Paleoclimate and Paleoenvironments of Early to Middle Miocene strata in West Turkana, Kenya: proxy records of forests, woodlands, and hydroclimate change

2026-03-14

The Lothidok Range west of Lake Turkana, Kenya contains a rich paleontological record, including multiple well-preserved Miocene fossil ape taxa. Our work, as part of the West Turkana Miocene Project, seeks to integrate new paleontological surveys with modern tools in geologic mapping, stratigraphic analysis, geochronology, and proxy-based climatic and environmental reconstructions. The Early Miocene Moruorot and Kalodirr localities are well known for fossils of the ape taxa Afropithecus, Turkanapithecus, and Simiolus. Our work at Moruorot demonstrates that these ape taxa were coeval and are preserved in humid alluvial fan complexes. Paleovegetation proxies based on stable carbon isotope ratios in paleosol organic matter (δ13Com = -28 to -31 ‰) and pedogenic carbonates (δ13Cpc = -9 to -12 ‰) are consistent with C3 plants thriving in a forested ecosystem. This interpretation is bolstered by the presence of calcified branches and fruits in lahar deposits. We also use a paleosol bulk geochemical proxy for mean annual precipitation (MAP), which yields values of 1700-1900 mm, which requires intense seasonality of rainfall for pedogenic carbonate stability. In contrast to the Early Miocene paleoenvironments, nearby Middle Miocene deposits at Esha that contain at least one newly discovered fossil ape taxon preserve floodplain paleosols that suggest seasonal woodland conditions (δ13Com = -19 to - 27‰, δ13Cpc = -6.5 to -12 ‰) with a minor fraction of C4 plants in a C3-dominated biome. The paleosol bulk geochemical proxy yields MAP estimates of 500-1000 mm, notably drier than the Early Miocene paleosols. This multi-proxy investigation demonstrates that the West Turkana region experienced drying from the Early to Middle Miocene, and that both time intervals were much wetter than modern conditions. Our ongoing work is focused on refining the stratigraphy and geochronology at both known and newly discovered Early and Middle Miocene sites, and placing systematically collected fossils within a well resolved geological and paleoenvironmental framework across the southern Lothidok Range.

Allometry and Evolution of Neurocranial Narrowness Across Nonhuman Anthropoid Primates

American Journal of Biological Anthropology · 2026-02-01

OBJECTIVES: Among anthropoid primates, small-bodied platyrrhines exhibit striking mediolateral narrowness of the neurocranium relative to larger-bodied platyrrhines. Body size allometry has been hypothesized to explain variation in neurocranial narrowness. However, interspecific catarrhine variation appears inconsistent with the proposed platyrrhine allometry. This study tested the relationship between body size and neurocranial narrowness across anthropoids to identify whether clade-specific allometries have evolved. We further estimated neurocranial narrowness in anthropoid ancestors to determine the trait's evolutionary polarity. METHODS: Inter-clade shifts in degree and allometric scaling of neurocranial narrowness were identified with GLS pANCOVA, which combines generalized least-squares analysis (GLS) and phylogenetic analysis of covariance (pANCOVA). Ancestral trait estimation was performed using parsimony reconstruction methods, based on linear measurements of extant and fossil anthropoid skulls. RESULTS: In callitrichine and female cebine platyrrhines, neurocranial narrowness was significantly greater than predicted by body size and displayed a different allometric relationship than in other anthropoids. This shift is correlated with decreased neurocranial breadth in callitrichines, but not cebines. Neurocranial narrowness was not correlated with body size in most anthropoid clades. DISCUSSION: We did not identify a unified neurocranial narrowness allometry across platyrrhines or across anthropoids collectively. Nonetheless, reduced narrowness occurred parallel to the evolution of increased body size in catarrhines, atelids, and pitheciids, suggesting that larger body size may mitigate constraints on neurocranial shape responsible for narrow neurocrania in small-bodied fossil anthropoids, which have been retained only in small-bodied platyrrhines. Feeding adaptations and brain size also provide potential explanations for neurocranial narrowness variation in some clades.

