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1. Monkeys in the Middle: Modeling ecological flexibility and niche construction in African cercopithecid primates

   Smail, Irene E. ( March 2020 , Program of the Annual Meeting of the American Association of Physical Anthropologists)

   Niche construction is broadly defined as an organism’s influence over its environment, ranging from the depletion of local resources to the intentional modification of landscapes and ecosystems. While modern humans excel at the latter, the exact timing and nature of our transition to being complex cultural niche constructors remains to be determined. Here I use methods taken from community ecology to develop a baseline model of minimal niche construction within a group of primate generalists. This serves as an important comparison for interpretations of the hominin fossil record and broader paleontological record to determine when and how our hominin ancestors began to diverge from this pattern. Dental metric data were used in principal components analysis to reconstruct the dietary ecomorphological niches of a sample African cercopithecid primates from the Plio-Pleistocene to today. Potential niche construction is identified through the displacement of co-occurring species indicating that the focal taxon has excluded potential competitors through resource depletion. Overall, fossil taxa are shown to occupy a more restricted niche than their extant relatives, but otherwise exhibit similar patterns of dispersion and overlap within and across communities. The lack of consistent trends within the Plio-Pleistocene sample — either through time or in response to potential confamilial competition — supports the idea that these generalized primates are not exerting a significant influence over their local environments. I conclude with some suggestions on expanding these analyses to look for evidence of niche construction in other paleontological and paleoanthropological contexts. 

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2. Fine-scaled climate variation in equatorial Africa revealed by modern and fossil primate teeth

   https://doi.org/10.1073/pnas.2123366119  

   Green, Daniel R. ; Ávila, Janaina N. ; Cote, Susanne ; Dirks, Wendy ; Lee, Daeun ; Poulsen, Christopher J. ; Williams, Ian S. ; Smith, Tanya M. ( August 2022 , Proceedings of the National Academy of Sciences)

   Variability in resource availability is hypothesized to be a significant driver of primate adaptation and evolution, but most paleoclimate proxies cannot recover environmental seasonality on the scale of an individual lifespan. Oxygen isotope compositions (δ 18 O values) sampled at high spatial resolution in the dentitions of modern African primates ( n = 2,352 near weekly measurements from 26 teeth) track concurrent seasonal precipitation, regional climatic patterns, discrete meteorological events, and niche partitioning. We leverage these data to contextualize the first δ 18 O values of two 17 Ma Afropithecus turkanensis individuals from Kalodirr, Kenya, from which we infer variably bimodal wet seasons, supported by rainfall reconstructions in a global Earth system model. Afropithecus ’ δ 18 O fluctuations are intermediate in magnitude between those measured at high resolution in baboons ( Papio spp.) living across a gradient of aridity and modern forest-dwelling chimpanzees ( Pan troglodytes verus ). This large-bodied Miocene ape consumed seasonally variable food and water sources enriched in 18 O compared to contemporaneous terrestrial fauna ( n = 66 fossil specimens). Reliance on fallback foods during documented dry seasons potentially contributed to novel dental features long considered adaptations to hard-object feeding. Developmentally informed microsampling recovers greater ecological complexity than conventional isotope sampling; the two Miocene apes ( n = 248 near weekly measurements) evince as great a range of seasonal δ 18 O variation as more time-averaged bulk measurements from 101 eastern African Plio-Pleistocene hominins and 42 papionins spanning 4 million y. These results reveal unprecedented environmental histories in primate teeth and suggest a framework for evaluating climate change and primate paleoecology throughout the Cenozoic. 

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3. The first hominin from the early Pleistocene paleocave of Haasgat, South Africa

   https://doi.org/10.7717/peerj.2024  

   Leece, AB ; Kegley, Anthony D.T. ; Lacruz, Rodrigo S. ; Herries, Andy I.R. ; Hemingway, Jason ; Kgasi, Lazarus ; Potze, Stephany ; Adams, Justin W. ( May 2016 , PeerJ)

   Haasgat is a primate-rich fossil locality in the northeastern part of the Fossil Hominid Sites of South Africa UNESCO World Heritage Site. Here we report the first hominin identified from Haasgat, a partial maxillary molar (HGT 500), that was recovered from anex situcalcified sediment block sampled from the locality. Thein situfossil bearing deposits of the Haasgat paleokarstic deposits are estimated to date to slightly older than 1.95 Ma based on magnetobiostratigraphy. This places the hominin specimen at a critical time period in South Africa that marks the last occurrence ofAustralopithecusaround 1.98 Ma and the first evidence ofParanthropusandHomoin the region between ∼2.0 and 1.8 Ma. A comprehensive morphological evaluation of the Haasgat hominin molar was conducted against the current South African catalogue of hominin dental remains and imaging analyses using micro-CT, electron and confocal microscopy. The preserved occlusal morphology is most similar toAustralopithecus africanusor earlyHomospecimens but different fromParanthropus. Occlusal linear enamel thickness measured from micro-CT scans provides an average of ∼2.0 mm consistent withAustralopithecusand earlyHomo. Analysis of the enamel microstructure suggests an estimated periodicity of 7–9 days. Hunter–Schreger bands appear long and straight as in someParanthropus, but contrast with this genus in the short shape of the striae of Retzius. Taken together, these data suggests that the maxillary fragment recovered from Haasgat best fits within theAustralopithecus—earlyHomohypodigms to the exclusion of the genusParanthropus. At ∼1.95 Ma this specimen would either represent another example of late occurringAustralopithecusor one of the earliest examples ofHomoin the region. While the identification of this first hominin specimen from Haasgat is not unexpected given the composition of other South African penecontemporaneous site deposits, it represents one of the few hominin localities in the topographically-distinct northern World Heritage Site. When coupled with the substantial differences in the mammalian faunal communities between the northern localities (e.g., Haasgat, Gondolin) and well-sampled Bloubank Valley sites (e.g., Sterkfontein, Swartkrans, Kromdraai), the recovery of the HGT 500 specimen highlights the potential for further research at the Haasgat locality for understanding the distribution and interactions of hominin populations across the landscape, ecosystems and fossil mammalian communities of early Pleistocene South Africa. Such contextual data from sites like Haasgat is critical for understanding the transition in hominin representation at ∼2 Ma sites in the region fromAustralopithecustoParanthropusand earlyHomo.

