More Like this

1. 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 ). 

   more » « less
2. The reconstructed cranium of Pierolapithecus and the evolution of the great ape face

   https://doi.org/10.1073/pnas.2218778120  

   Pugh, Kelsey D; Catalano, Santiago A; Pérez_de_los_Ríos, Miriam; Fortuny, Josep; Shearer, Brian M; Vecino_Gazabón, Alessandra; Hammond, Ashley S; Moyà-Solà, Salvador; Alba, David M; Almécija, Sergio (October 2023, Proceedings of the National Academy of Sciences)

   Pierolapithecus catalaunicus(~12 million years ago, northeastern Spain) is key to understanding the mosaic nature of hominid (great ape and human) evolution. Notably, its skeleton indicates that an orthograde (upright) body plan preceded suspensory adaptations in hominid evolution. However, there is ongoing debate about this species, partly because the sole known cranium, preserving a nearly complete face, suffers from taphonomic damage. We 1) carried out a micro computerized tomography (CT) based virtual reconstruction of thePierolapithecuscranium, 2) assessed its morphological affinities using a series of two-dimensional (2D) and three-dimensional (3D) morphometric analyses, and 3) modeled the evolution of key aspects of ape face form. The reconstruction clarifies many aspects of the facial morphology ofPierolapithecus. Our results indicate that it is most similar to great apes (fossil and extant) in overall face shape and size and is morphologically distinct from other Middle Miocene apes. Crown great apes can be distinguished from other taxa in several facial metrics (e.g., low midfacial prognathism, relatively tall faces) and only some of these features are found inPierolapithecus, which is most consistent with a stem (basal) hominid position. The inferred morphology at all ancestral nodes within the hominoid (ape and human) tree is closer to great apes than to hylobatids (gibbons and siamangs), which are convergent with other smaller anthropoids. Our analyses support a hominid ancestor that was distinct from all extant and fossil hominids in overall facial shape and shared many features withPierolapithecus. This reconstructed ancestral morphotype represents a testable hypothesis that can be reevaluated as new fossils are discovered. 

   more » « less
3. RECONSTRUCTING THE CLIMATE AND ECOLOGY OF AN EARLY MIOCENE TROPICAL FOREST ON THE FLANKS OF THE TINDERET VOLCANO, NYANZA PROVINCE, WESTERN KENYA

   Munyaka, Venanzio; Oginga, Kennedy; Cote, Susanne; Head, Jason J; Lukens, William; Kinyanjui, Rahab N; Manthi, Fredrick Kyalo; McNulty, Kieran P; Hall, Abigail S; Tegart, A (July 2024, University of Michigan Papers on Paleontology)

   Eastern African terrestrial ecosystems in the Early Miocene are characterized by habitat heterogeneity resulting from local rifting, climate variation, and biogeography. These dynamic landscapes profoundly influenced the evolutionary trajectories of hominoids and other mammals. In western Kenya, a collection of Early Miocene fossil-rich sites (ca. 20 Ma) proximate to the extinct Tinderet Volcano, offers a unique window into understanding habitat preferences and ecological drivers to the evolution of hominoids. Here, we present data from one of the sites, Koru 16, with evidence of remarkably preserved fossil fauna, fossil leaves, tree stump casts, and paleosols, to provide invaluable insights into the ancient ecological dynamics of the region. We use multiple proxies to reconstruct the paleoclimate and paleoecology of the Koru 16 site. The lithofacies of the Koru 16 area are characterized as interbedded ash and weakly developed paleosols indicating episodic landscape disturbance from eruptions of the volcano followed by intervals of stability. Paleosol features together with paleoclimate estimates using two models based on elemental weathering (RF-MAP and PPM) indicate warm and wet conditions. More than 1000 fossil leaves collected from two stratigraphic locations at Koru 16 yielded seventeen morphotypes which were identified across both localities and displaying different distributions of morphotypes between them. The average leaf size of morphotypes form both localities is mesophyll to megaphyll and mean annual precipitation estimates using multiple leaf physiognomic methods indicate >2000 mm/yr. Leaf lifespan estimates derived from the leaf mass per area (MA) proxy suggest that the site was predominantly characterized by evergreen taxa, with limited deciduous taxa. The distribution of MA is consistent with tropical rainforests and tropical seasonal forests in equatorial Africa, indicating similarities in leaf characteristics and ecological patterns. Tree stump casts corroborate this observation, as they indicate an open forest, with density similar to modern tropical forests that support large-bodied primates. The fauna includes a medium- sized pythonid, and at least two species of apes, along with other mammalian taxa typical for the early Miocene. Our comprehensive paleoclimate and paleoecological analyses suggest that the Koru 16 site was very warm and wet, which is a climate conducive for a tropical seasonal forest transitioning into a rainforest biome. This environmental reconstruction underscores the broad distribution of Early Miocene apes in a variety of habitats, and calls into question a recent hypothesis that apes only lived in environments with a significant open component. 

   more » « less
4. 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. 

   more » « less
5. Plant community and climatic response to mid-Miocene environmental change in the Pacific Northwest (USA) within a refined temporal framework

   https://doi.org/10.1130/abs/2021AM-367337  

   Lowe, A.J.; Strömberg, C.A.E; Schmitz, M.; Dillhoff, T.; Dillhoff, R.; Rember, W. (October 2021, Geological Society of America Abstracts with Programs)

   The US Pacific Northwest (PNW), including Washington, Oregon, and Idaho, hosts an extensive suite of Oligocene–Miocene fossil plant sites that have the potential to showcase terrestrial vegetation and climate response to several pronounced environmental perturbations. These include the Mid-Miocene Climatic Optimum (MMCO; ca. 17-14 Ma), the Middle Miocene Climatic Transition (MMCT; ca. 14-13 Ma), and the eruption of the Columbia River Basalts (~95% of its volume 16.7 to 15.9 Ma). This collaborative study focuses on 18 PNW fossil plant sites spanning ca. 32 to 10 Ma, many of which have extensive pre-existing macrofossil collections. First, we radiometrically date interbedded tuffs at these sites to establish a high-resolution temporal framework, using U-Pb/CA-ID-TIMS. We present new dates for the Clarkia/Emerald Creek, Alvord Creek, Juliaetta, Pickett Creek, Whitebird, and Trout Creek fossil sites. Within this temporal framework, we are: 1) documenting regional climate change in the PNW during the MMCO and MMCT using paleobotany-based paleoclimate proxies, and 2) providing an integrated perspective on the response of plant communities to these mid-Miocene environmental changes by combining macrofossil, palynomorph, and phytolith evidence. Taken together, these data will provide a regionally-comprehensive perspective on the sensitivity of terrestrial vegetation and climate to global climatic events known more extensively from marine records. 

   more » « less