Neurocranial narrowness across nonhuman anthropoid primates

Open MIND · 2026-02-02

Body size allometry has been proposed to explain neurocranial shape variation across platyrrhine monkeys, including the extreme neurocranial narrowness (NCN) of small-bodied taxa. However, catarrhine primates do not align with the proposed platyrrhine allometry, suggesting that body size alone may not explain anthropoid NCN variation. We measured NCN in platyrrhine and catarrhine anthropoids, and identified inter-clade differences in degree and allometric scaling of NCN using GLS pANCOVA, a method combining generalized least squares analysis and phylogenetic analysis of covariance. We further performed character history analysis using extant anthropoid data and fossil evidence to estimate neurocranial shape in anthropoid ancestors. We found no unified allometry of NCN across platyrrhines or across anthropoids as a whole, and there was no significant correlation between body mass and NCN across platyrrhines or catarrhines. At the subfamily level, callitrichine and possibly cebine platyrrhines differ from other anthropoids in degree and allometric scaling of NCN. Character history analysis suggests that higher NCN is the ancestral platyrrhine condition, and broader neurocranial shape evolved independently in catarrhines and larger-bodied platyrrhines. Our results support the hypothesis that body size does not explain anthropoid NCN variation, and provide a foundation for future research into potential correlates of anthropoid NCN.

New fossils reveal the hand of Paranthropus boisei

Nature · 2025-10-15 · 7 citations

When Mary Leakey discovered the OH 5 cranium of Paranthropus boisei alongside Oldowan stone artefacts, it was declared “the oldest yet discovered maker of stone tools”1. Whether Paranthropus made and used tools has been debated ever since2–4, largely because there are no known hand bones that can be definitively attributed to this genus. Here we report fossil hand and foot bones unambiguously associated with craniodental material of P. boisei. KNM-ER 101000 demonstrates that P. boisei shared key manipulative and bipedal adaptations with the genus Homo. Moreover, the hand morphology of KNM-ER 101000 converges on that of gorillas in ways that are consistent with manual food processing and would have facilitated powerful grasping, such as that used in climbing. These fossils suggest that P. boisei was capable of tool making and use in some capacity while also supporting the proposed dichotomy of distinct dietary adaptations between Paranthropus and Homo. In addition to offering insights into the poorly known postcranial functional anatomy of Paranthropus, this discovery illuminates broader patterns of hominin hand evolution and tool use. Analyses of newly discovered hand and foot bones of a Paranthropus boisei specimen provide insight into possible tool use and other palaeobiology characteristics among Plio-Pleistocene hominin species.

EARLY MIOCENE VEGETATION RECONSTRUCTION USING BULK ORGANIC MATTER AND PEDOGENIC CARBONATE ISOTOPE ANALYSIS FROM MORUOROT, WEST TURKANA, KENYA

Abstracts with programs - Geological Society of America · 2025-01-01

FOSSIL WOOD-ASSOCIATED DOLOMITE RECORDS AN UNUSUAL RIFT RELATED FLUID

Abstracts with programs - Geological Society of America · 2024-01-01

EARLY MIOCENE VEGETATION RECONSTRUCTION USING BULK ORGANIC MATTER AND PEDOGENIC CARBONATE ISOTOPE ANALYSIS FROM MORUOROT, WEST TURKANA, KENYA

Abstracts with programs - Geological Society of America · 2024-01-01

PALEOSOL ANALYSIS OF A MIDDLE MIOCENE PRIMATE FOSSIL SITE IN WEST TURKANA, KENYA

Abstracts with programs - Geological Society of America · 2024-01-01

PALEOENVIRONMENTS AND PALEOCLIMATE OF EARLY MIOCENE FOSSILIFEROUS STRATA AT MORUOROT, WEST TURKANA, KENYA

Abstracts with programs - Geological Society of America · 2024-01-01

HYDROTHERMAL CARBONATES FROM TURKANA, KENYA, PRESERVE EVIDENCE OF AN UNUSUAL MIDDLE MIOCENE THERMAL FLUID PULSE

Abstracts with programs - Geological Society of America · 2023-01-01