    

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4. A Pleistocene assemblage of near‐modern Papio hamadryas from the Middle Awash study area, Afar Rift, Ethiopia

   https://doi.org/10.1002/ajpa.24634  

   Brasil, Marianne F. ; Monson, Tesla A. ; Taylor, Catherine E. ; Yohler, Ryan M. ; Hlusko, Leslea J. ( November 2022 , American Journal of Biological Anthropology)

   The aim of this study is to assess a new assemblage of papionin fossils (n = 143) recovered from later Pleistocene sediments in the Middle Awash study area in the Afar Rift of Ethiopia.

   We collected metric and qualitative data to compare the craniodental and postcranial anatomy of the papionin fossils with subspecies of modernPapio hamadryasand with Plio‐Pleistocene African papionins. We also estimated sex and ontogenetic age.

   The new fossils fit well within the range of morphological variation observed for extantP. hamadryas, overlapping most closely in dental size and proportions with theP. h. cynocephalusindividuals in our extant samples, and well within the ranges ofP. h. anubisandP. h. hamadryas. The considerable overlap in craniodental anatomy with multiple subspecies precludes subspecific diagnosis. We therefore referred 143 individuals toP. hamadryasssp. The majority of the individuals assessed for ontogenetic age fell into middle‐ and old‐adult age categories based on the degree of dental wear. Males (26%) were better represented than females (12%) among individuals preserving the canine‐premolar honing complex.

   These new near‐modernP. hamadryasfossils provide a window into population‐level variation in the later Pleistocene. Our findings echo previous suggestions from genomic studies that the papionin family tree may have included a ghost population and provide a basis for future testing of hypotheses regarding hybridization in the recent evolutionary history of this taxon.

    

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5. ISOTOPIC EVIDENCE OF SEASONALITY AND MIGRATION DURING THE LAST GLACIAL PERIOD OF KENYA

   O'Brien, K. ; Podkovyroff, K. ; Fernandez, D. P. ; Tryon, C. A. ; Cerling, T. E. ; Ashioya, L. ; Faith, J. T. ( October 2023 , Society of Vertebrate Paleontology)

   Paleoenvironmental reconstructions of the Last Glacial Period of eastern Africa paint a picture of a landscape dominated by grasslands and herds of diverse grazing herbivores unlike anywhere in modern Africa. However, the scale of such reconstructions is often at the site level and greatly time-averaged. To elucidate the impact of glacial conditions on tropical grassland animal behavior, a more direct proxy is needed. Using stable strontium, carbon, and oxygen isotopes, we reconstruct paleoenvironmental conditions and behavior of 18 bovid and equid species from four sites dating to the Last Glacial Period in Kenya (Karungu, Rusinga, Kibogo, and Lukenya Hill). In doing so, we address i) migration patterns, ii) seasonality of precipitation and diet, and iii) the role that seasonal responses played in niche separation of closely related species. We find that migration played a similar role in Last Glacial Period grasslands to what it does today but with a notably different set of species; that animals had relatively stable, grass-dominated diets year-round, peaking in C4 grass abundance during the Last Glacial Maximum; that precipitation and seasonality fell within the range of modern eastern African ecosystems; and that a diverse guild of ungulate grazers was able to coexist due to niche separation detectable as isotopic differences. These results combine to extend the theory that eastern African grasslands were greatly expanded and resource-rich year-round during the Last Glacial Period, creating highly favorable conditions for grazing ungulates. Additionally, they demonstrate the geologic recency of the modern guild of migratory species in eastern Africa, which replaced a set of now-extinct migratory species once common in grasslands during the Last Glacial Period, most notably the enigmatic bovid Rusingoryx. Our results illustrate the ecosystem dynamics of Late Pleistocene Kenya on a scale not attainable with most other paleoenvironmental proxies: the scale of individual animals’ lifetimes. This is nearly as close as possible to an actualistic ecological survey of ungulate behavior during the Last Glacial Period in a setting not analogous to any ecosystem on Earth today. 

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