More Like this

1. Reconstructing the climate and ecology of an Early Miocene tropical forest on the flanks of the Tinderet Volcano, Kisumu County, western Kenya

   MUNYAKA, Venanzio; OGINGA, Kennedy Ogonda; COTE, Susanne; HEAD, Jason; LUKENS, William; LUTZ, James A; KINYANJUI, Rahab N; MANTHI, Fredrick K; MCNULTY, Kieran P; HALL, Abigail; et al (October 2023, Geological Society of America Abstracts with Programs)

   Tectonically driven physiographic evolution has profound effects on the climate and vegetation of Early Miocene terrestrial ecosystems across eastern Africa, creating habitat heterogeneity. Early hominoids were present on these dynamic landscapes, which likely influenced their evolutionary history. In western Kenya, a series of Early Miocene (ca.19-21Ma) fossiliferous exposures around the now-extinct Tinderet volcano document this history through preservation of hominoid fossils, fossil leaves, tree stump casts, and paleosols. Here, we use multiple proxies to reconstruct the paleoclimate and paleoecology of the fossil site Koru-16. Sedimentological and stratigraphic analysis indicate the landscape was disturbed by periodic eruptions of the volcano followed by intervals of stability, as shown by features of moderate to poorly developed paleosols. Paleoclimate estimates using the paleosol-paleoclimate model (PPM) indicate warm and wet climate conditions. Over 1000 fossil leaves were collected from two stratigraphic intervals. Seventeen morphotypes were identified across both sites, with an unequal distribution of morphotypes. Average leaf size estimate is mesophyll to megaphyll, with mean annual precipitation estimates using leaf physiognomic methods indicate >2000mm/yr. Leaf lifespan reconstructions based on leaf mass per area (MA) proxy indicate the site was predominately evergreen, with few deciduous taxa, with a MA distribution like modern tropical rainforests and tropical seasonal forests in equatorial Africa. Forest density estimates based on fossil tree stump casts indicate an open forest, with density similar to modern tropical forests that support large-bodied primates. Importantly, fossil leaves, tree stump casts, a medium-sized pythonid, a large-bodied hominoid and Proconsul africanus are all found within the same strata, indicating that these early apes lived within the reconstructed Koru-16 ecosystem. Our multi-proxy paleoclimate and paleoecological reconstructions indicate Koru-16 site sampled a very wet and warm climate that supported a tropical seasonal forest to rainforest biome. This likely provided an ideal habitat for hominoids and suggests that forested habitats played a role in the evolution of Early Miocene hominoids. 

   more » « less
2. 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
3. Paleoclimate reconstructions of the Early Miocene hominoid fossil sites from Chamtwara, Legetet and Koru, Tinderet, western Kenya

   PEPPE, Daniel; MCNULTY, Kieran P; COTE, Susanne; HEAD, Jason; MUNYAKA, Venanzio; OGINGA, Kennedy Ogonda; KINYANJUI, Rahab N; LUKENS, William E; LUTZ, James A; TEGART, Amanda (October 2023, Geological Society of America Abstracts with Programs)

   Hominoids exhibited high diversity in the early Neogene. The Early Miocene, in particular, is the inferred timing of the origin of the crown Hominoidea. Thus, understanding the paleoecology and paleoenvironments of the Early Miocene is critical for understanding the selective pressures that led to the evolution and diversification of hominoids. The Early Miocene fossil sites of Koru, Legetet, and Chamtwara occur on the southwestern flank of the now-extinct Tinderet volcano in western Kenya. While not as well- known as the Songhor site on the northwestern flank of the same volcano, the Chamtwara, Legetet, and Koru sites surrounding the village of Koru document surprising taxonomic diversity of Early Miocene hominoids; yet relatively little paleoenvironmental work has been conducted to contextualize this taxonomic diversity. Our recent geological, paleontological, and paleoenvironmental work has focused on reconstructing the paleoclimate and paleoecology of these fossil sites using a variety of proxies. Sedimentological analyses of the fossil sites indicate periodic disturbance of the landscape due to volcanic activity and that most of the fossiliferous strata are moderately to poorly developed paleosols and fluvial channels. Paleosol features are nearly identical across sites and demonstrate relatively wet and well-drained conditions with some evidence of seasonality and/or periodic water deficit. Paleosol based proxies for paleoclimate indicate wet conditions with mean annual precipitation greater than 175 cm/year. Paleobotanical proxies from fossil leaves and fossil tree stump casts indicate a warm and very wet climate indicating a tropical seasonal forest to tropical rainforest biome. Paleoclimate estimates based on habitats of extant relatives and vertebral ecomorphology of fossil snakes similarly indicate very warm and wet conditions consistent with tropical rainforests. Faunal analyses of the mammal community composition and dietary ecology also indicate forested environments. Taken together, our multi-proxy reconstructions of paleoclimate and paleoenvironment indicate that the Chamtwara, Legetet, and Koru sites were warm and very wet forested habitats connecting early hominoids to closed habitats. 

   more » « less
4. 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
5. New surveys at the Tinderet fossil complex, Nyanza Rift, Kenya

   McNulty, Kieran P; Cote, Susanne; Hall, Abigail S; Head, Jason J; Kinyanjui, Rahab N; Manthi, Fredrick Kyalo; Munyaka, Venanzio; Peppe, Daniel J (July 2024, Eastern African Association of Palaeoanthropology and Palaeontology)

   The first fossil apes published from Africa were discovered in the 1920s at the Tinderet site of Koru, Kenya. Since that time, the entire Tinderet fossil complex has produced thousands of fossil mammals, reptiles, and plants, including some of the most important early ape and stem catarrhine specimens. Here, we report results from geological, paleoecological, and paleontological surveys and samples conducted by our team between 2013-2023. A major part of our work has been to rediscover old but sometimes poorly documented fossil sites and to assess their potential for future research. One such site, Tonde Bridge, was thought to have no remaining fossil deposits but we report here the discovery of many new specimens. We have also discovered new fossil sites that may sample poorly known depositional and/or ecological settings. Our stratigraphic and geochronological results help to better ordinate major fossil outcrops with respect to each other. We have also specifically targeted the smallest microfauna as well as understudied taxonomic groups such as reptiles and amphibians. This work combined with other paleoecological analyses confirm closed habitats at many of the Tinderet sites. One site in particular has benefitted from extensive multi-proxy paleoecological reconstruction, allowing us to place some fossil apes within a dense forested environment. Finally, the discovery of important new primate specimens helps clarify some of the anatomical variation represented in historic collections but also extends the taxonomic variation from Tinderet. In particular, the discovery of a large-bodied nyanzapithecine from Koru suggests that size variation in this clade may have been similar to that found in proconsulids. 

   more » « less