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1. Functional and developmental influences on intraspecific variation in catarrhine vertebrae

   https://doi.org/10.1002/ajpa.23730  

   Shapiro, Liza J. ; Kemp, Addison D. ( November 2018 , American Journal of Physical Anthropology)

   We tested whether patterns of intraspecific variation in catarrhine vertebral shape are consistent with developmental or functional predictions. Intraspecific variation was compared across column regions, morphological features, and species. Transitional regions and later ossifying morphological features were predicted to exhibit increased variation. The lumbosacral region, biomechanically important morphological features, and species with high locomotor demand and/or dedicated pronogrady were predicted to exhibit decreased variation.

   We used a modified Levene's test to compare intraspecific variation in dimensions of the neural canal, vertebral bodies, and spinous and transverse processes in lower thoracic to proximal sacral vertebrae. The sample included all hominoid genera and one cercopithecoid (Chlorocebus).

   We found little difference in variation across regions of the vertebral column. In hominoids, vertebral body dimensions were the least variable, neural canal dimensions the most variable, with spinous and transverse processes generally intermediate. Among species, there was a general though not always significant pattern forChlorocebusto exhibit the least variation, followed byHomoorHylobates.

   Patterns of variation across morphological features may reflect the complex interaction of functional constraints, developmental timing, and/or variable biomechanical forces.Pongo's elevated variation in spinous process length suggests a release from functional constraint, consistent with its suspensory locomotion and reduced spinous processes. Interspecific differences in vertebral variation based on locomotor demand or posture are generally consistent with patterns previously reported for vertebral formula and other aspects of morphology. Future research would benefit from an expanded taxonomic sample and more detailed analyses of vertebral modularity and developmental timing.

    

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2. The evolution of hominoid locomotor versatility: Evidence from Moroto, a 21 Ma site in Uganda

   https://doi.org/10.1126/science.abq2835  

   MacLatchy, Laura M. ; Cote, Susanne M. ; Deino, Alan L. ; Kityo, Robert M. ; Mugume, Amon A. ; Rossie, James B. ; Sanders, William J. ; Cosman, Miranda N. ; Driese, Steven G. ; Fox, David L. ; et al ( April 2023 , Science)

   INTRODUCTION Inherent in traditional views of ape origins is the idea that, like living apes, early large-bodied apes lived in tropical forests. In response to constraints related to locomoting in forest canopies, it has been proposed that early apes evolved their quintessential upright torsos and acrobatic climbing and suspensory abilities, enhancing their locomotor versatility, to distribute their weight among small supports and thus reach ripe fruit in the terminal branches. This feeding and locomotor transition from a quadruped with a horizontal torso is thought to have occurred in the Middle Miocene due to an increasingly seasonal climate and feeding competition from evolving monkeys. Although ecological and behavioral comparisons among living apes and monkeys provide evidence for versions of terminal branch forest frugivory hypotheses, corroboration from the early ape fossil record has been lacking, as have detailed reconstructions of the habitats where the first apes evolved. RATIONALE The Early Miocene fossil site of Moroto II in Uganda provides a unique opportunity to test the predictions of terminal branch forest frugivory hypotheses. Moroto II documents the oldest [21 million years ago (Ma)] well-established paleontological record of ape teeth and postcranial bones from a single locality and preserves paleoecological proxies to reconstruct the environment. The following lines of evidence from Moroto II were analyzed: (i) the functional anatomy of femora and a vertebra attributed to the ape Morotopithecus ; (ii) dental traits, including molar shape and isotopic profiles of Morotopithecus enamel; (iii) isotopic dietary paleoecology of associated fossil mammals; (iv) biogeochemical signals from paleosols (ancient soils) that reflect local relative proportions of C 3 (trees and shrubs) and C 4 (tropical grasses and sedges that can endure water stress) vegetation as well as rainfall; and (v) assemblages of phytoliths, microscopic plant-derived silica bodies that reflect past plant communities. RESULTS A short, strong femur biomechanically favorable to vertical climbing and a vertebra indicating a dorsostable lower back confirm that ape fossils from Moroto II shared locomotor traits with living apes. Both Morotopithecus and a smaller ape from the site have elongated molars with well-developed crests for shearing leaves. Carbon isotopic signatures of the enamel of these apes and of other fossil mammals indicate that some mammals consistently fed on water-stressed C 3  plants, and possibly also C 4  vegetation, in a woodland setting. Carbon isotope values of pedogenic carbonates, paleosol organic matter, and plant waxes all point to substantial C 4 grass biomass on the landscape. Analysis of paleosols also indicates subhumid, strongly seasonal rainfall, and phytolith assemblages include forms from both arid-adapted C 4 grasses and forest-indicator plants. CONCLUSION The ancient co-occurrence of dental specializations for leaf eating, rather than ripe fruit consumption, along with ape-like locomotor abilities counters the predictions of the terminal branch forest frugivory hypotheses. The combined paleoecological evidence situates Morotopithecus in a woodland with a broken canopy and substantial grass understory including C 4 species. These findings call for a new paradigm for the evolutionary origins of early apes. We propose that seasonal, wooded environments may have exerted previously unrecognized selective pressures in the evolution of arboreal apes. For example, some apes may have needed to access leaves in the higher canopy in times of low fruit availability and to be adept at ascending and descending from trees that lacked a continuous canopy. Hominoid habitat comparisons. Shown are reconstructions of a traditionally conceived hominoid habitat ( A ) and the 21 Ma Moroto II, Uganda, habitat ( B ). 

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3. 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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4. 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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5. Relative tooth size, Bayesian inference, and Homo naledi

   https://doi.org/10.1002/ajpa.24353  

   Irish, Joel D. ; Grabowski, Mark ( June 2021 , American Journal of Physical Anthropology)

   Size‐corrected tooth crown measurements were used to estimate phenetic affinities amongHomo naledi(~335–236 ka) and 11 other Plio‐Pleistocene and recent species. To assess further their efficacy, and identify dental evolutionary trends, the data were then quantitatively coded for phylogenetic analyses. Results from both methods contribute additional characterization ofH. naledirelative to other hominins.

   After division by their geometric mean, scaled mesiodistal and buccolingual dimensions were used in tooth size apportionment analysis to compareH. nalediwithAustralopithecus africanus,A. afarensis,Paranthropus robustus,P. boisei,H. habilis,H. ergaster,H. erectus,H. heidelbergensis,H. neanderthalensis,H. sapiens, andPan troglodytes. These data produce equivalently scaled samples unaffected by interspecific size differences. The data were then gap‐weighted for Bayesian inference.

   Congruence in interspecific relationships is evident between methods, and with many inferred from earlier systematic studies. However, the present results placeH. naledias a sister taxon toH. habilis,based on a symplesiomorphic pattern of relative tooth size. In the preferred Bayesian phylogram,H. nalediis nested within a clade comprising allHomospecies, but it shares some characteristics with australopiths and, particularly, earlyHomo.

   Phylogenetic analyses of relative tooth size yield information about evolutionary dental trends not previously reported inH. nalediand the other hominins. Moreover, with an appropriate model these data recovered plausible evolutionary relationships. Together, the findings support recent study suggestingH. naledioriginated long before the geological date of the Dinaledi Chamber, from which the specimens under study were recovered.

    

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