi-Geraru (LG), Ethiopia, place the first occurrence of Homo ∼250 thousand years earlier than the Oldowan at Gona. Here, we describe a substantial assemblage of systematically flaked stone tools excavated in situ from a stratigraphically constrained context [Bokol Dora 1, (BD 1) hereafter] at LG bracketed between 2.61 and 2.58 Ma. Although perhaps more primitive in some respects, quantitative analysis suggests the BD 1 assemblage fits more closely with the variability previously described for the Oldowan than with the earlier Lomekwian or with stone tools produced by modern nonhuman primates. These differences suggest that hominin technology is distinctly different from generalized tool use that may be a shared feature of much of the primate lineage. The BD 1 assemblage, near the origin of our genus, provides a link between behavioral adaptations-in the form of flaked stone artifacts-and the biological evolution of our ancestors.

Dental microwear texture analysis of Pliocene Suidae from Hadar and Kanapoi in the context of early hominin dietary breadth expansion

Stable carbon isotope studies suggest that early hominins may have diversified their diet as early as 3.76 Ma. Early Pliocene hominins, including Australopithecus anamensis, had diets that were dominated by C₃ resources while Late Pliocene hominins, including Australopithecus afarensis-a putative descendant of A. anamensis-had diets that included both C₃ and C₄ resources. It has been hypothesized that the expansion of C₄ grasslands in eastern Africa during the Pliocene could have prompted hominins to incorporate C₄ resources in their diets. However, dental microwear analyses suggest that diet diversification did not involve changes in the mechanical properties of the foods consumed. To provide contextual and comparative information on this issue, the diet of suids from the A. anamensis site of Kanapoi and the A. afarensis site of Hadar is investigated. Using dental microwear texture analyses, it is shown that despite significant dietary overlap, there is evidence for dietary niche partitioning among suids. Based on comparisons with the diet of extant African suids, it is inferred that Nyanzachoerus pattersoni (n = 21) was a mixed feeder, Nyanzachoerus jaegeri (n = 4) and Notochoerus euilus (n = 61) were habitual grazers, and Kolpochoerus afarensis (n = 34) had a broad diet that included hard brittle foods and underground resources. The dental microwear of Ny. pattersoni and Ny. jaegeri/No. euilus do not differ significantly between Kanapoi and Hadar. Most differences are driven by K. afarensis, a suid absent at Kanapoi but present at Hadar. Food availability probably differed between Hadar and Kanapoi, and it is likely that A. afarensis did not exploit some of the foods (e.g., underground resources) consumed by suids. It is hypothesized that despite the incorporation of C₄ resources in the diet, a significant dietary change towards flexible diets in the hominin lineage had yet to come.

A two-million-year-long hydroclimatic context for hominin evolution in southeastern Africa

The past two million years of eastern African climate variability is currently poorly constrained, despite interest in understanding its assumed role in early human evolution^1-4. Rare palaeoclimate records from northeastern Africa suggest progressively drier conditions^2,5 or a stable hydroclimate⁶. By contrast, records from Lake Malawi in tropical southeastern Africa reveal a trend of a progressively wetter climate over the past 1.3 million years^7,8. The climatic forcings that controlled these past hydrological changes are also a matter of debate. Some studies suggest a dominant local insolation forcing on hydrological changes^9-11, whereas others infer a potential influence of sea surface temperature changes in the Indian Ocean^8,12,13. Here we show that the hydroclimate in southeastern Africa (20-25° S) is controlled by interplay between low-latitude insolation forcing (precession and eccentricity) and changes in ice volume at high latitudes. Our results are based on a multiple-proxy reconstruction of hydrological changes in the Limpopo River catchment, combined with a reconstruction of sea surface temperature in the southwestern Indian Ocean for the past 2.14 million years. We find a long-term aridification in the Limpopo catchment between around 1 and 0.6 million years ago, opposite to the hydroclimatic evolution suggested by records from Lake Malawi. Our results, together with evidence of wetting at Lake Malawi, imply that the rainbelt contracted toward the Equator in response to increased ice volume at high latitudes. By reducing the extent of woodland or wetlands in terrestrial ecosystems, the observed changes in the hydroclimate of southeastern Africa-both in terms of its long-term state and marked precessional variability-could have had a role in the evolution of early hominins, particularly in the extinction of Paranthropus robustus.